The effect of acute manipulation of carbohydrate availability on high intensity running performance, running economy, critical speed, and substrate metabolism in trained Male runners

Completing selected training sessions with reduced glycogen availability is associated with greater signalling and improved muscle oxidative capacity, although it may impact the overall quality of the session. We examined the effects of low carbohydrate availability on high intensity exercise performance, running economy, critical speed, and substrate metabolism. On two occasions, nine male runners (V̇O2peak 60.3 ± 3.3 mL.kg-1.min-1) completed a glycogen depletion protocol involving 90-min at 75%vV̇O2peak followed by 10 × 1-min at 110% vV̇O2peak. This was followed either by high (HIGH) or low (LOW) carbohydrate intake (>6 g.kg-1.day-1 and <50 g.day-1, respectively) until completion of a performance protocol on day 2 consisting of a series of time-trials (TT) (50m to 3000m) and physiological assessments. There were no differences between LOW and HIGH for any TT distance (mean TT performance times for LOW and HIGH were: 3000m TT 651.7 ± 52.8s and 646.4 ± 52.5s, 1500 m TT 304.0 ± 20.2s and 304.2 ± 22.1s, 400 m TT 67.64 ± 4.2s and 67.3 ± 3.8s, 50 m TT 7.27 ± 0.44s and 7.25 ± 0.45s, respectively, P > 0.05), though some athletes performed better in LOW (n = 5). While fat oxidation in LOW was significantly greater than HIGH (Δ0.32 ± 0.14 g.min-1; P < 0.001 at 14 km.h-1 and Δ0.34 ± 0.12 g.min-1 at 16 km.h-1; P < 0.01), running economy did not differ between trials (P > 0.05). Acute manipulation of carbohydrate availability showed immediate effects on substrate metabolism evidenced by greater fat oxidation without changes in RE. Acute low carbohydrate availability did not affect high intensity running performance across a range of distances.Highlights Acute manipulation of muscle glycogen availability using an exercise and dietary manipulation protocol did not affect subsequent high intensity running performance across a range of running distances.Reduced muscle glycogen resulted in a marked increase in fat oxidation in low glycogen condition but no changes in running economy or critical speed.Individual factors should be considered when prescribing high intensity sessions with restricted carbohydrate availability.

Carbohydrate intake before and during high intensity exercise with reduced muscle glycogen availability affects the speed of muscle reoxygenation and performance

Muscle glycogen state and carbohydrate (CHO) supplementation before and during exercise may impact responses to high-intensity interval training (HIIT). This study determined cardiorespiratory, substrate metabolism, muscle oxygenation, and performance when completing HIIT with or without CHO supplementation in a muscle glycogen depleted state. On two occasions, in a cross-over design, eight male cyclists performed a glycogen depletion protocol prior to HIIT during which either a 6% CHO drink (60 g.hr^-1) or placebo (%CHO, PLA) was consumed. HIIT consisted of 5 × 2 min at 80% peak power output (PPO), 3 × 10-min bouts of steady-state (SS) cycling (50, 55, 60% PPO), and a time-to-exhaustion (TTE) test. There was no difference in SS [Formula: see text], HR, substrate oxidation and gross efficiency (GE %) between CHO and PLA conditions. A faster rate of muscle reoxygenation (%. s^-1) existed in PLA after the 1st (Δ - 0.23 ± 0.22, d = 0.58, P < 0.05) and 3rd HIIT intervals (Δ - 0.34 ± 0.25, d = 1.02, P < 0.05). TTE was greater in CHO (7.1 ± 5.4 min) than PLA (2.5 ± 2.3 min, d = 0.98, P < 0.05). CHO consumption before and during exercise under reduced muscle glycogen conditions did not suppress fat oxidation, suggesting a strong regulatory role of muscle glycogen on substrate metabolism. However, CHO ingestion provided a performance benefit under intense exercise conditions commenced with reduced muscle glycogen. More research is needed to understand the significance of altered muscle oxygenation patterns during exercise.

A 12-week, whole-food carbohydrate-restricted feasibility study in overweight children

Background: Childhood obesity is a global health concern. Conventional nutrition guidelines have come under scrutiny in helping to achieve long-term healthy weight. An alternative carbohydrate-restricted, higher fat approach has shown to be effective in adults, but research is limited in youth. Aim: To assess the feasibility of a 12-week whole-food, carbohydrate-restricted diet on weight loss and metabolic health. Setting: Overweight children aged 8–13 years. Methods: In this single-arm study, 25 overweight children were provided with whole-food, carbohydrate-restricted dietary guidelines. Primary outcomes – dietary acceptability, adherence and affordability – were assessed qualitatively weekly (telephone) and post-intervention (focus groups). Secondary outcomes – Body mass index (BMI), waist circumference, lipids and glycaemic control measures – were assessed at 0 and 12 weeks. Change scores were analysed using the t-statistic and interpreted using the statistical significance threshold, p < 0.05. Results: Overall, dietary acceptability was mostly positive, and reports of affordability by parents were mixed. Attrition rates were high (48%); adherence was influenced, positively and negatively, by levels of support from friends and family. Completing children reduced BMI by 2.1 ± 1.5 kg.m2 (p < 0.05). Key blood parameter changes included a reduction in triglycerides (−0.17 ± 0.48 mmol/L; p = 0.242) and an increase in high-density lipoprotein (HDL) cholesterol (0.24 ± 0.19 mmol/L; p < 0.05). Conclusion: Children achieved some weight loss and health outcome success using this dietary approach. For sustainable weight loss maintenance, full family and health professional support, particularly on a more intensive level at the start, may be required.

The Effect of Medium Chain Triglycerides on Time to Nutritional Ketosis and Symptoms of Keto-Induction in Healthy Adults: A Randomised Controlled Clinical Trial

Medium chain triglycerides (MCTs) are ketogenic and might reduce adverse effects of keto-induction and improve time to ketosis and the tolerability of very low carbohydrate diets. This study investigates whether MCT supplementation improves time to nutritional ketosis (NK), mood, and symptoms of keto-induction. We compared changes in beta-hydroxybutyrate (BOHB), blood glucose, symptoms of keto-induction, and mood disturbance, in 28 healthy adults prescribed a ketogenic diet, randomised to receive either 30 ml of MCT, or sunflower oil as a control, three times per day, for 20 days. The primary outcome measured was the achievement of NK (≥0.5 mmol·L-1 BOHB). Participants also completed a daily Profile of Mood States and keto-induction symptom questionnaire. MCT resulted in higher BOHB at all time points and faster time to NK, a result that failed to reach significance. Symptoms of keto-induction resulted from both diets, with a greater magnitude in the control group, except for abdominal pain, which occurred with greater frequency and severity in the MCT-supplemented diet. There was a possibly beneficial effect on symptoms by MCT, but the effect on mood was unclear. Based on these results, MCTs increase BOHB compared with LCT and reduce symptoms of keto-induction. It is unclear whether MCTs significantly improve mood or time to NK. The trial was registered by the Australia New Zealand Clinical Trial Registry ACTRN12616001099415.

The use of nutritional supplements to induce ketosis and reduce symptoms associated with keto-induction: a narrative review

Background

Adaptation to a ketogenic diet (keto-induction) can cause unpleasant symptoms, and this can reduce tolerability of the diet. Several methods have been suggested as useful for encouraging entry into nutritional ketosis (NK) and reducing symptoms of keto-induction. This paper reviews the scientific literature on the effects of these methods on time-to-NK and on symptoms during the keto-induction phase.

Methods

PubMed, Science Direct, CINAHL, MEDLINE, Alt Health Watch, Food Science Source and EBSCO Psychology and Behavioural Sciences Collection electronic databases were searched online. Various purported ketogenic supplements were searched along with the terms “ketogenic diet”, “ketogenic”, “ketosis” and ketonaemia (/ ketonemia). Additionally, author names and reference lists were used for further search of the selected papers for related references.

Results

Evidence, from one mouse study, suggests that leucine doesn’t significantly increase beta-hydroxybutyrate (BOHB) but the addition of leucine to a ketogenic diet in humans, while increasing the protein-to-fat ratio of the diet, doesn’t reduce ketosis. Animal studies indicate that the short chain fatty acids acetic acid and butyric acid, increase ketone body concentrations. However, only one study has been performed in humans. This demonstrated that butyric acid is more ketogenic than either leucine or an 8-chain monoglyceride. Medium-chain triglycerides (MCTs) increase BOHB in a linear, dose-dependent manner, and promote both ketonaemia and ketogenesis. Exogenous ketones promote ketonaemia but may inhibit ketogenesis.

Conclusions

There is a clear ketogenic effect of supplemental MCTs; however, it is unclear whether they independently improve time to NK and reduce symptoms of keto-induction. There is limited research on the potential for other supplements to improve time to NK and reduce symptoms of keto-induction. Few studies have specifically evaluated symptoms and adverse effects of a ketogenic diet during the induction phase. Those that have typically were not designed to evaluate these variables as primary outcomes, and thus, more research is required to elucidate the role that supplementation might play in encouraging ketogenesis, improve time to NK, and reduce symptoms associated with keto-induction.

A 12-week low-carbohydrate, high-fat diet improves metabolic health outcomes over a control diet in a randomised controlled trial with overweight defence force personnel

Overweight, obesity, and poor health is becoming a global concern for defence force personnel. Conventional nutrition guidelines are being questioned for their efficacy in achieving optimal body composition and long-term health. This study compared the effects of a 12-week low-carbohydrate, high-fat diet with a conventional, high-carbohydrate, low-fat diet on weight reduction and metabolic health outcomes in at-risk New Zealand Defence Force personnel. In this randomised controlled trial, 41 overweight personnel were assigned to intervention and control groups. Weight, waist circumference, fasting lipids, and glycaemic control were assessed at baseline and at 12 weeks. Within-group change scores were analysed using the t statistic and interpreted using a p < 0.05 level of statistical significance. Between-group mean differences and confidence intervals were analysed using effect sizes and magnitude-based inferences. Twenty-six participants completed the trial (14 intervention, 12 control). Both groups showed statistically significant weight and waist circumference reductions; the intervention group significantly reduced triglycerides and serum glucose and significantly increased high-density lipoprotein cholesterol (HDLc). Relative to control, the intervention group showed small, possibly to likely beneficial effects for weight, triglycerides, glucose, insulin, and homeostasis model assessment of insulin resistance; moderate, likely beneficial effects for HDL cholesterol, triglyceride:HDLc ratio and HbA1c; and a small, likely harmful effect for low-density lipoprotein cholesterol. This dietary approach shows promise for short-term weight loss and improved metabolic health outcomes conditions compared with mainstream recommendations. It should be offered to defence force personnel at least as a viable alternative means to manage their weight and health.

Do health behaviours cluster in a working population in New Zealand?

ISSUE ADDRESSED

This study examines whether adhering to healthy weight, physical activity and fruit and vegetable recommendations lead to a cluster in a working population.

METHODS

An online Health Risk Assessment (HRA) was administered to 1,296 (36%) employees in nine organisations across New Zealand. Clustering was defined as the co-prevalence of behaviours above that which was expected by the laws of probability.

RESULTS

Less than half the participants met physical activity guidelines (44.5%) or maintained a healthy weight (46.7%), and 29.4% consumed five or more servings of fruit and vegetables per day. Just 3.8% of participants met all three recommendations, compared to an expected prevalence of 7.6%. There was no clustering of health behaviours, with no difference between expected and observed prevalence (with an observed/expected (O/E) ratio between 0.68-0.93).

CONCLUSION

Few people adhere to two or more simple public health messages recommended to reduce risk of chronic disease.

Exploring the relationship between sugars and obesity

Objective

Investigate the relationship between body mass index (BMI) and intake of sugars and fat in New Zealand adults and children.

Design

Secondary analyses of National Nutrition Survey (1997) and Children’s Nutrition Survey (2002) data for the New Zealand population. BMI calculated from height and weight; fat, sugars and sucrose (used as a surrogate for added sugars) intakes estimated from 24-hour diet recall. Ethnic-specific analyses of children’s data. Relationships (using linear regression) between BMI and sugars/sucrose intakes; per cent total energy from fat; mean total energy intake from sucrose. Subjects classified into diet-type groups by levels of intake of fat and sucrose; relative proportions of overweight/obese children in each group compared with that of normal weight subjects using design-adjusted χ2 tests.

Setting

New Zealand homes and schools.

Subjects

4379 adults (15+ years); 3049 children (5–14 years).

Results

Sugars (but not sucrose) intake was significantly lower among obese compared to normal weight children. In adults and children, those with the lowest intake of sugars from foods were significantly more likely to be overweight/obese. Sucrose came predominantly from beverages; in children, 45% of this was from powdered drinks. Sucrose intake from sugary beverages was not related to BMI. Per cent total energy (%E) from sucrose was significantly inversely related to %E from fat among adults and children. Proportions of overweight/obese adults or children in each diet-type group did not differ from that of normal weight individuals.

Conclusions

Current sugars or sucrose intake is not associated with body weight status in the New Zealand population.