Ketogenic low-CHO, high-fat diet: the future of elite endurance sport?

International society of sports nutrition position stand: ketogenic diets

POSITION STATEMENT

The International Society of Sports Nutrition (ISSN) provides an objective and critical review of the use of a ketogenic diet in healthy exercising adults, with a focus on exercise performance and body composition. However, this review does not address the use of exogenous ketone supplements. The following points summarize the position of the ISSN.

1. A ketogenic diet induces a state of nutritional ketosis, which is generally defined as serum ketone levels above 0.5 mM. While many factors can impact what amount of daily carbohydrate intake will result in these levels, a broad guideline is a daily dietary carbohydrate intake of less than 50 grams per day.

2. Nutritional ketosis achieved through carbohydrate restriction and a high dietary fat intake is not intrinsically harmful and should not be confused with ketoacidosis, a life-threatening condition most commonly seen in clinical populations and metabolic dysregulation.

3. A ketogenic diet has largely neutral or detrimental effects on athletic performance compared to a diet higher in carbohydrates and lower in fat, despite achieving significantly elevated levels of fat oxidation during exercise (~1.5 g/min).

4. The endurance effects of a ketogenic diet may be influenced by both training status and duration of the dietary intervention, but further research is necessary to elucidate these possibilities. All studies involving elite athletes showed a performance decrement from a ketogenic diet, all lasting six weeks or less. Of the two studies lasting more than six weeks, only one reported a statistically significant benefit of a ketogenic diet.

5. A ketogenic diet tends to have similar effects on maximal strength or strength gains from a resistance training program compared to a diet higher in carbohydrates. However, a minority of studies show superior effects of non-ketogenic comparators.

6. When compared to a diet higher in carbohydrates and lower in fat, a ketogenic diet may cause greater losses in body weight, fat mass, and fat-free mass, but may also heighten losses of lean tissue. However, this is likely due to differences in calorie and protein intake, as well as shifts in fluid balance.

7. There is insufficient evidence to determine if a ketogenic diet affects males and females differently. However, there is a strong mechanistic basis for sex differences to exist in response to a ketogenic diet.

Power output at the moderate-to-heavy intensity transition decreases in a non-linear fashion during prolonged exercise

PURPOSE

The aims of this study were to: (i) describe the time course of the decrease in power output at the moderate-to-heavy intensity transition during prolonged exercise; (ii) investigate the association between durability of the moderate-to-heavy intensity transition and exercise capacity; and (iii) explore physiological correlates of durability of the moderate-to-heavy intensity transition.

METHODS

Twelve trained cyclists (age: 40 ± 8 y, V ˙ O2peak: 52.3 ± 5.2 mL·min-1·kg-1) performed an exhaustive cycling protocol involving alternating incremental exercise tests to determine power output at the moderate-to-heavy intensity transition via the first ventilatory threshold (VT1), and 30-min bouts at 90% of the power output at the previously estimated VT1 in the rested state. The individual time course of VT1 was modelled using linear and second-order polynomial functions, and time to a 5% decrease in VT1 (Δ5%VT1) was estimated using the best-fitting model.

RESULTS

Power output at VT1 decreased according to a second-order polynomial function in 11 of 12 participants. Time-to-task failure (234 ± 66 min) was correlated with Δ5%VT1 (139 ± 78 min, rs = 0.676, p = 0.016), and these were strongly correlated with absolute and relative rates of fat oxidation at specific exercise intensities measured during the incremental test performed in the rested state.

CONCLUSIONS

These data: (i) identify a non-linear time course of decreases in the moderate-to-heavy intensity transition during prolonged exercise; (ii) support the importance of durability of the moderate-to-heavy intensity transition in prolonged exercise capacity; and (iii) suggest durability of the moderate-to-heavy intensity transition is related to fat oxidation rates.

Endurance training volume cannot entirely substitute for the lack of intensity

PURPOSE

Very low intensity endurance training (LIT) does not seem to improve maximal oxygen uptake. The purpose of the present study was to investigate if very high volume of LIT could compensate the lack of intensity and is LIT affecting differently low and high intensity performances.

METHODS

Recreationally active untrained participants (n = 35; 21 females) cycled either LIT (mean training time 6.7 ± 0.7 h / week at 63% of maximal heart rate, n = 16) or high intensity training (HIT) (1.6 ± 0.2 h /week, n = 19) for 10 weeks. Two categories of variables were measured: Low (first lactate threshold, fat oxidation at low intensity exercise, post-exercise recovery) and high (aerobic capacity, second lactate threshold, sprinting power, maximal stroke volume) intensity performance.

RESULTS

Only LIT enhanced pooled low intensity performance (LIT: p = 0.01, ES = 0.49, HIT: p = 0.20, ES = 0.20) and HIT pooled high intensity performance (LIT: p = 0.34, ES = 0.05, HIT: p = 0.007, ES = 0.48).

CONCLUSIONS

Overall, very low endurance training intensity cannot fully be compensated by high training volume in adaptations to high intensity performance, but it nevertheless improved low intensity performance. Therefore, the intensity threshold for improving low intensity performance is lower than that for improving high intensity performance. Consequently, evaluating the effectiveness of LIT on endurance performance cannot be solely determined by high intensity performance tests.

Energy Availability and Interstitial Fluid Glucose Changes in Elite Male Japanese Triathletes during Training Camp: A Case Study

This study explored the impact of varying energy availability (EA) on the 24-h interstitial fluid glucose concentration (IGC) in five elite male Japanese triathletes at a training camp. Measurements of IGC, energy and macronutrient intake, and exercise energy expenditure (EEE) through metabolic equivalents (METs) from training logs were conducted. Three subjects were evaluated over two 4-day periods, and two subjects over one 4-day period. Findings revealed significant correlations of daily mean nocturnal IGC with daily EA (r = 0.553, p = 0.001) and energy intake (EI) (r = 0.595, p < 0.001). However, no significant correlation was found between mean daily nocturnal IGC and EEE (r = -0.278, p = 0.124). Daytime IGC was ≥110 mg/dL for >50% of the time in all subjects, except on 1 day in one subject, and never fell <70 mg/dL. Therefore, daily EA may influence nocturnal IGC in elite male triathletes, although high daytime IGC levels were maintained without hypoglycemia.

Dietary Patterns, Gut Microbiota and Sports Performance in Athletes: A Narrative Review

The intestinal tract of humans harbors a dynamic and complex bacterial community known as the gut microbiota, which plays a crucial role in regulating functions such as metabolism and immunity in the human body. Numerous studies conducted in recent decades have also highlighted the significant potential of the gut microbiota in promoting human health. It is widely recognized that training and nutrition strategies are pivotal factors that allow athletes to achieve optimal performance. Consequently, there has been an increasing focus on whether training and dietary patterns influence sports performance through their impact on the gut microbiota. In this review, we aim to present the concept and primary functions of the gut microbiota, explore the relationship between exercise and the gut microbiota, and specifically examine the popular dietary patterns associated with athletes' sports performance while considering their interaction with the gut microbiota. Finally, we discuss the potential mechanisms by which dietary patterns affect sports performance from a nutritional perspective, aiming to elucidate the intricate interplay among dietary patterns, the gut microbiota, and sports performance. We have found that the precise application of specific dietary patterns (ketogenic diet, plant-based diet, high-protein diet, Mediterranean diet, and high intake of carbohydrate) can improve vascular function and reduce the risk of illness in health promotion, etc., as well as promoting recovery and controlling weight with regard to improving sports performance, etc. In conclusion, although it can be inferred that certain aspects of an athlete's ability may benefit from specific dietary patterns mediated by the gut microbiota to some extent, further high-quality clinical studies are warranted to substantiate these claims and elucidate the underlying mechanisms.

Effects of a 10-Week Exercise and Nutritional Intervention with Variable Dietary Carbohydrates and Glycaemic Indices on Substrate Metabolism, Glycogen Storage, and Endurance Performance in Men: A Randomized Controlled Trial

BACKGROUND

Daily nutrition plays an important role in supporting training adaptions and endurance performance. The objective of this 10-week study was to investigate the consequences of varying carbohydrate consumption and the glycaemic index (GI) together with an endurance training regimen on substrate oxidation, muscle energy storage and endurance performance under free-living conditions. Sixty-five moderately trained healthy men (29 ± 4 years; VO2 peak 55 ± 8 mL min-1 kg-1) were randomized to one of three different nutritional regimes (LOW-GI: 50-60% CHO with ≥ 65% of these CHO with GI < 50 per day, n = 24; HIGH-GI: 50-60% CHO with ≥ 65% CHO with GI > 70 per day, n = 20; LCHF: ≤ 50 g CHO daily, n = 21). Metabolic alterations and performance were assessed at baseline (T0) and after 10 weeks (T10) during a graded exercise treadmill test. Additionally, a 5 km time trial on a 400-m outdoor track was performed and muscle glycogen was measured by magnet resonance spectroscopy.

RESULTS

Total fat oxidation expressed as area under the curve (AUC) during the graded exercise test increased in LCHF (1.3 ± 2.4 g min-1 × km h-1, p < 0.001), remained unchanged in LOW-GI (p > 0.05) and decreased in HIGH-GI (- 1.7 ± 1.5 g min-1 × km h-1, p < 0.001). After the intervention, LOW-GI (- 0.4 ± 0.5 mmol L-1 × km h-1, p < 0.001) and LCHF (- 0.8 ± 0.7 mmol L-1 × km h-1, p < 0.001) showed significantly lower AUC of blood lactate concentrations. Peak running speed increased in LOW-GI (T0: 4.3 ± 0.4 vs. T10: 4.5 ± 0.3 m s-1, p < 0.001) and HIGH-GI (T0: 4.4 ± 0.5 vs. T10: 4.6 ± 0.4 m s-1), while no improvement was observed in LCHF. Yet, time trial performance improved significantly in all groups. Muscle glycogen content increased for participants in HIGH-GI (T0: 97.3 ± 18.5 vs. T10: 144.5 ± 39.8 mmol L wet-tissue-1, p = 0.027) and remained unchanged in the LOW-GI and the LCHF group. At the last examination, muscle glycogen concentration was significantly higher in LOW-GI compared to LCHF (p = 0.014).

CONCLUSION

Changes in fat oxidation were only present in LCHF, however, lower lactate concentrations in LOW-GI resulted in changes indicating an improved substrate metabolism. Compared to a LCHF diet, changes in peak running speed, and muscle glycogen stores were superior in LOW- and HIGH-GI diets. The low GI diet seems to have an influence on substrate metabolism without compromising performance at higher intensities, suggesting that a high-carbohydrate diet with a low GI is a viable alternative to a LCHF or a high GI diet.

TRIAL REGISTRATION

Clinical Trials, NCT05241730. https://clinicaltrials.gov/study/NCT05241730 . Registered 25 January 2021.

Physiologic Adaptation to Macronutrient Change Distorts Findings from Short Dietary Trials: Reanalysis of a Metabolic Ward Study

An influential 2-wk cross-over feeding trial without a washout period purported to show advantages of a low-fat diet (LFD) compared with a low-carbohydrate diet (LCD) for weight control. In contrast to several other macronutrient trials, the diet order effect was originally reported as not significant. In light of a new analysis by the original investigative group identifying an order effect, we aimed to examine, in a reanalysis of publicly available data (16 of 20 original participants; 7 female; mean BMI, 27.8 kg/m2), the validity of the original results and the claims that trial data oppose the carbohydrate-insulin model of obesity (CIM). We found that energy intake on the LCD was much lower when this diet was consumed first compared with second (a difference of -1164 kcal/d, P = 3.6 × 10-13); the opposite pattern was observed for the LFD (924 kcal/d, P = 2.0 × 10-16). This carry-over effect was significant (P interaction = 0.0004) whereas the net dietary effect was not (P = 0.4). Likewise, the between-arm difference (LCD - LFD) was -320 kcal/d in the first period and +1771 kcal/d in the second. Body fat decreased with consumption of the LCD first and increased with consumption of this diet second (-0.69 ± 0.33 compared with 0.57 ± 0.32 kg, P = 0.007). LCD-first participants had higher β-hydroxybutyrate levels while consuming the LCD and lower respiratory quotients while consuming LFD when compared with LFD-first participants on their respective diets. Change in insulin secretion as assessed by C-peptide in the first diet period predicted higher energy intake and less fat loss in the second period. These findings, which tend to support rather than oppose the CIM, suggest that differential (unequal) carry-over effects and short duration, with no washout period, preclude causal inferences regarding chronic macronutrient effects from this trial.

Effectiveness of high-fat and high-carbohydrate diets on body composition and maximal strength after 15 weeks of resistance training

PURPOSE

The aim of this study was to compare High Carbohydrates Low Fat (HCLF) and Low Carbohydrate High Fat (LCHF) diets in terms of changes in body composition and maximal strength.

PATIENTS/METHODS

The study involved 48 men aged 25 ​± ​2.5, divided into two groups, one of which (n ​= ​23) was following the LCHF diet and the other (n ​= ​25) the HCLF diet. Both groups performed the same resistance training protocol for 15 weeks. Maximal strength in squat, bench press and deadlift was assessed pre- and post-intervention. Measurements of selected body circumferences and tissue parameters were made using the multifunctional, multi-frequency, direct bioelectric impedance InBody 770 analyzer from InBody Co., Ltd (Cerritos, California, USA). The team with the necessary qualifications and experience in research performed all the measurements and maintained participants' oversight throughout the entire length of the study.

RESULTS

Both nutritional approaches were effective in terms of reducing body fat mass. The HCLF group achieved greater skeletal muscle hypertrophy. Significant decreases in body circumferences, especially in the abdominal area, were observed for both dietary approaches. Maximal strength significantly increased in the HCLF group and decreased in the LCHF group.

CONCLUSION

Holistic analysis of the results led to the conclusion that both dietary approaches may elicit positive adaptations in body composition. The two approaches constitute useful alternatives for both recreational exercisers and physique athletes with body composition goals.

Defining ketone supplementation: the evolving evidence for postexercise ketone supplementation to improve recovery and adaptation to exercise

Over the last decade, there has been a growing interest in the use of ketone supplements to improve athletic performance. These ketone supplements transiently elevate the concentrations of the ketone bodies acetoacetate (AcAc) and d-β-hydroxybutyrate (βHB) in the circulation. Early studies showed that ketone bodies can improve energetic efficiency in striated muscle compared with glucose oxidation and induce a glycogen-sparing effect during exercise. As such, most research has focused on the potential of ketone supplementation to improve athletic performance via ingestion of ketones immediately before or during exercise. However, subsequent studies generally observed no performance improvement, and particularly not under conditions that are relevant for most athletes. However, more and more studies are reporting beneficial effects when ketones are ingested after exercise. As such, the real potential of ketone supplementation may rather be in their ability to enhance postexercise recovery and training adaptations. For instance, recent studies observed that postexercise ketone supplementation (PEKS) blunts the development of overtraining symptoms, and improves sleep, muscle anabolic signaling, circulating erythropoietin levels, and skeletal muscle angiogenesis. In this review, we provide an overview of the current state-of-the-art about the impact of PEKS on aspects of exercise recovery and training adaptation, which is not only relevant for athletes but also in multiple clinical conditions. In addition, we highlight the underlying mechanisms by which PEKS may improve exercise recovery and training adaptation. This includes epigenetic effects, signaling via receptors, modulation of neurotransmitters, energy metabolism, and oxidative and anti-inflammatory pathways.

Limits of Ultra: Towards an Interdisciplinary Understanding of Ultra-Endurance Running Performance

Ultra-endurance running (UER) poses extreme mental and physical challenges that present many barriers to completion, let alone performance. Despite these challenges, participation in UER events continues to increase. With the relative paucity of research into UER training and racing compared with traditional endurance running distance (e.g., marathon), it follows that there are sizable improvements still to be made in UER if the limitations of the sport are sufficiently understood. The purpose of this review is to summarise our current understanding of the major limitations in UER. We begin with an evolutionary perspective that provides the critical background for understanding how our capacities, abilities and limitations have come to be. Although we show that humans display evolutionary adaptations that may bestow an advantage for covering large distances on a daily basis, these often far exceed the levels of our ancestors, which exposes relative limitations. From that framework, we explore the physiological and psychological systems required for running UER events. In each system, the factors that limit performance are highlighted and some guidance for practitioners and future research are shared. Examined systems include thermoregulation, oxygen delivery and utilisation, running economy and biomechanics, fatigue, the digestive system, nutritional and psychological strategies. We show that minimising the cost of running, damage to lower limb tissue and muscle fatigability may become crucial in UER events. Maintaining a sustainable core body temperature is critical to performance, and an even pacing strategy, strategic heat acclimation and individually calculated hydration all contribute to sustained performance. Gastrointestinal issues affect almost every UER participant and can be due to a variety of factors. We present nutritional strategies for different event lengths and types, such as personalised and evidence-based approaches for varying types of carbohydrate, protein and fat intake in fluid or solid form, and how to avoid flavour fatigue. Psychology plays a vital role in UER performance, and we highlight the need to be able to cope with complex situations, and that specific long and short-term goal setting improves performance. Fatigue in UER is multi-factorial, both physical and mental, and the perceived effort or level of fatigue have a major impact on the ability to continue at a given pace. Understanding the complex interplay of these limitations will help prepare UER competitors for the different scenarios they are likely to face. Therefore, this review takes an interdisciplinary approach to synthesising and illuminating limitations in UER performance to assist practitioners and scientists in making informed decisions in practice and applicable research.

Low Carbohydrate, High Fat Diet Alters the Oral Microbiome without Negating the Nitrite Response to Beetroot Juice Supplementation

A low carbohydrate, high fat (LCHF) diet in athletes increases fat oxidation but impairs sports performance, potentially due to impaired exercise economy. Dietary nitrate supplementation can improve exercise economy via an increase in nitric oxide production, which is initiated by the reduction of nitrate to nitrite within the oral cavity. This reaction is dependent on the presence of nitrate-reducing oral bacteria, which can potentially be altered by dietary changes, including a LCHF diet. This study explored the effect of a LCHF diet on the oral microbiome and subsequent changes to plasma nitrite concentration following nitrate supplementation. Following five days of LCHF or high carbohydrate (HCHO) control dietary intervention, highly trained male race walkers consumed 140 mL beetroot juice containing 8.4 mmol nitrate; they then provided (a) blood samples for plasma nitrate and nitrite analysis and (b) saliva samples for 16S rRNA sequencing of the oral microbiome. The LCHF diet (n = 13) reduced oral bacterial diversity and changed the relative abundance of the genera Neisseria (+10%), Fusobacteria (+3%), Prevotella (-9%), and Veillonella (-4%), with no significant changes observed following the HCHO diet (n = 11). Following beetroot juice ingestion, plasma nitrite concentrations were higher for the LCHF diet compared to the HCHO diet (p = 0.04). However, the absence of an interaction with the trial (pre-post) (p = 0.71) suggests that this difference was not due to the dietary intervention. In summary, we found an increase in plasma nitrate and nitrite concentrations in response to nitrate supplementation independent of diet. This suggests the oral microbiome is adaptive to dietary changes and can maintain a nitrate reduction capacity despite a decrease in bacterial diversity following the LCHF diet.

The effect of a short-term ketogenic diet on exercise efficiency during graded exercise in healthy adults

OBJECTIVE

We examined the effects of short-term KD on exercise efficiency and hormonal response during and after the graded exercise testing.

METHODS

Fourteen untrained healthy adults (8 males, 6 females, age 26.4 ± 3.1 [SD] years; BMI 24.8 ± 4.6 kg/m2; peak VO2max 54.0 ± 5.8 ml/kg FFM/min) completed 3-days of a mixed diet (MD) followed by another 3-days of KD after 3-days of washout period. Upon completion of each diet arm, participants underwent graded exercise testing with low- (LIE; 40% of VO2max), moderate- (MIE; 55%), and high-intensity exercise (HIE; 70%). Exercise efficiency was calculated as work done (kcal/min)/energy expenditure (kcal/min).

RESULTS

Fat oxidation during the recovery period was higher in KD vs. MD. Despite identical workload during HIE, participants after having KD vs. MD showed higher energy expenditure and lower exercise efficiency (10.1 ± 0.7 vs. 12.5 ± 0.3%, p < .01). After KD, free fatty acid (FFA) concentrations were higher during MIE and recovery vs. resting, and beta-hydroxybutylate (BOHB) was lower at HIE vs. resting. Cortisol concentrations after KD was higher during recovery vs. resting, with no significant changes during graded exercise testing after MD.

CONCLUSIONS

Our data suggest that short-term KD is favorable to fat metabolism leading increased circulating FFA and BOHB during LIE to MIE. However, it is notable that KD may cause 1) exercise inefficiency manifested by increased energy expenditure and 2) elevated exercise stress during HIE and recovery. Trial registration: KCT0005172, International Clinical Trials Registry Platform.

Recovery Phase Nutrition and Insulin Strategies for a Collegiate Distance Runner with Type 1 Diabetes Mellitus: A Case Study

PURPOSE

There is scant published research regarding nutrition and insulin strategies for athletic performance in collegiate distance runners with type 1 diabetes mellitus (CDRT1). Acute carbohydrate supplementation (CHOsup) and insulin reduction used to minimize hypoglycemia during exercise may result in deteriorated glycemic control post exercise in CDRT1. The present case study of a CDRT1 investigated outcomes associated with a moderate-carbohydrate (ModCHO) diet and 24 h insulin adjustment during recovery phases for improved glycemic control and reduced use of acute strategies.

METHODS

During an 8-day period, a female CDRT1 followed a ModCHO (~4 g/kg/day) nutrition program. Recovery phase adjustments to insulin doses were made using an equation developed to estimate reduced insulin needs post exercise, as a function of exercise intensity and duration. Daily training was performed in the fasted state at 6:00 a.m. and included additional exercise strategies to reduce glycemic variability when needed. Daily blood glucose time-in-range (TIR) and use of CHOsup were assessed. Athlete well-being was determined using the Student-Athlete Well-Being Scale (SAWS)TM at baseline, and days 1, 3, and 7.

RESULTS

Throughout the 8-day period, mean TIR increased (77% versus < 50%) and the magnitude of glycemic excursions decreased (~3.8-15 versus ~3.0-26 mmol/L) relative to a prior comparison period. Minimal pre-exercise CHOsup was employed and CHOsup during exercise was not required. Additionally, the athlete achieved a new lifetime best in the 5000 m run and maintained positive well-being.

CONCLUSION

The present case study provides examples of recovery phase strategies (i.e., ModCHO diet and 24 h insulin adjustments) that may support glycemic control and athletic performance in CDRT1 and provides potential considerations for nutrition and insulin strategies for use by athletes and coaches.

Iron Status and Physical Performance in Athletes

Iron is an important mineral in the body, essential for muscle function and oxygen transport. Adequate levels of iron in the blood are necessary for athletes, as iron-deficiency anemia can reduce physical performance. Several studies have investigated iron status and supplementation in iron-deficient athletes, and determined how physical strain can change iron balance and markers related to iron status. The question of how to influence and optimize iron status, as well as other markers that can affect iron metabolism, has been less thoroughly investigated. Therefore, the aim of this review is to take a closer look at the importance of iron values, iron markers, and factors that can change iron metabolism for physical performance and the extent to which physical performance can be influenced in a positive or negative way. A systematic search of the PubMed database was performed, with the use of « iron» or «iron deficiency» or «hemoglobin» AND «athletes» AND «athletic performance» as a strategy of the search. After the search, 11 articles were included in the review after the application of inclusion and exclusion criteria. Major findings include that iron supplementation had the best effect in athletes with the lowest iron status, and effects on physical performance were mostly achieved in those who were originally in a deficit. Iron supplementation could be beneficial for optimal erythropoietic response during altitude training, even in athletes with normal iron stores at baseline, but should be performed with caution. Alteration of the hepcidin response can affect the use of existing iron stores for erythropoiesis. Energy intake, and the amount of carbohydrates available, may have an impact on the post-exercise hepcidin response. Optimal vitamin D and B12 levels can possibly contribute to improved iron status and, hence, the avoidance of anemia.

High-fat ketogenic diets and ketone monoester supplements differentially affect substrate metabolism during aerobic exercise

Chronically adhering to high-fat ketogenic diets or consuming ketone monoester supplements elicits ketosis. Resulting changes in substrate metabolism appear to be drastically different between ketogenic diets and ketone supplements. Consuming a ketogenic diet increases fatty acid oxidation with concomitant decreases in endogenous carbohydrate oxidation. Increased fat oxidation eventually results in an accumulation of circulating ketone bodies, which are metabolites of fatty acids that serve as an alternative source of fuel. Conversely, consuming ketone monoester supplements rapidly increases circulating ketone body concentrations that typically exceed those achieved by adhering to ketogenic diets. Rapid increases in ketone body concentrations with ketone monoester supplementation elicit a negative feedback inhibition that reduces fatty acid mobilization during aerobic exercise. Supplement-derived ketosis appears to have minimal impact on sparing of muscle glycogen or minimizing of carbohydrate oxidation during aerobic exercise. This review will discuss the substrate metabolic and associated aerobic performance responses to ketogenic diets and ketone supplements.

Popular Dietary Trends' Impact on Athletic Performance: A Critical Analysis Review

BACKGROUND

Nutrition fuels optimal performance for athletes. With increased research developments, numerous diets available, and publicity from professional athletes, a review of dietary patterns impact on athletic performance is warranted.

RESULTS

The Mediterranean diet is a low inflammatory diet linked to improved power and muscle endurance and body composition. Ketogenic diets are restrictive of carbohydrates and proteins. Though both show no decrements in weight loss, ketogenic diets, which is a more restrictive form of low-carbohydrate diets, can be more difficult to follow. High-protein and protein-paced versions of low-carbohydrate diets have also shown to benefit athletic performance. Plant-based diets have many variations. Vegans are at risk of micronutrient deficiencies and decreased leucine content, and therefore, decreased muscle protein synthesis. However, the literature has not shown decreases in performance compared to omnivores. Intermittent fasting has many different versions, which may not suit those with comorbidities or specific needs as well as lead to decreases in sprint speed and worsening time to exhaustion.

CONCLUSIONS

This paper critically evaluates the research on diets in relation to athletic performance and details some of the potential risks that should be monitored. No one diet is universally recommend for athletes; however, this article provides the information for athletes to analyze, in conjunction with medical professional counsel, their own diet and consider sustainable changes that can help achieve performance and body habitus goals.

Longer-Term Effects of the Glycaemic Index on Substrate Metabolism and Performance in Endurance Athletes

Nutrition has a decisive influence on athletic performance. However, it is not only the nutrient intake during exercise that is important, but the daily diet must also be adapted to the requirements of physical activity in order to optimally promote training adaptations. The goal of prolonged endurance training is to enhance fat oxidation, to maintain aerobic performance at a higher intensity while sparing limited carbohydrate stores. The targeted modification of macronutrient intake is a common method of influencing substrate metabolism, fuel selection, and performance. However, it is not well established whether the glycaemic index of carbohydrates in our daily diet can improve endurance performance by influencing carbohydrate or fat oxidation during training. Therefore, the aim of the following review is to elucidate the possible influence of the glycaemic index on substrate utilization during exercise and to clarify whether the consumption of a long-term high-carbohydrate diet with different glycaemic indices may have an influence on substrate metabolism and endurance performance.

Ketogenic diets, exercise performance, and training adaptations

PURPOSE OF REVIEW

The ketogenic diet has been proposed as a nutritional strategy in sports. This review was undertaken to provide an overview of the recent literature concerning the effects of ketogenic diet on exercise performance and training adaptations.

RECENT FINDINGS

Most recent literature on the ketogenic diet and exercise performance showed no beneficial effects, especially for trained individuals. During a period of intensified training, performance was clearly impaired during the ketogenic intervention, while a diet with high carbohydrates maintained physical performance. The main effect of the ketogenic diet resides in metabolic flexibility, inducing the metabolism to oxidize more fat for ATP resynthesis regardless of submaximal exercise intensities.

SUMMARY

The ketogenic diet is not a reasonable nutritional strategy, as it has no advantage over normal/high carbohydrate-based diets on physical performance and training adaptations even when used only in a specific training/nutritional periodization stage.

Adherence to a Ketogenic Low-Carbohydrate, High-Fat Diet Is Associated With Diminished Training Quality in Elite Racewalkers

PURPOSE

To examine the effects of a high-carbohydrate diet (HCHO), periodized-carbohydrate (CHO) diet (PCHO), and ketogenic low-CHO high-fat diet (LCHF) on training capacity.

METHODS

Elite male racewalkers completed 3 weeks of periodic training while adhering to their dietary intervention. Twenty-nine data sets were collected from 21 athletes. Each week, 6 mandatory training sessions were completed, with additional sessions performed at the athlete's discretion. Mandatory sessions included an interval session (10 × 1-km efforts on a 6-min cycle), tempo session (14 km with a 450-m elevation gain), 2 long walks (25-40 km), and 2 easy walks (8-12 km) where "sleep-low" and "train-low" dietary strategies were employed for PCHO. Racewalking speed, heart rate, rating of perceived exhaustion, and blood metabolites were collected around key sessions.

RESULTS

LCHF covered less total distance than HCHO and PCHO (P < .001); however, no differences in training load between groups were evident (P = .285). During the interval sessions, walking speed was slower in LCHF (P = .001), equating to a 2.8% and 5.6% faster speed in HCHO and PCHO, respectively. LCHF was also 3.2% slower in completing the tempo session than HCHO and PCHO (P = .001). Heart rate was higher (P = .002) and lactate concentrations were lower (P < .001) in LCHF compared to other groups, despite slower walking speeds during the interval session. No between-groups differences in rating of perceived exhaustion were evident (P = .077).

CONCLUSION

Athletes adhering to an LCHF diet showed impaired training capacity relative to their high-CHO-supported counterparts, completing lower training volumes at slower speeds, with higher heart rates.

Different Effects of Cyclical Ketogenic vs. Nutritionally Balanced Reduction Diet on Serum Concentrations of Myokines in Healthy Young Males Undergoing Combined Resistance/Aerobic Training

Myokines represent important regulators of muscle metabolism. Our study aimed to explore the effects of a cyclical ketogenic reduction diet (CKD) vs. a nutritionally balanced reduction diet (RD) combined with regular resistance/aerobic training in healthy young males on serum concentrations of myokines and their potential role in changes in physical fitness. Twenty-five subjects undergoing regular resistance/aerobic training were randomized to the CKD (n = 13) or RD (n = 12) groups. Anthropometric and spiroergometric parameters, muscle strength, biochemical parameters, and serum concentrations of myokines and cytokines were assessed at baseline and after 8 weeks of intervention. Both diets reduced body weight, body fat, and BMI. Muscle strength and endurance performance were improved only by RD. Increased musclin (32.9 pg/mL vs. 74.5 pg/mL, p = 0.028) and decreased osteonectin levels (562 pg/mL vs. 511 pg/mL, p = 0.023) were observed in RD but not in the CKD group. In contrast, decreased levels of FGF21 (181 pg/mL vs. 86.4 pg/mL, p = 0.003) were found in the CKD group only. Other tested myokines and cytokines were not significantly affected by the intervention. Our data suggest that changes in systemic osteonectin and musclin levels could contribute to improved muscle strength and endurance performance and partially explain the differential effects of CKD and RD on physical fitness.

Low carbohydrate high fat ketogenic diets on the exercise crossover point and glucose homeostasis

In exercise science, the crossover effect denotes that fat oxidation is the primary fuel at rest and during low-intensity exercise with a shift towards an increased reliance on carbohydrate oxidation at moderate to high exercise intensities. This model makes four predictions: First, &gt;50% of energy comes from carbohydrate oxidation at ≥60% of maximum oxygen consumption (VO2max), termed the crossover point. Second, each individual has a maximum fat oxidation capacity (FATMAX) at an exercise intensity lower than the crossover point. FATMAX values are typically 0.3–0.6 g/min. Third, fat oxidation is minimized during exercise ≥85%VO2max, making carbohydrates the predominant energetic substrate during high-intensity exercise, especially at &gt;85%VO2max. Fourth, high-carbohydrate low-fat (HCLF) diets will produce superior exercise performances via maximizing pre-exercise storage of this predominant exercise substrate. In a series of recent publications evaluating the metabolic and performance effects of low-carbohydrate high-fat (LCHF/ketogenic) diet adaptations during exercise of different intensities, we provide findings that challenge this model and these four predictions. First, we show that adaptation to the LCHF diet shifts the crossover point to a higher %VO2max (&gt;80%VO2max) than previously reported. Second, substantially higher FATMAX values (&gt;1.5 g/min) can be measured in athletes adapted to the LCHF diet. Third, endurance athletes exercising at &gt;85%VO2max, whilst performing 6 × 800 m running intervals, measured the highest rates of fat oxidation yet reported in humans. Peak fat oxidation rates measured at 86.4 ± 6.2%VO2max were 1.58 ± 0.33 g/min with 30% of subjects achieving &gt;1.85 g/min. These studies challenge the prevailing doctrine that carbohydrates are the predominant oxidized fuel during high-intensity exercise. We recently found that 30% of middle-aged competitive athletes presented with pre-diabetic glycemic values while on an HCLF diet, which was reversed on LCHF. We speculate that these rapid changes between diet, insulin, glucose homeostasis, and fat oxidation might be linked by diet-induced changes in mitochondrial function and insulin action. Together, we demonstrate evidence that challenges the current crossover concept and demonstrate evidence that a LCHF diet may also reverse features of pre-diabetes and future metabolic disease risk, demonstrating the impact of dietary choice has extended beyond physical performance even in athletic populations.

Effect of ketogenic diet on exercise tolerance and transcriptome of gastrocnemius in mice

Ketogenic diet (KD) has been proven to be an optional avenue in weight control. However, the impacts of KD on muscle strength and exercise endurance remain unclear. In this study, mice were randomly allocated to normal diet and KD groups to assess their exercise tolerance and transcriptomic changes of the gastrocnemius. KD suppressed body-weight and glucose levels and augmented blood ketone levels of mice. The total cholesterol, free fatty acids, and β-hydroxybutyric acid levels were higher and triglycerides and aspartate aminotransferase levels were lower in KD group. There was no notable difference in running distance/time and weight-bearing swimming time between the two groups. Furthermore, KD alleviated the protein levels of PGC-1α, p62, TnI FS, p-AMPKα, and p-Smad3, while advancing the LC3 II and TnI SS protein levels in the gastrocnemius tissues. RNA-sequencing found that 387 differentially expressed genes were filtered, and Cpt1b, Acadl, Eci2, Mlycd, Pdk4, Ptprc, C1qa, Emr1, Fcgr3, and Ctss were considered to be the hub genes. Our findings suggest that KD effectively reduced body weight but did not affect skeletal muscle strength and exercise endurance via AMPK/PGC-1α, Smad3, and p62/LC3 signaling pathways and these hub genes could be potential targets for muscle function in KD-treated mice.

Effect of a low carbohydrate, high fat diet versus a high carbohydrate diet on exercise efficiency and economy in recreational male athletes

BACKGROUND

Exercise efficiency and economy are key determinants of endurance exercise performance. In this cross-over intervention trial, we investigated the effect of adherence to a low carbohydrate, high fat (LCHF) diet versus a high carbohydrate (HC) diet on gross efficiency (GE) and (OC) during exercise, both after 2 days and after 14 days of adherence.

METHODS

Fourteen recreational male athletes followed a two-week LCHF diet (<10 energy % carbohydrate) and a two-week HC diet (>50 energy % carbohydrate), in random order, with a wash-out period of three weeks in between. After 2 and 14 days on each diet, the athletes performed a 90-minutes submaximal exercise session on a bicycle ergometer. Indirect calorimetry measurements were done after 60 minutes of exercise to calculate GE and OC.

RESULTS

GE was significantly lower on the LCHF diet compared to the HC diet, after 2 days (17.6±1.9 vs. 18.8±1.2%, P=0.011, for the LCHF and HC diet respectively), not after 14 days. OC was significantly higher on the LCHF diet compared to the HC diet, after 2 days (1191±138 vs. 1087±72 mL O<inf>2</inf>/kCal, P=0.003, for the LCHF and HC diet respectively), and showed a strong tendency to remain higher after 14 days, P=0.018.

CONCLUSIONS

Although LCHF diets are popular strategies to increase fat oxidation during exercise, adherence to a LCHF diet was associated with a lower exercise efficiency and economy compared to a HC diet.

The Effects of Concurrent Training Combined with Low-Carbohydrate High-Fat Ketogenic Diet on Body Composition and Aerobic Performance: A Systematic Review and Meta-Analysis

(1) Background: Recently, studies have emerged to explore the effects of concurrent training (CT) with a low-carb, high-fat ketogenic diet (LCHF) on body composition and aerobic performance and observed its benefits. However, a large variance in the study design and observations is presented, which needs to be comprehensively assessed. We here thus completed a systematic review and meta-analysis to characterize the effects of the intervention combining CT and LCHF on body composition and aerobic capacity in people with training experience as compared to that combining CT and other dietary strategies. (2) Methods: A search strategy based on the PICOS principle was used to find literature in the databases of PubMed, Web of Science, EBSCO, Sport-discuss, and Medline. The quality and risk of bias in the studies were independently assessed by two researchers. (3) Result: Eight studies consisting of 170 participants were included in this work. The pooled results showed no significant effects of CT with LCHF on lean mass (SMD = -0.08, 95% CI -0.44 to 0.3, p = 0.69), body fat percentage (SMD = -0.29, 95% CI -0.66 to 0.08, p = 0.13), body mass (SMD = -0.21, 95% CI -0.53 to 0.11, p = 0.2), VO_2max (SMD = -0.01, 95% CI -0.4 to 0.37, p = 0.95), and time (or distance) to complete the aerobic tests (SMD = -0.02, 95% CI -0.41 to 0.37, p = 0.1). Subgroup analyses also showed that the training background of participants (i.e., recreationally trained participants or professionally trained participants) and intervention duration (e.g., > or ≤six weeks) did not significantly affect the results. (4) Conclusions: This systematic review and meta-analysis provide evidence that compared to other dietary strategies, using LCHF with CT cannot induce greater benefits for lean mass, body fat percentage, body mass, VO_2max, and aerobic performance in trained participants.

Analysis of the Nutritional Value of the Diets Presented in Women's and Sports Magazines before and during the COVID-19 Pandemic

For consumers, among the most important sources of information related to nutrition are popular journals and magazines, including women’s and sports, but the diets presented there may lead to unhealthy weight-control behaviors. The aim of the study was to assess the nutritional value of regular and low-calorie diets presented in Polish women’s and sports magazines before and during COVID-19 pandemic. The study was based on two popular Polish magazines—one women’s magazine and one sports magazine, which regularly present various types of diets. The nutritional value of all the diets published from January 2014 to May 2022 was analyzed. The total number of included single-day menus was n = 119, while for analysis they were stratified based on: type of magazine (published in the women’s magazine n = 41 and in the sports magazine n = 78), year of publication (before the COVID-19 pandemic n = 78 and during n = 41), and type of diet (regular n = 61 and low-calorie n = 58). The analysis included the energy value and nutritional value. For the type of magazine, the diets published in the sports magazine were characterized by a higher intake of fat (p < 0.0001 for intake in grams and in % of energy) and calcium (p = 0.0330), whereas the diets published in the women’s magazine were characterized by a higher intake of carbohydrates (p = 0.0226 for intake in grams, and p = 0.0002 for intake in % of energy) and fiber (p = 0.0163). For the year of publication, the diets published during the COVID-19 pandemic were characterized by a higher intake of protein (p = 0.0166 for intake in grams), sodium (p = 0.0465), calcium (p < 0.0001), vitamin D (p = 0.0197), vitamin B6 (p = 0.0207), and vitamin B12 (p = 0.0277), whereas the diets published before the COVID-19 pandemic were characterized by a higher intake of carbohydrates (p = 0.0243 for intake in % of energy). For the type of diet, the regular diets were characterized by a higher energy value (p = 0.0020), as well as by a higher intake of fat (p = 0.0162 for intake in grams), carbohydrates (p = 0.0390 for intake in grams), mono- and oligosaccharides (p = 0.0084 for intake in % of energy), fiber (p < 0.0001), magnesium (p = 0.0323), iron (p = 0.0307), and vitamin B6 (p = 0.0204). The nutritional value of the diets presented in the Polish women’s and sports magazines was not justified by the type of magazine or type of diet, associated with the target group, which may cause the following of improperly balanced diets. However, the changes in the typical nutritional value of diets presented in the Polish women’s and sports magazines during the COVID-19 pandemic were justified by some specific needs for the prevention and treatment of COVID-19.

Octanoic Acid-Enrichment Diet Improves Endurance Capacity and Reprograms Mitochondrial Biogenesis in Skeletal Muscle of Mice

Background: Medium Chain Fatty Acids (MCFAs) are a dietary supplement that exhibit interesting properties, due to their smaller molecular size. The acute consumption of MCFAs is expected to enhance exercise performance. However, the short-term effects of MCFAs on endurance performance remains poorly understood. The aim of our study is to evaluate the octanoic acid (C8)-rich diet effect on endurance capacity, and to explore their molecular and cellular effects. Methods: C57BL/6J mice were fed with a chow diet (Control group) or an octanoic acid-rich diet (C8 diet) for 6 weeks. Spontaneous activity, submaximal and maximal exercise tests were carried out to characterize the exercise capacities of the mice. Beta-oxidation and mitochondrial biogenesis pathways were explored in skeletal muscle by RT-qPCR, Western Blot (Quadriceps) and histochemical staining (Gastrocnemius). Results: Mice fed with a C8-rich diet presented a higher spontaneous activity (p < 0.05) and endurance capacities (p < 0.05) than the control, but no effect on maximal effort was observed. They also presented changes in the skeletal muscle metabolic phenotype, with a higher number of the oxidative fibers, rich in mitochondria. At the molecular level, the C8-diet induced an AMPK activation (p < 0.05), associated with a significant increase in PGC1a and CS gene expression and protein levels. Conclusion: Our study provided evidence that C8-enrichment as a food supplementation improves endurance capacities and activates mitochondrial biogenesis pathways leading to higher skeletal muscle oxidative capacities.

Ketogenic diets, physical activity and body composition: a review

Obesity remains a serious relevant public health concern throughout the world despite related countermeasures being well understood (i.e. mainly physical activity and an adjusted diet). Among different nutritional approaches, there is a growing interest in ketogenic diets (KD) to manipulate body mass (BM) and to enhance fat mass loss. KD reduce the daily amount of carbohydrate intake drastically. This results in increased fatty acid utilisation, leading to an increase in blood ketone bodies (acetoacetate, 3-β-hydroxybutyrate and acetone) and therefore metabolic ketosis. For many years, nutritional intervention studies have focused on reducing dietary fat with little or conflicting positive results over the long term. Moreover, current nutritional guidelines for athletes propose carbohydrate-based diets to augment muscular adaptations. This review discusses the physiological basis of KD and their effects on BM reduction and body composition improvements in sedentary individuals combined with different types of exercise (resistance training or endurance training) in individuals with obesity and athletes. Ultimately, we discuss the strengths and the weaknesses of these nutritional interventions together with precautionary measures that should be observed in both individuals with obesity and athletic populations. A literature search from 1921 to April 2021 using Medline, Google Scholar, PubMed, Web of Science, Scopus and Sportdiscus Databases was used to identify relevant studies. In summary, based on the current evidence, KD are an efficient method to reduce BM and body fat in both individuals with obesity and athletes. However, these positive impacts are mainly because of the appetite suppressive effects of KD, which can decrease daily energy intake. Therefore, KD do not have any superior benefits to non-KD in BM and body fat loss in individuals with obesity and athletic populations in an isoenergetic situation. In sedentary individuals with obesity, it seems that fat-free mass (FFM) changes appear to be as great, if not greater, than decreases following a low-fat diet. In terms of lean mass, it seems that following a KD can cause FFM loss in resistance-trained individuals. In contrast, the FFM-preserving effects of KD are more efficient in endurance-trained compared with resistance-trained individuals.

Effects of the ketogenic diet on performance and body composition in athletes and trained adults: a systematic review and Bayesian multivariate multilevel meta-analysis and meta-regression

This systematic review with meta-analysis aimed to determine the effects of the ketogenic diet (KD) against carbohydrate (CHO)-rich diets on physical performance and body composition in trained individuals. The MEDLINE, EMBASE, CINAHL, SPORTDiscus, and The Cochrane Library were searched. Randomized and non-randomized controlled trials in athletes/trained adults were included. Meta-analytic models were carried out using Bayesian multilevel models. Eighteen studies were included providing estimates on cyclic exercise modes and strength one-maximum repetition (1-RM) performances and for total, fat, and free-fat masses. There were more favorable effects for CHO-rich than KD on time-trial performance (mode [95% credible interval]; -3.3% [-8.5%, 1.7%]), 1-RM (-5.7% [-14.9%, 2.6%]), and free-fat mass (-0.8 [-3.4, 1.9] kg); effects were more favorable to KD on total (-2.4 [-6.2, 1.8] kg) and fat mass losses (-2.4 [-5.4, 0.2] kg). Likely modifying effects on cyclic performance were the subject's sex and VO2max, intervention and performance durations, and mode of exercise. The intervention duration and subjects' sex were likely to modify effects on total body mass. KD can be a useful strategy for total and fat body losses, but a small negative effect on free-fat mass was observed. KD was not suitable for enhancing strength 1-RM or high-intensity cyclic performances.

Cognitive, Sleep, and Autonomic Responses to Induction of a Ketogenic Diet in Military Personnel: A Pilot Study

BACKGROUND: This pilot study examined the effect of a 2-wk ketogenic diet (KD) compared with a carbohydrate (CHO) diet in military personnel on cognitive performance, mood, sleep, and heart rate variability (HRV).METHODS: A randomized-controlled, cross-over trial was conducted with eight male military personnel (age, 36 ± 7 yr; body mass, 83.7 ± 9.2 kg; BMI, 26.0 ± 2.3 kg · m−2). Subjects ingested their habitual diet for 7 d (baseline), then an iso-energetic KD (∼25 g CHO/d) or CHO diet (∼285 g CHO/d) for 14 d (adaptation), separated by a 12-d washout. HRV, fasting capillary blood D-βHB, and glucose concentration, mood, and sleep were measured daily. Cognitive performance was measured on the 7th day of baseline and the 7th and 14th days of adaptation. Data were analyzed using a series of linear mixed models.RESULTS: Mean weekly D-βHB was higher (95% CI, +0.34 to +2.38 mmol · L−1) and glucose was lower (−0.45 to −0.21 mmol · L−1) in the KD compared with the CHO diet. Cognitive performance (Psychomotor Vigilance Task, 2-choice reaction time, and running memory continuous performance test) and mean weekly fatigue, vigor, and sleep (sleep duration, sleep efficiency, and sleep onset latency) were similar between diets. A diet × week interaction for HRV approached significance, with exploratory analyses suggesting HRV was lower compared with baseline during week-2 adapt (−27 to +4 ms) in the KD.DISCUSSION: A 2-wk induction to a KD in male military personnel does not appear to affect cognitive performance, mood, or sleep, but may lower HRV, indicating increased physiological stress.Shaw DM, Henderson L, van den Berg M. Cognitive, sleep, and autonomic responses to induction of a ketogenic diet in military personnel: a pilot study. Aerosp Med Hum Perform. 2022; 93(6):507–516.

Short-Term Very High Carbohydrate Diet and Gut-Training Have Minor Effects on Gastrointestinal Status and Performance in Highly Trained Endurance Athletes

We implemented a multi-pronged strategy (MAX) involving chronic (2 weeks high carbohydrate [CHO] diet + gut-training) and acute (CHO loading + 90 g·h−1 CHO during exercise) strategies to promote endogenous and exogenous CHO availability, compared with strategies reflecting lower ranges of current guidelines (CON) in two groups of athletes. Nineteen elite male race walkers (MAX: 9; CON:10) undertook a 26 km race-walking session before and after the respective interventions to investigate gastrointestinal function (absorption capacity), integrity (epithelial injury), and symptoms (GIS). We observed considerable individual variability in responses, resulting in a statistically significant (p < 0.001) yet likely clinically insignificant increase (Δ 736 pg·mL−1) in I-FABP after exercise across all trials, with no significant differences in breath H2 across exercise (p = 0.970). MAX was associated with increased GIS in the second half of the exercise, especially in upper GIS (p < 0.01). Eighteen highly trained male and female distance runners (MAX: 10; CON: 8) then completed a 35 km run (28 km steady-state + 7 km time-trial) supported by either a slightly modified MAX or CON strategy. Inter-individual variability was observed, without major differences in epithelial cell intestinal fatty acid binding protein (I-FABP) or GIS, due to exercise, trial, or group, despite the 3-fold increase in exercise CHO intake in MAX post-intervention. The tight-junction (claudin-3) response decreased in both groups from pre- to post-intervention. Groups achieved a similar performance improvement from pre- to post-intervention (CON = 39 s [95 CI 15−63 s]; MAX = 36 s [13−59 s]; p = 0.002). Although this suggests that further increases in CHO availability above current guidelines do not confer additional advantages, limitations in our study execution (e.g., confounding loss of BM in several individuals despite a live-in training camp environment and significant increases in aerobic capacity due to intensified training) may have masked small differences. Therefore, athletes should meet the minimum CHO guidelines for training and competition goals, noting that, with practice, increased CHO intake can be tolerated, and may contribute to performance outcomes.

The effects of endogenously- and exogenously-induced hyperketonemia on exercise performance and adaptation

Elevating blood ketones may enhance exercise capacity and modulate adaptations to exercise training; however, these effects may depend on whether hyperketonemia is induced endogenously through dietary carbohydrate restriction, or exogenously through ketone supplementation. To determine this, we compared the effects of endogenously- and exogenously-induced hyperketonemia on exercise capacity and adaptation. Trained endurance athletes undertook 6 days of laboratory based cycling ("race") whilst following either: a carbohydrate-rich control diet (n = 7; CHO); a carbohydrate-rich diet + ketone drink four-times daily (n = 7; Ex Ket); or a ketogenic diet (n = 7; End Ket). Exercise capacity was measured daily, and adaptations in exercise metabolism, exercise physiology and postprandial insulin sensitivity (via an oral glucose tolerance test) were measured before and after dietary interventions. Urinary β-hydroxybutyrate increased by ⁓150-fold and ⁓650-fold versus CHO with Ex Ket and End Ket, respectively. Exercise capacity was increased versus pre-intervention by ~5% on race day 1 with CHO (p < 0.05), by 6%-8% on days 1, 4, and 6 (all p < 0.05) with Ex Ket and decreased by 48%-57% on all race days (all p > 0.05) with End Ket. There was an ⁓3-fold increase in fat oxidation from pre- to post-intervention (p < 0.05) with End Ket and increased perceived exercise exertion (p < 0.05). No changes in exercise substrate metabolism occurred with Ex Ket, but participants had blunted postprandial insulin sensitivity (p < 0.05). Dietary carbohydrate restriction and ketone supplementation both induce hyperketonemia; however, these are distinct physiological conditions with contrasting effects on exercise capacity and adaptation to exercise training.

Photosensitized oxidation of cholesterol and altered oxysterol levels in sour cream: Effects of addition of cucumber pickles

The aim of this research was to examine whether sour cream (18% fat) is an exogenous source of oxysterols and whether it is possible to improve its antioxidative properties and to modulate cholesterol transformation by adding cucumber. To determine whether cucumber modifies the properties of sour cream, fresh cucumber or cucumber pickle (pH 3.3; 1.5% lactic acid) was added in an amount of 20%. The sour cream samples were then stored under light (450 lx, 590 cd, 120 lm) for 3 wk. After storage, the addition of the cucumber pickle increased total mesophilic aerobic bacteria from 7.5 to 9.3 log cfu/g and increased the l-lactic acid content from 6.1 to 9.7 g/L. The total conjugated linoleic acid content in sour cream with cucumber pickle also increased to 4.5 mg/g fat after storage, whereas the cholesterol content decreased to 3.44 g/kg fat. Importantly, with the addition of cucumber pickle, the total content of cholesterol oxidization products (COP) did not change after storage (1.7 mg/kg fat). By contrast, the total COP content in the control sour cream sample increased from 1.7 to 7.3 mg/kg fat over 3 wk of storage. The dominant COP before and after storage was 7β-hydroxycholesterol. Thus, despite exposure to light, adding cucumber pickle to sour cream modulates cholesterol transformation and effectively inhibits the formation of oxysterols.

Efficacy of Nutritional Strategies on the Improvement of the Performance and Health of the Athlete: A Systematic Review

Evidence shows that the use of food strategies can impact health, but a clear consensus about how the effects of different food strategies impact improvement in the athlete’s performance and health remain unclear. This study evaluated how food strategies, specifically intermittent fasting and a ketogenic diet affect health and performance in healthy athletes. Study selection for this review was based on clinical trial studies analyzing changes in performance and health in athletes. The Pubmed, Web of Science, PEDro, Dialnet, Scopus, CINAHL, ProQuest, Medline and Cochrane databases were searched. The Physiotherapy Evidence Database (PEDro) scale, PEDro Internal Validity Scale (IVS) and Standard Quality Assessment Criteria for Evaluating Primary Research Papers from a variety of fields (QUALSYT) checklists were used to evaluate the risk of bias of the included studies. Articles were selected based on criteria concerning the effectiveness of nutritional strategies on athletes’ performance; articles should be randomized clinical trials (RCTs) or uncontrolled clinical trials; they should be human studies and they should have been published less than 7 years ago. A total of 15 articles were evaluated, 8 randomised clinical trials and 7 non-randomized clinical studies, with 411 participants who satisfied our inclusion criteria and were included in this review. The results of the study showed intermittent fasting and time-restricted feeding as strategies that produce health benefits. On the other hand, the ketogenic diet did not reach an appropriate consensus. The articles presented a medium level of methodological quality in the PEDro scale, low quality in IVS scale and high quality in QUALSYT scale. Despite the lack of studies analyzing changes in the performance and health of athletes after the use of different nutritional strategies, intermittent fasting and time-restricted feeding should be considered since they seem to be effective, and further studies are necessary.

High intramuscular triglyceride turnover rates and the link to insulin sensitivity: influence of obesity, type 2 diabetes and physical activity

Large intramuscular triglyceride (IMTG) stores in sedentary, obese individuals have been linked to insulin resistance, yet well-trained athletes exhibit high IMTG levels whilst maintaining insulin sensitivity. Contrary to previous assumptions, it is now known that IMTG content per se does not result in insulin resistance. Rather, insulin resistance is caused, at least in part, by the presence of high concentrations of harmful lipid metabolites, such as diacylglycerols and ceramides in muscle. Several mechanistic differences between obese sedentary individuals and their highly trained counterparts have been identified, which determine the differential capacity for IMTG synthesis and breakdown in these populations. In this review, we first describe the most up-to-date mechanisms by which a low IMTG turnover rate (both breakdown and synthesis) leads to the accumulation of lipid metabolites and results in skeletal muscle insulin resistance. We then explore current and potential exercise and nutritional strategies that target IMTG turnover in sedentary obese individuals, to improve insulin sensitivity. Overall, improving IMTG turnover should be an important component of successful interventions that aim to prevent the development of insulin resistance in the ever-expanding sedentary, overweight and obese populations. Novelty: A description of the most up-to-date mechanisms regulating turnover of the IMTG pool. An exploration of current and potential exercise/nutritional strategies to target and enhance IMTG turnover in obese individuals. Overall, highlights the importance of improving IMTG turnover to prevent the development of insulin resistance.

Low-carbohydrate, high-fat diet and running exercise influence bone parameters in old mice

We examined the effects and interactions of a low-carbohydrate, high-fat (LCHF) diet and voluntary running exercise on bone in older mice. Male 19-month-old mice were divided into four groups by diet (control vs. LCHF) and exercise (sedentary vs. voluntary running). The control diet was 55% carbohydrate, 23% protein, and 22% fat, and the LCHF diet was 10% carbohydrate, 33% protein, and 57% fat as percentages of calories. The experiment ended when the mice reached 24 months old. Statistical analysis was conducted using two-way analysis of variance with diet and exercise. The LCHF diet decreased bone mineral content (BMC), bone mineral density, bone volume fraction, and trabecular number. There was no significant interaction between diet and exercise on many bone parameters. However, there were significant diet and exercise interactions on lumbar BMC and tibial trabecular total tissue volume and average cortical thickness. The LCHF diet attenuated the benefit of running exercise on lumbar BMC and caused running to have a negative effect on tibial trabecular total tissue volume. Our study suggests that the LCHF diet impairs bone mass and some trabecular microstructure and reduces the benefit of exercise on lumbar BMC in old mice.

Acute Ketone Salts-Caffeine-Taurine-Leucine Supplementation but not Ketone Salts-Taurine-Leucine, Improves Endurance Cycling Performance

Coingestion of ketone salts, caffeine and the amino acids, taurine, and leucine improves endurance exercise performance. However, there is no study comparing this coingestion to the same nutrients without caffeine. We assessed whether ketone salts-caffeine-taurine-leucine (KCT) supplementation was superior to caffeine-free ketone salts-taurine-leucine supplementation (KT), or to an isoenergetic carbohydrate placebo (CHO-PLAC). Thirteen recreationally active men (mean ± SD: 177.5 ± 6.1 cm, 75.9 ± 4.6 kg, 23 ± 3 years, 12.0 ± 5.1% body fat) completed a best effort 20-km cycling time-trial, followed 15 min later by a Wingate power cycle test, after supplementing with either KCT (approximately 7 g of beta-hydroxybutyrate, approximately 120 mg of caffeine, 2.1 g of leucine, and 2.7 g of taurine), KT (i.e., same supplement without caffeine), or isoenergetic CHO-PLAC (11 g of dextrose). Blood ketones were elevated (p < .001) after ingestion of both KCT (0.65 ± 0.12 mmol/L) and KT (0.72 ± 0.31 mmol/L) relative to CHO-PLAC (0.06 ± 0.05 mmol/L). Moreover, KCT improved (p < .003) 20-km cycling time-trial performance (37.80 ± 2.28 min), compared with CHO-PLAC (39.40 ± 3.33 min) but not versus KT (38.75 ± 2.87 min; p < .09). 20-km cycling time-trial average power output was greater with KCT (power output = 180.5 ± 28.7 W) versus both KT (170.9 ± 31.7 W; p = .049) and CHO-PLAC (164.8 ± 34.7 W; p = .001). Wingate peak power output was also greater for both KCT (1,134 ± 137 W; p = .031) and KT (1,132 ± 128 W; p = .039) versus CHO-PLAC (1,068 ± 127 W). These data suggest that the observed improved exercise performance effects of this multi-ingredient supplement containing beta-hydroxybutyrate salts, taurine, and leucine are attributed partially to the addition of caffeine.

The Nutrition-Microbiota-Physical Activity Triad: An Inspiring New Concept for Health and Sports Performance

The human gut microbiota is currently the focus of converging interest in many diseases and sports performance. This review presents gut microbiota as a real “orchestra conductor” in the host’s physio(patho)logy due to its implications in many aspects of health and disease. Reciprocally, gut microbiota composition and activity are influenced by many different factors, such as diet and physical activity. Literature data have shown that macro- and micro-nutrients influence gut microbiota composition. Cumulative data indicate that gut bacteria are sensitive to modulation by physical activity, as shown by studies using training and hypoactivity models. Sports performance studies have also presented interesting and promising results. Therefore, gut microbiota could be considered a “pivotal” organ for health and sports performance, leading to a new concept: the nutrition-microbiota-physical activity triad. The next challenge for the scientific and medical communities is to test this concept in clinical studies. The long-term aim is to find the best combination of the three elements of this triad to optimize treatments, delay disease onset, or enhance sports performance. The many possibilities offered by biotic supplementation and training modalities open different avenues for future research.

What Is the Evidence That Dietary Macronutrient Composition Influences Exercise Performance? A Narrative Review

The introduction of the needle muscle biopsy technique in the 1960s allowed muscle tissue to be sampled from exercising humans for the first time. The finding that muscle glycogen content reached low levels at exhaustion suggested that the metabolic cause of fatigue during prolonged exercise had been discovered. A special pre-exercise diet that maximized pre-exercise muscle glycogen storage also increased time to fatigue during prolonged exercise. The logical conclusion was that the athlete's pre-exercise muscle glycogen content is the single most important acutely modifiable determinant of endurance capacity. Muscle biochemists proposed that skeletal muscle has an obligatory dependence on high rates of muscle glycogen/carbohydrate oxidation, especially during high intensity or prolonged exercise. Without this obligatory carbohydrate oxidation from muscle glycogen, optimum muscle metabolism cannot be sustained; fatigue develops and exercise performance is impaired. As plausible as this explanation may appear, it has never been proven. Here, I propose an alternate explanation. All the original studies overlooked one crucial finding, specifically that not only were muscle glycogen concentrations low at exhaustion in all trials, but hypoglycemia was also always present. Here, I provide the historical and modern evidence showing that the blood glucose concentration-reflecting the liver glycogen rather than the muscle glycogen content-is the homeostatically-regulated (protected) variable that drives the metabolic response to prolonged exercise. If this is so, nutritional interventions that enhance exercise performance, especially during prolonged exercise, will be those that assist the body in its efforts to maintain the blood glucose concentration within the normal range.

The Impact of a High-Carbohydrate/Low Fat vs. Low-Carbohydrate Diet on Performance and Body Composition in Physically Active Adults: A Cross-Over Controlled Trial

Background: Recently, high-carbohydrate or low-carbohydrate (HC/LC) diets have gained substantial popularity, speculated to improve physical performance in athletes; however, the effects of short-term changes of the aforementioned nutritional interventions remain largely unclear. Methods: The present study investigated the impact of a three-week period of HC/low-fat (HC) diet followed by a three-week wash-out-phase and subsequent LC diet on the parameters of physical capacity assessed via cardiopulmonary exercise testing, body composition via bioimpedance analysis and blood profiles, which were assessed after each of the respective diet periods. Twenty-four physically active adults (14 females, age 25.8 ± 3.7 years, body mass index 22.1 ± 2.2 kg/m2), of which six participants served as a control group, were enrolled in the study. Results: After three weeks of each diet, VO2peak was comparable following both interventions (46.8 ± 6.7 (HC) vs. 47.2 ± 6.7 mL/kg/min (LC; p = 0.58)) while a significantly higher peak performance (251 ± 43 W (HC) vs. 240 ± 45 W (LC); (p = 0.0001), longer time to exhaustion (14.5 ± 2.4 min (HC) vs. 14.1 ± 2.4 min (LC); p = 0.002) and greater Watt/kg performance (4.1 ± 0.5 W/kg (HC) vs. 3.9 ± 0.5 W/kg (LC); p = 0.003) was demonstrated after the HC diet. In both trial arms, a significant reduction in body mass (65.2 ± 11.2 to 63.8 ± 11.8 kg (HC) vs. 64.8 ± 11.6 to 63.5 ± 11.3 kg (LC); both p < 0.0001) and fat mass (22.7% to 21.2%; (HC) vs. 22.3% to 20.6% (LC); both p < 0.0001) but not in lean body mass or skeletal muscle mass was shown when compared to baseline. Resting metabolic rate was not different within both groups (p > 0.05). Total cholesterol and LDL-cholesterol significantly decreased after the HC diet (97.9 ± 33.6 mg/dL at baseline to 78.2 ± 23.5 mg/dL; p = 0.02) while triglycerides significantly increased (76 ± 38 mg/dL at baseline to 104 ± 44 mg/dL; p = 0.005). Conclusion: A short-term HC and LC diet showed improvements in various performance parameters in favor of the HC diet. Some parameters of body composition significantly changed during both diets. The HC diet led to a significant reduction in total and LDL-cholesterol while triglycerides significantly increased.

Exogenous Ketone Supplements in Athletic Contexts: Past, Present, and Future

The ketone bodies acetoacetate (AcAc) and β-hydroxybutyrate (βHB) have pleiotropic effects in multiple organs including brain, heart, and skeletal muscle by serving as an alternative substrate for energy provision, and by modulating inflammation, oxidative stress, catabolic processes, and gene expression. Of particular relevance to athletes are the metabolic actions of ketone bodies to alter substrate utilisation through attenuating glucose utilisation in peripheral tissues, anti-lipolytic effects on adipose tissue, and attenuation of proteolysis in skeletal muscle. There has been long-standing interest in the development of ingestible forms of ketone bodies that has recently resulted in the commercial availability of exogenous ketone supplements (EKS). These supplements in the form of ketone salts and ketone esters, in addition to ketogenic compounds such as 1,3-butanediol and medium chain triglycerides, facilitate an acute transient increase in circulating AcAc and βHB concentrations, which has been termed 'acute nutritional ketosis' or 'intermittent exogenous ketosis'. Some studies have suggested beneficial effects of EKS to endurance performance, recovery, and overreaching, although many studies have failed to observe benefits of acute nutritional ketosis on performance or recovery. The present review explores the rationale and historical development of EKS, the mechanistic basis for their proposed effects, both positive and negative, and evidence to date for their effects on exercise performance and recovery outcomes before concluding with a discussion of methodological considerations and future directions in this field.

Nutrition in Cycling

Cycling is predominantly an endurance sport in which fuel utilization for energy production relies on the availability and delivery of oxygen to exercising muscle. Nutrition and training interventions to improve endurance performance are continually evolving, but ultimately, prescription should aim to generate improvements in cycling power and velocity while prioritizing athlete health and well-being. The wide range of cycling events and the different environments in which events take place pose a variety of nutrition-related challenges for cyclists. This review addresses some of these challenges and highlights recent advancements in nutrition for cycling performance.

Nutritional approaches to counter performance constraints in high-level sports competition

New Findings

What is the topic of this review?

The nutritional strategies that athletes use during competition events to optimize performance and the reasons they use them.

What advances does it highlight?

A range of nutritional strategies can be used by competitive athletes, alone or in combination, to address various event‐specific factors that constrain event performance. Evidence for such practices is constantly evolving but must be combined with understanding of the complexities of real‐life sport for optimal implementation.

Abstract

High‐performance athletes share a common goal despite the unique nature of their sport: to pace or manage their performance to achieve the highest sustainable outputs over the duration of the event. Periodic or sustained decline in the optimal performance of event tasks, involves an interplay between central and peripheral phenomena that can often be reduced or delayed in onset by nutritional strategies. Contemporary nutrition practices undertaken before, during or between events include strategies to ensure the availability of limited muscle fuel stores. This includes creatine supplementation to increase muscle phosphocreatine content and consideration of the type, amount and timing of dietary carbohydrate intake to optimize muscle and liver glycogen stores or to provide additional exogenous substrate. Although there is interest in ketogenic low‐carbohydrate high‐fat diets and exogenous ketone supplements to provide alternative fuels to spare muscle carbohydrate use, present evidence suggests a limited utility of these strategies. Mouth sensing of a range of food tastants (e.g., carbohydrate, quinine, menthol, caffeine, fluid, acetic acid) may provide a central nervous system derived boost to sports performance. Finally, despite decades of research on hypohydration and exercise capacity, there is still contention around their effect on sports performance and the best guidance around hydration for sporting events. A unifying model proposes that some scenarios require personalized fluid plans while others might be managed by an ad hoc approach (ad libitum or thirst‐driven drinking) to fluid intake.

Nutritional ketosis is well-tolerated, even in type 1 diabetes: the ZeroFive100 Project; a proof-of-concept study

PURPOSE OF REVIEW

The objective of this study was to test the feasibility of exercising over a 5-day period while fasting, in those with and without type 1 diabetes mellitus (T1DM).Eight individuals, ages 29--62 years, two with T1DM, walked/ran around 20 miles per day for five consecutive days while only consuming water. All eight individuals completed the project with no physical injuries or problems with diabetes control. The blood glucose levels ranged from less than 3 mmol/l to 7 mmol/l in those without T1D, and less than 3 mmol/l to 9 mmol/l in those with T1D. The continuous glucose traces in those with T1D showed little variability in glucose levels. The participants without T1D had no symptoms from blood glucose under 3 mmol/l. Ketone levels ranged from 0.3 to 7.5 and the ketones for those with T1D were no different to ketones in those without T1D. The respiratory quotient was overwhelmingly in the fat-burning range. There was very little subjective hunger, nor did it negatively affect mood. In keto-adapted individuals, with or without T1DM, prolonged exercise for 5 days while in nutritional ketosis was feasible, and well tolerated.

RECENT FINDINGS

Eight adults, ages 28-62 years, trained for and completed a 5-day zero calorie fast covering 100 miles over 5 days. Training involved each individual preparing for the event according to their own programme. Typically, it involved both cardiovascular and strength training with the addition of practice water only fasts over 24-72 h or more based upon the individual's assessment of what was needed to complete the event. There was no formal protocol provided for this. The recommendation was that the participants would be keto adapted and trained to a level sufficient to complete the 5-day event. Keto adaptation was measured by ketone blood testing of betahydroxybutyrate. Two people had type 1 diabetes. All but one person was keto-adapted ahead of the event. All eight individuals completed the project with no physical injuries or problems with diabetes control. Prolonged fasting did neither lead to hunger nor did it negatively affect mood, which, if anything, was enhanced in most individuals. All keto-adapted people were shown to be burning fat stores throughout the 5 days, and everyone was measured to be in a state of nutritional ketosis. In type 1 diabetes, and ketones were in the same range as those without diabetes, insulin volumes were considerably reduced, and glucose control was close to physiological: nutritional ketosis is not a risk factor for diabetic ketoacidosis; consumption of sugar for energy is not required for distances of up to 100 miles in keto-adapted people; people who inject insulin do not necessarily need to consume carbohydrates unless rescuing a hypoglycaemic attack.

SUMMARY

The findings from this project should provide reassurance to those clinicians who want to provide the option of a ketogenic lifestyle to their patients with type 1 diabetes. They also confirm that the fat stores are available for aerobic respiration without apparent negative consequences on physical or mental function.

VIDEO ABSTRACT

http://links.lww.com/COE/A24.

Effects of 30 days of ketogenic diet on body composition, muscle strength, muscle area, metabolism, and performance in semi-professional soccer players

BACKGROUND

A ketogenic diet (KD) is a nutritional approach, usually adopted for weight loss, that restricts daily carbohydrates under 30 g/day. KD showed contradictory results on sport performance, whilst no data are available on team sports. We sought to investigate the influence of a KD on different parameters in semi-professional soccer players.

METHODS

Subjects were randomly assigned to a iso-protein (1.8 g/Kg body weight/day) ketogenic diet (KD) or western diet (WD) for 30 days. Body weight and body composition, resting energy expenditure (REE), respiratory exchange ratio (RER), cross sectional area (CSA) and isometric muscle strength of quadriceps, counter movement jump (CMJ) and yoyo intermittent recovery test time were measured.

RESULTS

There was a significantly higher decrease of body fat (p = 0.0359), visceral adipose tissue (VAT) (p = 0.0018), waist circumference (p = 0.0185) and extra-cellular water (p = 0.0060) in KD compared to WD group. Lean soft tissue, quadriceps muscle area, maximal strength and REE showed no changes in both groups. RER decreased significantly in KD (p = 0.0008). Yo-yo intermittent test improved significantly (p < 0.0001) in both groups without significant differences between groups. CMJ significantly improved (p = 0.0021) only in KD.

CONCLUSIONS

This is the first study investigating the effects of a KD on semi-professional soccer players. In our study KD athletes lost fat mass without any detrimental effects on strength, power and muscle mass. When the goal is a rapid weight reduction in such athletes, the use of a KD should be taken into account.

TRIAL REGISTRATION

registered retrospectively on Clinical Trial registration number NCT04078971 .

Recommendations and Nutritional Considerations for Female Athletes: Health and Performance

Optimal nutrition is an important aspect of an athlete’s preparation to achieve optimal health and performance. While general concepts about micro- and macronutrients and timing of food and fluids are addressed in sports science, rarely are the specific effects of women’s physiology on energy and fluid needs highly considered in research or clinical practice. Women differ from men not only in size, but in body composition and hormonal milieu, and also differ from one another. Their monthly hormonal cycles, with fluctuations in estrogen and progesterone, have varying effects on metabolism and fluid retention. Such cycles can change from month to month, can be suppressed with exogenous hormones, and may even be manipulated to capitalize on ideal timing for performance. But before such physiology can be manipulated, its relationship with nutrition and performance must be understood. This review will address general concepts regarding substrate metabolism in women versus men, common menstrual patterns of female athletes, nutrient and hydration needs during different phases of the menstrual cycle, and health and performance issues related to menstrual cycle disruption. We will discuss up-to-date recommendations for fueling female athletes, describe areas that require further exploration, and address methodological considerations to inform future work in this important area.

Effects of Combining a Ketogenic Diet with Resistance Training on Body Composition, Strength, and Mechanical Power in Trained Individuals: A Narrative Review

Ketogenic diets (KD) have gained popularity in recent years among strength-trained individuals. The present review summarizes current evidence—with a particular focus on randomized controlled trials—on the effects of KD on body composition and muscle performance (strength and power output) in strength-trained individuals. Although long-term studies (>12 weeks) are lacking, growing evidence supports the effectiveness of an ad libitum and energy-balanced KD for reducing total body and fat mass, at least in the short term. However, no or negligible benefits on body composition have been observed when comparing hypocaloric KD with conventional diets resulting in the same energy deficit. Moreover, some studies suggest that KD might impair resistance training-induced muscle hypertrophy, sometimes with concomitant decrements in muscle performance, at least when expressed in absolute units and not relative to total body mass (e.g., one-repetition maximum). KD might therefore be a beneficial strategy for promoting fat loss, although it might not be a recommendable option to gain muscle mass and strength/power. More research is needed on the adoption of strategies for avoiding the potentially detrimental effect of KD on muscle mass and strength/power (e.g., increasing protein intake, reintroduction of carbohydrates before competition). In summary, evidence is as yet scarce to support a major beneficial effect of KD on body composition or performance in strength-trained individuals. Furthermore, the long-term effectiveness and safety of this type of diet remains to be determined.