Is exercise best served on an empty stomach?

Understanding the variation in exercise responses to guide personalized physical activity prescriptions

Understanding the factors that contribute to exercise response variation is the first step in achieving the goal of developing personalized exercise prescriptions. This review discusses the key molecular and other mechanistic factors, both extrinsic and intrinsic, that influence exercise responses and health outcomes. Extrinsic characteristics include the timing and dose of exercise, circadian rhythms, sleep habits, dietary interactions, and medication use, whereas intrinsic factors such as sex, age, hormonal status, race/ethnicity, and genetics are also integral. The molecular transducers of exercise (i.e., genomic/epigenomic, proteomic/post-translational, transcriptomic, metabolic/metabolomic, and lipidomic elements) are considered with respect to variability in physiological and health outcomes. Finally, this review highlights the current challenges that impede our ability to develop effective personalized exercise prescriptions. The Molecular Transducers of Physical Activity Consortium (MoTrPAC) aims to fill significant gaps in the understanding of exercise response variability, yet further investigations are needed to address additional health outcomes across all populations.

Morning exercise and pre-breakfast metformin interact to reduce glycaemia in people with type 2 diabetes: a randomized crossover trial

Exercise is recommended in the treatment of type 2 diabetes and can improve insulin sensitivity. However, previous evidence suggests that exercise at different times of the day in people with type 2 diabetes may have opposing outcomes on glycaemia. Metformin is the most commonly prescribed initial pharmacological intervention in type 2 diabetes, and may alter adaptions to exercise. It is unknown if there is an interaction between metformin and diurnal exercise outcomes. We aimed to investigate glycaemic outcomes of moderate intensity morning vs. evening exercise in people with type 2 diabetes being prescribed metformin monotherapy. In this study, nine males and nine females with type 2 diabetes undergoing metformin monotherapy (age 61 ± 8.2 years, mean ± SD) completed a 16-week crossover trial including 2-week baseline recording, 6 weeks randomly assigned to a morning exercise (07.00-10.00 h) or evening exercise (16.00-19.00 h) and a 2-week wash-out period. Exercise arms consisted of 30 min of walking at 70% of estimated max heart rate every other day. Glucose levels were measured with continuous glucose monitors and activity measured by wrist-worn monitors. Food-intake was recorded by 4-day food diaries during baseline, first and last 2 weeks of each exercise arm. There was no difference in exercise intensity, total caloric intake or total physical activity between morning and evening arms. As primary outcomes, acute (24 h) glucose area under the curve (AUC), was lower (P = 0.02) after acute morning exercise (180.6 ± 68.4 mmol/l) compared to baseline (210.3 ± 76.7 mmol/l); and there were no differences identified for glucose (mmol/l) between baseline, morning and evening exercise at any specific time point when data were analysed with two-way ANOVA. As secondary outcomes, acute glucose AUC was significantly lower (P = 0.01) in participants taking metformin before breakfast (152.5 ± 29.95 mmol/l) compared with participants taking metformin after breakfast (227.2 ± 61.51 mmol/l) only during the morning exercise arm; and during weeks 5-6 of the exercise protocol, glucose AUC was significantly lower (P = 0.04) for participants taking metformin before breakfast (168.8 ± 15.8 mmol/l), rather than after breakfast (224.5 ± 52.0 mmol/l), only during morning exercise. Our data reveal morning moderate exercise acutely lowers glucose levels in people with type 2 diabetes being prescribed metformin. This difference appears to be driven by individuals that consumed metformin prior to breakfast rather than after breakfast. This beneficial effect upon glucose levels of combined morning exercise and pre-breakfast metformin persisted through the final 2 weeks of the trial. Our findings suggest that morning moderate intensity exercise combined with pre-breakfast metformin intake may benefit the management of glycaemia in people with type 2 diabetes. KEY POINTS: Morning moderate exercise acutely lowers glucose levels in people with type 2 diabetes being prescribed metformin. This difference appears to be driven by individuals that consumed metformin prior to breakfast rather than after breakfast. Morning exercise combined with pre-breakfast metformin persistently reduced glucose compared to morning exercise combined with post-breakfast metformin through the final week (week 6) of the intervention. Our study suggests it may be possible to make simple changes to the time that people with type 2 diabetes take metformin and perform exercise to improve their blood glucose.

The Effects of Six Weeks of Fasted Aerobic Exercise on Body Shape and Blood Biochemical Index in Overweight and Obese Young Adult Males

BACKGROUND/OBJECTIVE

The effects of fasted aerobic exercise on body composition and whether it causes adverse effects remain controversial. This study was to compare the effects of fasted and non-fasted aerobic exercise on body shape and blood biochemical indexes in overweight and obese young adult males, and observe whether FAE triggers adverse reactions.

METHODS

Thirty overweight and obese young adult males were randomly divided into fasted aerobic exercise (FAE) group, non-fasted aerobic exercise (NFAE) group, and control group. They were subjected to indoor treadmill intervention five days a week combined with diet control for six weeks. The FAE group had breakfast 0.5 h after exercise, and the NFAE group exercised 1 h after breakfast. Both groups filled out adverse reaction questionnaires during exercise, and the control group did not have any intervention. Height, weight, body mass index (BMI), and body fat percentage of the three groups of subjects before and after the experiment were measured by the GAIA KIKO bio-resistance antibody composition analyzer in Korea; waist circumference (WC), hip circumference (HC), waist-to-hip ratio (WHR), and waist-to-height ratio (WHtR) were measured by the tape measure method; fasting plasma glucose (FPG), fasting insulin (FINs), total cholesterol (TC), triglyceride (TG), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), very low density lipoprotein (VLDL), and HDL-C/LDL-C were measured by Roche C8000 automatic biochemical analysis instrument.

RESULTS

Weight, BMI, body fat percentage, WC, HC, WHR, WHtR, TG, TC, LDL-C and VLDL decreased very significantly (P < 0.01) in the FAE and NFAE groups after the 6-week experiment. The decrease in FINS was significant in the FAE group (P < 0.05) and the decrease in HDL-C was very significant in the NFAE group (P < 0.01). There was no significant difference in the frequency of adverse reactions between two groups (P > 0.05).

CONCLUSION

Six-week FAE and NFAE significantly improved body shape in overweight and obese young adult males, while FAE significantly reduced fasting insulin levels and increased tissue cell sensitivity to insulin. And compared to NFAE, 30 min of FAE in the morning did not increase adverse effects.

Acute/Chronic Responses of Combined Training on Serum Pro-thermogenic/Anti-inflammatory Inducers and Its Relation With Fed and Fasting State in Overweight Type 2 Diabetic Individuals

Concentrations of pro-thermogenic/anti-inflammatory inductors are influenced by fed/fasting, sedentary/trained states, and metabolic pattern. However, there is a lack of information on the interactions of these conditions, especially in humans. Thus, the present study aimed to evaluate the chronic and acute training responses as well as the fed/fasted states of serum pro-thermogenic/anti-inflammatory inducers in overweight type 2 diabetics individuals. Fifteen individuals with type 2 diabetes [body mass index (BMI): 29.61 ± 3.60 kg/m2; age: 50.67 ± 3.97 years] participated in the study. In the pre- and post-experimental periods, baseline clinical parameters analyses were performed. Pro-thermogenic/anti-inflammatory inductors were evaluated pre/post-baseline and before, shortly after, and after 30′ and 60′ in the first and last sessions of a 16-week combined training (CT) period. These inducers were also compared for fasting and feeding before and after the training period. CT has improved baseline physical fitness, metabolic pattern, and it has also increased interleukin (IL)33 and FNDC5/irisin. In the first training session, there was a decrease in IL4, IL13, and IL33, besides an increase in FNDC5/irisin, and natriuretic peptides. In the last training session, there was an increase in natriuretic peptides and bone morphogenic protein 4 (BMP4). Differences in responses between the first and last training sessions were observed at certain post-session times for IL4, IL33, and natriuretic peptides, always with higher concentrations occurring in the last session. In evaluating the area under the curve (AUC) of the first and last training session, FNDC5/irisin, natriuretics peptides, and meteorin-like showed increased areas in the last training session. The pre-training fed state showed an increase in IL4 and IL33, while in fasting there was an increase in meteorin-like, natriuretic peptides, and FNDC5/irisin. In the post-training, IL4, IL13, and IL33 were increased in the fed state, while meteorin-like, natriuretic peptides, and FNDC5/irisin remained increased in the fast. Adaptation to physical training and a better metabolic pattern favor an improvement in the acute secretory pattern in part of pro-thermogenic and anti-inflammatory substances analyzed. The fed and fasting states also interfere differently in these substances, where fasting interferes with the increase of myokines, while the fed state induces an increase in interleukins.

Clinical Trial Registration: [http://www.ensaiosclinicos.gov.br/rg/RBR-62n5qn/], identifier [U1111-1202-1476].

Fasting and Exercise in Oncology: Potential Synergism of Combined Interventions

Nutrition and exercise interventions are strongly recommended for most cancer patients; however, much debate exists about the best prescription. Combining fasting with exercise is relatively untouched within the oncology setting. Separately, fasting has demonstrated reductions in chemotherapy-related side effects and improved treatment tolerability and effectiveness. Emerging evidence suggests fasting may have a protective effect on healthy cells allowing chemotherapy to exclusively target cancer cells. Exercise is commonly recommended and attenuates treatment- and cancer-related adverse changes to body composition, quality of life, and physical function. Given their independent benefits, in combination, fasting and exercise may induce synergistic effects and further improve cancer-related outcomes. In this narrative review, we provide a critical appraisal of the current evidence of fasting and exercise as independent interventions in the cancer population and discuss the potential benefits and mechanisms of combined fasting and exercise on cardiometabolic, body composition, patient-reported outcomes, and cancer-related outcomes. Our findings suggest that within the non-cancer population combined fasting and exercise is a viable strategy to improve health-related outcomes, however, its safety and efficacy in the oncology setting remain unknown. Therefore, we also provide a discussion on potential safety issues and considerations for future research in the growing cancer population.

Low-intensity exercise stimulates bioenergetics and increases fat oxidation in mitochondria of blood mononuclear cells from sedentary adults

AIM

Exercise training induces adaptations in muscle and other tissue mitochondrial metabolism, dynamics, and oxidative phosphorylation capacity. Mitochondrial fatty acid oxidation was shown to be pivotal for the anti-inflammatory status of immune cells. We hypothesize that exercise training can exert effects influence mitochondrial fatty acid metabolism in peripheral blood mononuclear cells (PBMCs). The aim was to investigate the effect of exercise on the fatty acid oxidation-dependent respiration in PBMCs.

DESIGN

Twelve fasted or fed volunteers first performed incremental-load exercise tests to exhaustion on a cycle ergometer to determine the optimal workload ensuring maximal health benefits in volunteers with a sedentary lifestyle. In addition, the same volunteers performed 60 min of low-intensity constant-load exercise.

RESULTS

In the incremental-load exercise, the maximal whole-body fat oxidation rate measured by indirect calorimetry was reached at the fasted state already at a 50 W workload. At the 75-175 W workloads, the contribution of fat oxidation significantly decreased to only 11%, the heart rate increased to 185 BPM, and the study participants reached exhaustion. These results show that low-intensity exercise (50W) is optimal for maximal whole-body fat utilization. After low-intensity exercise, the ROUTINE mitochondrial respiration, as well as fatty acid oxidation-dependent respiration in PBMCs at LEAK and OXPHOS states, were significantly increased by 31%, 65%, and 76%, respectively. In addition, during 60 min of low-intensity (50W) exercise, a 2-fold higher lipolysis rate was observed and 13.5 ± 0.9 g of fat was metabolized, which was 57% more than the amount of fat that was metabolized during the incremental-load exercise.

CONCLUSIONS

In individuals with a sedentary lifestyle participating in a bicycle ergometry exercise program, maximal lipolysis and whole-body fat oxidation rate is reached in a fasted state during low-intensity exercise. For the first time, it was demonstrated that low-intensity exercise improves bioenergetics and increases fatty acid oxidation in PBMCs and may contribute to the anti-inflammatory phenotype.

High-Intensity Interval Exercise Performance and Short-Term Metabolic Responses to Overnight-Fasted Acute-Partial Sleep Deprivation

People practicing high-intensity interval exercise (HIIE) fasted during the morning hours under a lack of sleep. Such a habit may jeopardize the health benefits related to HIIE and adequate sleep. Fifteen habitually good sleeper males (age 31.1 ± 5.3 SD year) completed on a treadmill two isocaloric (500 kcal) HIIE sessions (3:2 min work:rest) averaged at 70% VO2reserve after 9-9.5 h of reference sleep exercise (RSE) and after 3-3.5 h of acute-partial sleep deprivation exercise (SSE). Diet and sleep patterns were controlled both 1 week prior and 2 days leading up to RSE and SSE. HIIE related performance and substrate utilization data were obtained from the continuous analysis of respiratory gases. Data were analyzed using repeated measures ANOVA with the baseline maximum oxygen uptake (VO2max) and body fat percentage (BF%) as covariates at p < 0.05. No difference was observed in VO2max, time to complete the HIIE, VE, RER, CHO%, and FAT% utilization during the experimental conditions. Whether attaining an adequate amount of sleep or not, the fasted HIIE performance and metabolism were not affected. We propose to practice the fasted HIIE under adequate sleep to receive the pleiotropic beneficial effects of sleep to the human body.

Does exercising before or after a meal affect energy balance in adolescents with obesity?

BACKGROUND AND AIM

Exercise timing has been suggested to affect appetite and energy intake (EI). The aim of this study was to examine the impact of exercising immediately before or after a meal on EI, appetite sensations and food reward (FR) in adolescents with obesity.

METHODS AND RESULTS

Seventeen adolescents with obesity completed 3 experimental sessions (randomized controlled trial): rest + lunch (CON); exercise + lunch (EX-MEAL); lunch + exercise (MEAL-EX). The exercise consisted of cycling 30 min at 65%V̇O_2peak. Outcomes included ad libitum EI (weighed lunch and dinner), FR (Leeds Food Preference Questionnaire at pre- and post-combination of exercise/rest and lunch, and pre-dinner) and appetite sensations (visual analogue scales). EI was not different between conditions. Compared with CON, relative EI at lunch was lower in EX-MEAL and MEAL-EX (p ≤ 0.05) and daily only in MEAL-EX (p < 0.01). Postprandial fullness was higher in EX-MEAL compared to CON. Compared with CON, both EX-MEAL and MEAL-EX attenuated the increase in wanting for sweet food and reduced explicit liking for fat.

CONCLUSIONS

These preliminary results suggest that exercising immediately before or after a meal produce few differences in appetite and have small beneficial effects on overall energy balance in adolescents with obesity, as well as on FR.

CLINICAL TRIALS

NCT03967782.

Lipid Metabolism Links Nutrient-Exercise Timing to Insulin Sensitivity in Men Classified as Overweight or Obese

CONTEXT

Pre-exercise nutrient availability alters acute metabolic responses to exercise, which could modulate training responsiveness.

OBJECTIVE

To assess acute and chronic effects of exercise performed before versus after nutrient ingestion on whole-body and intramuscular lipid utilization and postprandial glucose metabolism.

DESIGN

(1) Acute, randomized, crossover design (Acute Study); (2) 6-week, randomized, controlled design (Training Study).

SETTING

General community.

PARTICIPANTS

Men with overweight/obesity (mean ± standard deviation, body mass index: 30.2 ± 3.5 kg⋅m-2 for Acute Study, 30.9 ± 4.5 kg⋅m-2 for Training Study).

INTERVENTIONS

Moderate-intensity cycling performed before versus after mixed-macronutrient breakfast (Acute Study) or carbohydrate (Training Study) ingestion.

RESULTS

Acute Study-exercise before versus after breakfast consumption increased net intramuscular lipid utilization in type I (net change: -3.44 ± 2.63% versus 1.44 ± 4.18% area lipid staining, P < 0.01) and type II fibers (-1.89 ± 2.48% versus 1.83 ± 1.92% area lipid staining, P < 0.05). Training Study-postprandial glycemia was not differentially affected by 6 weeks of exercise training performed before versus after carbohydrate intake (P > 0.05). However, postprandial insulinemia was reduced with exercise training performed before but not after carbohydrate ingestion (P = 0.03). This resulted in increased oral glucose insulin sensitivity (25 ± 38 vs -21 ± 32 mL⋅min-1⋅m-2; P = 0.01), associated with increased lipid utilization during exercise (r = 0.50, P = 0.02). Regular exercise before nutrient provision also augmented remodeling of skeletal muscle phospholipids and protein content of the glucose transport protein GLUT4 (P < 0.05).

CONCLUSIONS

Experiments investigating exercise training and metabolic health should consider nutrient-exercise timing, and exercise performed before versus after nutrient intake (ie, in the fasted state) may exert beneficial effects on lipid utilization and reduce postprandial insulinemia.

Exercise Training and Fasting: Current Insights

Fasting is defined as the abstinence from consuming food and/or beverages for different periods of time. Both traditional and modern healthcare systems recommend fasting as a therapeutic intervention for the management of several chronic, non-infectious diseases. Exercising during a fasting state increases lipolysis in adipose tissue while also stimulating peripheral fat oxidation, resulting in increased fat utilization and weight loss. A key focus of this review is to assess whether endurance training performed while fasting induces specific training adaptations, where increased fat oxidation improves long-term endurance levels. Fasting decreases body weight, lean body and fat content in both trained and untrained individuals. Several studies indicate a broader impact of fasting on metabolism, with effects on protein and glucose metabolism in sedentary and untrained subjects. However, there are conflicting data regarding the effects of fasting on glucose metabolism in highly trained athletes. The effects of fasting on physical performance indicators also remain unclear, with some reporting a decreased performance, while others found no significant effects. Differences in experimental design, severity of calorie restriction, duration, and participant characteristics could, at least in part, explain such discordant findings. Our review of the literature suggests that there is little evidence to support the notion of endurance training and fasting-mediated increases in fat oxidation, and we recommend that endurance athletes should avoid high intensity training while fasting.

Carbohydrate Restriction in Type 1 Diabetes: A Realistic Therapy for Improved Glycaemic Control and Athletic Performance?

Around 80% of individuals with Type 1 diabetes (T1D) in the United States do not achieve glycaemic targets and the prevalence of comorbidities suggests that novel therapeutic strategies, including lifestyle modification, are needed. Current nutrition guidelines suggest a flexible approach to carbohydrate intake matched with intensive insulin therapy. These guidelines are designed to facilitate greater freedom around nutritional choices but they may lead to higher caloric intakes and potentially unhealthy eating patterns that are contributing to the high prevalence of obesity and metabolic syndrome in people with T1D. Low carbohydrate diets (LCD; <130 g/day) may represent a means to improve glycaemic control and metabolic health in people with T1D. Regular recreational exercise or achieving a high level of athletic performance is important for many living with T1D. Research conducted on people without T1D suggests that training with reduced carbohydrate availability (often termed "train low") enhances metabolic adaptation compared to training with normal or high carbohydrate availability. However, these "train low" practices have not been tested in athletes with T1D. This review aims to investigate the known pros and cons of LCDs as a potentially effective, achievable, and safe therapy to improve glycaemic control and metabolic health in people with T1D. Secondly, we discuss the potential for low, restricted, or periodised carbohydrate diets in athletes with T1D.

Nutrient–nutrient interactions: competition, bioavailability, mechanism and function in health and diseases

The Nutrition Society Spring Conference 2018, held in Glasgow, brought together experts focusing on the interaction between different nutrients and how this impacts absorption, metabolism and health from biochemical and physiological perspectives. This cross-cutting theme was examined from a range of perspectives, bringing together experts on topics ranging from food processing to the impact of inflammation on nutrient status. Two plenary lectures provided a food landscape and lifecourse background to the proceedings, with on the first day a focus on processed/ultra-processed foods and their nutrient composition and, on the second day, a plenary lecture exploring the role that nutrient–nutrient interactions within the maternal diet have for the lifelong health of the offspring. The meeting was framed around three symposia, examining the competition and bioavailability of dietary components, nutrient–nutrient interactions and their role in protection from chronic diseases and the mechanisms of nutrient–nutrient interactions. The meeting ended with a round table, and an overall conclusion highlighting the opportunities to derive further understanding of the short- and long-term implications of diets through the study of nutrient–nutrient interactions.