Carbohydrate Availability as a Regulator of Energy Balance With Exercise

Impaired metabolic flexibility to fasting is associated with increased ad libitum energy intake in healthy adults

OBJECTIVE

We investigated how changes in 24-h respiratory exchange ratio (RER) and substrate oxidation during fasting versus an energy balance condition influence subsequent ad libitum food intake.

METHODS

Forty-four healthy, weight-stable volunteers (30 male and 14 female; mean [SD], age 39.3 [11.0] years; BMI 31.7 [8.3] kg/m2) underwent 24-h energy expenditure measurements in a respiratory chamber during energy balance (50% carbohydrate, 30% fat, and 20% protein) and 24-h fasting. Immediately after each chamber stay, participants were allowed 24-h ad libitum food intake from computerized vending machines.

RESULTS

Twenty-four-hour RER decreased by 9.4% (95% CI: -10.4% to -8.5%; p < 0.0001) during fasting compared to energy balance, reflecting a decrease in carbohydrate oxidation (mean [SD], -2.6 [0.8] MJ/day; p < 0.0001) and an increase in lipid oxidation (2.3 [0.9] MJ/day; p < 0.0001). Changes in 24-h RER and carbohydrate oxidation in response to fasting were correlated with the subsequent energy intake such that smaller decreases in fasting 24-h RER and carbohydrate oxidation, but not lipid oxidation, were associated with greater energy intake after fasting (r = 0.31, p = 0.04; r = 0.40, p = 0.007; and r = -0.27, p = 0.07, respectively).

CONCLUSIONS

Impaired metabolic flexibility to fasting, reflected by an inability to transition away from carbohydrate oxidation, is linked with increased energy intake.

Breaking prolonged sitting increases 24-h physical activity and self-perceived energy levels but does not acutely affect cognition in healthy adults

INTRODUCTION

It is unknown whether predetermined (un)interrupted sitting within a laboratory setting will induce compensatory changes in human behaviours (energy intake and physical activity) once people return to a free-living environment. The effects of breaking up prolonged sitting on cognition are also unclear.

METHODS

Twenty-four (male = 13) healthy participants [age 31 ± 8 y, BMI 22.7 ± 2.3 kg/m2 (mean ± SD)] completed 320 min mixed-feeding trials under prolonged sitting (SIT) or with 2 min walking at 6.4 km/h every 20 min (ACTIVE), in a randomised crossover design. Human behaviours were recorded post-trial under free-living conditions until midnight. Cognitive performance was evaluated before and immediately after SIT and ACTIVE trials. Self-perceived sensations (appetite, energy and mood) and finger prick blood glucose levels were collected at regular intervals throughout the trials.

RESULTS

There were no differences between trials in eating behaviour and spontaneous physical activity (both, p > 0.05) in free-living conditions, resulting in greater overall total step counts [11,680 (10740,12620) versus 6049 (4845,7253) steps] and physical activity energy expenditure (PAEE) over 24-h period in ACTIVE compared to SIT (all, p < 0.05). Greater self-perceived levels of energy and lower blood glucose iAUC were found in ACTIVE trial compared to SIT trial (both, p < 0.05). No differences were found in cognitive performance between trials (all, p > 0.05).

CONCLUSION

Breaking up sitting does not elicit subsequent behavioural compensation, resulting in greater 24-h step counts and PAEE in healthy adults. Breaking up sitting reduces postprandial glucose concentrations and elicits greater self-perceived energy levels, but these positive effects do not acutely translate into improved cognitive function.

The impact of physical inactivity on glucose homeostasis when diet is adjusted to maintain energy balance in healthy, young males

BACKGROUND & AIMS

It is unclear if dietary adjustments to maintain energy balance during reduced physical activity can offset inactivity-induced reductions in insulin sensitivity and glucose disposal to produce normal daily glucose concentrations and meal responses. Therefore, the aim of the present study was to examine the impact of long-term physical inactivity (60 days of bed rest) on daily glycemia when in energy balance.

METHODS

Interstitial glucose concentrations were measured using Continuous Glucose Monitoring Systems (CGMS) for 5 days before and towards the end of bed rest in 20 healthy, young males (Age: 34 ± 8 years; BMI: 23.5 ± 1.8 kg/m2). Energy intake was reduced during bed rest to match energy expenditure, but the types of foods and timing of meals was maintained. Fasting venous glucose and insulin concentrations were determined, as well as the change in whole-body glucose disposal using a hyperinsulinemic-euglycemic clamp (HIEC).

RESULTS

Following long-term bed rest, fasting plasma insulin concentration increased 40% (p = 0.004) and glucose disposal during the HIEC decreased 24% (p < 0.001). Interstitial daily glucose total area under the curve (tAUC) from pre-to post-bed rest increased on average by 6% (p = 0.041), despite a 20 and 25% reduction in total caloric and carbohydrate intake, respectively. The nocturnal period (00:00-06:00) showed the greatest change to glycemia with glucose tAUC for this period increasing by 9% (p = 0.005). CGMS measures of daily glycemic variability (SD, J-Index, M-value and MAG) were not changed during bed rest.

CONCLUSIONS

Reduced physical activity (bed rest) increases glycemia even when daily energy intake is reduced to maintain energy balance. However, the disturbance to daily glucose homeostasis was much more modest than the reduced capacity to dispose of glucose, and glycemic variability was not negatively affected by bed rest, likely due to positive mitigating effects from the contemporaneous reduction in dietary energy and carbohydrate intake.

CLINICAL TRIALS RECORD

NCT03594799 (registered July 20, 2018) (https://clinicaltrials.gov/ct2/show/NCT03594799).

Associations between high-metabolic rate organ masses and fasting hunger: A study using whole-body magnetic resonance imaging in healthy males

BACKGROUND

Fat-free mass (FFM) has been shown to be positively associated with hunger and energy intake, an association mediated by resting metabolic rate (RMR). However, FFM comprises a heterogeneous group of tissues with distinct metabolic rates, and it remains unknown how specific high-metabolic rate organs contribute to the degree of perceived hunger.

OBJECTIVE

To examine whether FFM and its anatomical components were associated with fasting hunger when assessed at the tissue-organ level.

DESIGN

Body composition (quantitative magnetic resonance and magnetic resonance imaging), RMR and whole-body glucose oxidation (indirect calorimetry), HOMA-index as a marker of insulin sensitivity, nitrogen balance and fasting hunger (visual analogue scales) were assessed in 21 healthy males (age = 25 ± 3y; BMI = 23.4 ± 2.1 kg/m²) after 3 days of controlled energy balance.

RESULTS

FFM (r_s = 0.39; p = 0.09), RMR (r_s = 0.52; p = 0.02) and skeletal muscle mass (r_s = 0.57; p = 0.04), but not fat mass (r_s = -0.01; p = 0.99), were positively associated with fasting hunger. The association between the combined mass of high-metabolic rate organs (i.e., brain, liver, kidneys and heart; r_s = 0.58; p = 0.006) and fasting hunger was stronger than with FFM as a uniform body component. The strongest individual association was between liver mass and fasting hunger (r_s = 0.51; p = 0.02). No associations were observed between glucose parameters, markers of insulin sensitivity and fasting hunger. The encephalic measure, an index of brain-to-body energy allocation, was negatively associated with fasting hunger (r_s = -0.51; p = 0.02).

CONCLUSIONS

Fasting hunger was more strongly associated with the combined mass of high-metabolic rate organs than with FFM as a uniform body component, highlighting the importance of integrating individual tissue-organ masses and their functional correlates into homeostatic models of human appetite. The association between liver mass and fasting hunger may reflect its role in ensuring the brain's basal energy needs are met.

The acute effect of fasted exercise on energy intake, energy expenditure, subjective hunger and gastrointestinal hormone release compared to fed exercise in healthy individuals: a systematic review and network meta-analysis

OBJECTIVE

To determine the acute effect of fasted and fed exercise on energy intake, energy expenditure, subjective hunger and gastrointestinal hormone release.

METHODS

CENTRAL, Embase, MEDLINE, PsycInfo, PubMed, Scopus and Web of Science databases were searched to identify randomised, crossover studies in healthy individuals that compared the following interventions: (i) fasted exercise with a standardised post-exercise meal [FastEx + Meal], (ii) fasted exercise without a standardised post-exercise meal [FastEx + NoMeal], (iii) fed exercise with a standardised post-exercise meal [FedEx + Meal], (iv) fed exercise without a standardised post-exercise meal [FedEx + NoMeal]. Studies must have measured ad libitum meal energy intake, within-lab energy intake, 24-h energy intake, energy expenditure, subjective hunger, acyl-ghrelin, peptide YY, and/or glucagon-like peptide 1. Random-effect network meta-analyses were performed for outcomes containing ≥5 studies.

RESULTS

17 published articles (23 studies) were identified. Ad libitum meal energy intake was significantly lower during FedEx + Meal compared to FedEx + NoMeal (MD: -489 kJ; 95% CI, -898 to -80 kJ; P = 0.019). Within-lab energy intake was significantly lower during FastEx + NoMeal compared to FedEx + NoMeal (MD: -1326 kJ; 95% CI, -2102 to -550 kJ; P = 0.001). Similarly, 24-h energy intake following FastEx + NoMeal was significantly lower than FedEx + NoMeal (MD: -2095 kJ; 95% CI, -3910 kJ to -280 kJ; P = 0.024). Energy expenditure was however significantly lower during FastEx + NoMeal compared to FedEx+NoMeal (MD: -0.67 kJ/min; 95% CI, -1.10 to -0.23 kJ/min; P = 0.003). Subjective hunger was significantly higher during FastEx + Meal (MD: 13 mm; 95% CI, 5-21 mm; P = 0.001) and FastEx + NoMeal (MD: 23 mm; 95% CI, 16-30 mm; P < 0.001) compared to FedEx + NoMeal.

CONCLUSION

FastEx + NoMeal appears to be the most effective strategy to produce a short-term decrease in energy intake, but also results in increased hunger and lowered energy expenditure. Concerns regarding experimental design however lower the confidence in these findings, necessitating future research to rectify these issues when investigating exercise meal timing and energy balance.

PROSPERO REGISTRATION NUMBER

CRD42020208041.

KEY POINTS

Fed exercise with a standardised post-exercise meal resulted in the lowest energy intake at the ad libitum meal served following exercise completion. Fasted exercise without a standardised post-exercise meal resulted in the lowest within-lab and 24-h energy intake, but also produced the lowest energy expenditure and highest hunger. Methodological issues lower the confidence in these findings and necessitate future work to address identified problems.

The Impact of Long-term Physical Inactivity on Adipose Tissue Immunometabolism

CONTEXT

Adipose tissue and physical inactivity both influence metabolic health and systemic inflammation, but how adipose tissue responds to chronic physical inactivity is unknown.

OBJECTIVE

This work aimed to characterize the impact of chronic physical inactivity on adipose tissue in healthy, young males.

METHODS

We collected subcutaneous adipose tissue from 20 healthy, young men before and after 60 days of complete bed rest with energy intake reduced to maintain energy balance and fat mass. We used RNA sequencing, flow cytometry, ex vivo tissue culture, and targeted protein analyses to examine adipose tissue phenotype.

RESULTS

Our results indicate that the adipose tissue transcriptome, stromal cellular compartment, and insulin signaling protein abundance are largely unaffected by bed rest when fat mass is kept stable. However, there was an increase in the circulating concentration of several adipokines, including plasma leptin, which was associated with inactivity-induced increases in plasma insulin and absent from adipose tissue cultured ex vivo under standardized culture conditions.

CONCLUSION

Physical inactivity-induced disturbances to adipokine concentrations such as leptin, without changes to fat mass, could have profound metabolic implications outside a clinical facility when energy intake is not tightly controlled.

Physiological responses to carbohydrate overfeeding

PURPOSE OF REVIEW

To consider emerging research into the physiological effects of excessive dietary carbohydrate intake, with a particular focus on interactions with physical activity.

RECENT FINDINGS

A single episode of massive carbohydrate overload initiates physiological responses to stimulate additional peptide hormone secretion by the gut and the conversion of carbohydrate into lipid by the intestine, liver and adipose tissue. These acute responses maintain glycaemic control both via increased oxidation of carbohydrate (rather than lipid) and via nonoxidative disposal of surplus carbohydrate into endogenous glycogen and lipid storage depots. Sustained carbohydrate overfeeding therefore results in a chronic accumulation of lipid in the liver, skeletal muscle and adipose tissue, which can impair insulin sensitivity and cardiometabolic health in general. Beyond any direct effect of such lipid deposition on body mass/composition, there is not yet clear evidence of physiologically meaningful metabolic or behavioural adaptations to carbohydrate overfeeding in terms of other components of energy balance. However, regular physical exercise can mitigate the negative health effects of carbohydrate overfeeding, independent of any effect on the net carbohydrate surplus.

SUMMARY

Research in this area has advanced understanding regarding the mechanisms of weight gain and associated health outcomes within the modern context of an abundant supply of dietary carbohydrate.

Lactose-riched Mongolian mare's milk improves physical fatigue and exercise performance in mice

Fatigue may cause the efficiency of the organ in human body to decrease, which may affect the daily life and exercise performance of the general people and athletes. Mare's milk powder (MMP) is a lactose rich supplement. The research of the study is to evaluate the whether MMP has anti-fatigue effect. Forty male ICR mice were randomly divided into four group to receive vehicle or MMP by oral gavage at 0 (Vehicle), 0.27 (MMP-1X), 0.54 (MMP-2X), 1.35 (MMP-5X) g/kg/day for 14 days. The forelimb grip of the MMP-2X, and MMP-5X group were significantly higher than the vehicle group. The swim-to-exhaustion times of the MMP-1X, MMP-2X, and MMP-5X group were significantly greater than the vehicle group. Glycogen levels in liver and muscle were significantly larger in the MMP-1X, MMP-2X, and MMP-5X groups than the vehicle group. Receive MMP supplement for 14 days can promoting exercise performance and amelioration of exercise-induced fatigue.

Short-term interval exercise suppresses acylated ghrelin and hunger during caloric restriction in women with obesity

Caloric restriction is suggested to increase hunger, in part, through complex interactions of hormones and behavior that contribute to challenges in long-term weight loss. Although intense exercise may attenuate appetite, no data exist testing the effects of interval exercise (INT) during a low-calorie diet (LCD) on appetite regulation. We hypothesized that LCD+INT would favorably influence satiety when compared with an energy-deficit matched LCD in women with obesity. Twenty-six women with obesity (47.3±2.4 yrs; 37.3 ± 1.2 kg/m2) were randomized to either LCD (n = 13; mixed meals of ~1200 kcal/d) or LCD+INT (n = 13; 60 min/d of supervised interval exercise at 90% HRpeak for 3 min and 50% HRpeak for 3 min) for 2 weeks. An additional 350kcal (shake) was provided to LCD+INT individuals post-exercise to equate energy availability between groups. Total PYY, acylated ghrelin and des-ghrelin were measured at 0, 30 and 60 min of a 75g OGTT before and after the intervention. Visual analog scales were also administered at 0 and 120 min of the OGTT to assess appetite perception. Food logs were recorded prior to and during the intervention to ensure caloric intake compliance. Compared with pre-intervention conditions, both interventions decreased food intake (P = 0.001) and body fat (P < 0.01). There was no effect on fasting PYY, but both LCD and LCD+INT increased post-prandial PYY iAUC (P < 0.001) relative to pre-intervention. LCD+INT maintained fasting acylated ghrelin (P = 0.06) and suppressed post-prandial acylated ghrelin iAUC (P = 0.04) compared to LCD. Neither intervention impacted circulating des- ghrelin before or following the OGTT. Interestingly, LCD+INT attenuated fasting hunger and maintained fullness compared with LCD (P = 0.05 and P = 0.06, respectively). Taken together, interval exercise favors acylated ghrelin suppression and perception of hunger during a LCD in women with obesity.

Intermittent versus continuous enteral nutrition attenuates increases in insulin and leptin during short-term bed rest

PURPOSE

To compare endocrine responses to intermittent vs continuous enteral nutrition provision during short-term bed rest.

METHODS

Twenty healthy men underwent 7 days of bed rest, during which they were randomized to receive enteral nutrition (47%E as carbohydrate, 34%E as fat, 16%E as protein and 3%E as fibre) in a continuous (CONTINUOUS; n = 10; 24 h day-1 at a constant rate) or intermittent (INTERMITTENT; n = 10; as 4 meals per day separated by 5 h) pattern. Daily plasma samples were taken every morning to assess metabolite/hormone concentrations.

RESULTS

During bed rest, plasma leptin concentrations were elevated to a lesser extent with INTERMITTENT vs CONTINUOUS (iAUC: 0.42 ± 0.38 vs 0.95 ± 0.48 nmol L-1, respectively; P = 0.014) as were insulin concentrations (interaction effect, P < 0.001) which reached a peak of 369 ± 225 pmol L-1 in CONTINUOUS, compared to 94 ± 38 pmol L-1 in INTERMITTENT (P = 0.001). Changes in glucose infusion rate were positively correlated with changes in fasting plasma GLP-1 concentrations (r = 0.44, P = 0.049).

CONCLUSION

Intermittent enteral nutrition attenuates the progressive rise in plasma leptin and insulinemia seen with continuous feeding during bed rest, suggesting that continuous feeding increases insulin requirements to maintain euglycemia. This raises the possibility that hepatic insulin sensitivity is impaired to a greater extent with continuous versus intermittent feeding during bed rest. To attenuate endocrine and metabolic changes with enteral feeding, an intermittent feeding strategy may, therefore, be preferable to continuous provision of nutrition. This trial was registered on clinicaltrials.gov as NCT02521025.

Appetite and energy intake responses to breakfast consumption and carbohydrate supplementation in hypoxia

PURPOSE

The purpose of experiment one was to determine the appetite, acylated ghrelin and energy intake response to breakfast consumption and omission in hypoxia and normoxia. Experiment two aimed to determine the appetite, acylated ghrelin and energy intake response to carbohydrate supplementation after both breakfast consumption and omission in hypoxia.

METHODS

In experiment one, twelve participants rested and exercised once after breakfast consumption and once after omission in normobaric hypoxia (4300 m: F_iO₂ ~11.7%) and normoxia. In experiment two, eleven participants rested and exercised in normobaric hypoxia (4300 m: F_iO₂ ~11.7%), twice after consuming a high carbohydrate breakfast and twice after breakfast omission. Participants consumed both a carbohydrate (1.2g·min^-1 glucose) and a placebo beverage after breakfast consumption and omission. Measures of appetite perceptions and acylated ghrelin were taken at regular intervals throughout both experiments and an ad-libitum meal was provided post-exercise to quantify energy intake.

RESULTS

Breakfast consumption had no significant effect on post exercise energy intake or acylated ghrelin concentrations, despite reductions in appetite perceptions. As such, breakfast consumption increased total trial energy intake compared with breakfast omission in hypoxia (7136 ± 2047 kJ vs. 5412 ± 1652 kJ; p = 0.02) and normoxia (9276 ± 3058 vs. 6654 ± 2091 kJ; p < 0.01). Carbohydrate supplementation had no effect on appetite perceptions or acylated ghrelin concentrations after breakfast consumption or omission. As such, carbohydrate supplementation increased total energy intake after breakfast consumption (10222 ± 2831 kJ vs. 7695 ± 1970 kJ p < 0.01) and omission (8058 ± 2574 kJ vs. 6174 ± 2222 kJ p = 0.02).

CONCLUSION

Both breakfast consumption and carbohydrate supplementation provide beneficial dietary interventions for increasing energy intake in hypoxic conditions.

Effects of a four-week very low-carbohydrate high-fat diet on biomarkers of inflammation: Non-randomised parallel-group study

BACKGROUND

It is commonly assumed that increased dietary fat and/or caloric excess induces chronic inflammatory processes, since the association between obesity and chronic adipose tissue with systemic inflammation has been shown previously. As far as we know, the reported health benefits of a VLCHF or ketogenic diet have not adequately involved an evaluation of biomarkers of inflammation.

AIM

This study investigated the effects of a four-week very low-carbohydrate high-fat (VLCHF) diet in healthy young individuals on biomarkers of inflammation.

METHODS

Eighteen moderately trained males (age 23.8 ± 2.1 years) were assigned to two groups. One group switched to a non-standardised VLCHF diet for four weeks, while the second group remained consuming their normal habitual diet (HD). Biomarkers of inflammation (adiponectin, leptin, resistin and interleukin-6) and substrate metabolism (fasting glucose and triacylglyceride concentrations) were analysed from blood at baseline and after four weeks.

RESULTS

There was moderate evidence for substantial changes in leptin serum concentrations in the VLCHF group, with small to large decreases compared to the HD group after four weeks (effect size = 0.78, 95% CI 0.42, 0.93, p = 0.008; Bayes Factor₁₀ = 5.70). No substantial between-group change differences over time were found across any other biomarkers.

CONCLUSIONS

A four-week period of consuming a VLCHF diet in healthy young men was not associated with any considerable changes in markers of inflammation but showed evidence for lowered serum leptin concentrations relative to the HD group.

Post-exercise carbohydrate and energy availability induce independent effects on skeletal muscle cell signalling and bone turnover: implications for training adaptation

KEY POINTS

Reduced carbohydrate (CHO) availability before and after exercise may augment endurance training-induced adaptations of human skeletal muscle, as mediated via modulation of cell signalling pathways. However, it is not known whether such responses are mediated by CHO restriction, energy restriction or a combination of both. In recovery from a twice per day training protocol where muscle glycogen concentration is maintained within 200-350 mmol kg^-1 dry weight (dw), we demonstrate that acute post-exercise CHO and energy restriction (i.e. < 24 h) does not potentiate potent cell signalling pathways that regulate hallmark adaptations associated with endurance training. In contrast, consuming CHO before, during and after an acute training session attenuated markers of bone resorption, effects that are independent of energy availability. Whilst the enhanced muscle adaptations associated with CHO restriction may be regulated by absolute muscle glycogen concentration, the acute within-day fluctuations in CHO availability inherent to twice per day training may have chronic implications for bone turnover.

ABSTRACT

We examined the effects of post-exercise carbohydrate (CHO) and energy availability (EA) on potent skeletal muscle cell signalling pathways (regulating mitochondrial biogenesis and lipid metabolism) and indicators of bone metabolism. In a repeated measures design, nine males completed a morning (AM) and afternoon (PM) high-intensity interval (HIT) (8 × 5 min at 85% V ̇ O 2 peak ) running protocol (interspersed by 3.5 h) under dietary conditions of (1) high CHO availability (HCHO: CHO ∼12 g kg^-1 , EA∼ 60 kcal kg^-1 fat free mass (FFM)), (2) reduced CHO but high fat availability (LCHF: CHO ∼3 (^-1 , EA∼ 60 kcal kg^-1 FFM) or (3), reduced CHO and reduced energy availability (LCAL: CHO ∼3 g kg^-1 , EA∼ 20 kcal kg^-1 FFM). Muscle glycogen was reduced to ∼200 mmol kg^-1  dw in all trials immediately post PM HIT (P < 0.01) and remained lower at 17 h (171, 194 and 316 mmol kg^-1  dw) post PM HIT in LCHF and LCAL (P < 0.001) compared to HCHO. Exercise induced comparable p38MAPK phosphorylation (P < 0.05) immediately post PM HIT and similar mRNA expression (all P < 0.05) of PGC-1α, p53 and CPT1 mRNA in HCHO, LCHF and LCAL. Post-exercise circulating βCTX was lower in HCHO (P < 0.05) compared to LCHF and LCAL whereas exercise-induced increases in IL-6 were larger in LCAL (P < 0.05) compared to LCHF and HCHO. In conditions where glycogen concentration is maintained within 200-350 mmol kg^-1  dw, we conclude post-exercise CHO and energy restriction (i.e. < 24 h) does not potentiate cell signalling pathways that regulate hallmark adaptations associated with endurance training. In contrast, consuming CHO before, during and after HIT running attenuates bone resorption, effects that are independent of energy availability and circulating IL-6.