Characterising 24-h skeletal muscle gene expression alongside metabolic & endocrine responses under diurnal conditions.

CONTEXT: Skeletal muscle plays a central role in the storage, synthesis, and breakdown of nutrients, yet little research has explored temporal responses of this human tissue, especially with concurrent measures of systemic biomarkers of metabolism. OBJECTIVE: To characterise temporal profiles in skeletal muscle expression of genes involved in carbohydrate metabolism, lipid metabolism, circadian clocks, and autophagy and descriptively relate them to systemic metabolites and hormones during a controlled laboratory protocol. METHODS: Ten healthy adults (9M/1F, mean ± SD: age: 30 ± 10 y; BMI: 24.1 ± 2.7 kg·m-2) rested in the laboratory for 37 hours with all data collected during the final 24 hours of this period (i.e., 0800-0800 h). Participants ingested hourly isocaloric liquid meal replacements alongside appetite assessments during waking before a sleep opportunity from 2200-0700 h. Blood samples were collected hourly for endocrine and metabolite analyses, with muscle biopsies occurring every 4 h from 1200 h to 0800 h the following day to quantify gene expression. RESULTS: Plasma insulin displayed diurnal rhythmicity peaking at 1804 h. Expression of skeletal muscle genes involved in carbohydrate metabolism (Name - Acrophase; GLUT4 - 1440 h; PPARGC1A -1613 h; HK2 - 1824 h) and lipid metabolism (FABP3 - 1237 h; PDK4 - 0530 h; CPT1B - 1258 h) displayed 24 h rhythmicity that reflected the temporal rhythm of insulin. Equally, circulating glucose (0019 h), NEFA (0456 h), glycerol (0432 h), triglyceride (2314 h), urea (0046 h), CTX (0507 h) and cortisol concentrations (2250 h) also all displayed diurnal rhythmicity. CONCLUSION: Diurnal rhythms were present in human skeletal muscle gene expression as well systemic metabolites and hormones under controlled diurnal conditions. The temporal patterns of genes relating to carbohydrate and lipid metabolism alongside circulating insulin are consistent with diurnal rhythms being driven in part by the diurnal influence of cyclic feeding and fasting.

Effects of dietary inorganic nitrate on blood pressure during and post-exercise recovery: A systematic review and meta-analysis of randomized placebo-controlled trials.

OBJECTIVES: A systematic review with meta-analysis was completed to study the effects of dietary inorganic nitrate (NO3-) oral ingestion from vegetables and salts on blood pressure responses during and following exercise. BACKGROUND: NO3- is a hypotensive agent with the potential to reduce blood pressure peaks during exercise and amplify exercise-induced hypotensive effects. Several randomized and controlled trials have investigated the effects of NO3- on hemodynamic responses to physical exercise, however this still has yet to be studied systematically. METHODS: The searches were conducted on EMBASE, Medline, and SPORTSDiscus databases. The study included masked randomized controlled trials (RCTs) with participants ≥18 years old. The NO3-intervention group received at least 50 mg NO3-/day with similar sources amid NO3- and placebo conditions. Included studies reported systolic blood pressure (SBP) or diastolic blood pressure (DBP) values during or following exercise performance. RESULTS: 1903 studies were identified, and twenty-six achieved the inclusion criteria. NO3- daily dosages ranged from 90 to 800 mg/day. Throughout exercise, SBP had smaller increases in the NO3- group (-2.81 mmHg (95%CI: -5.20 to -0.41), p=0.02. DBP demonstrated lower values in the NO3- group (-2.41 mmHg (95%CI: -4.02 to -0.79), p=0.003. In the post-exercise group, the NO3- group presented lower SBP values (-3.53 mmHg (95%CI: -5.65 to 1.41), p=0.001, while no changes were identified in DBP values between NO3- and placebo groups (p=0.31). Subgroup meta-analysis revealed that SBP baseline values, exercise type, duration of NO3- ingestion, and its dosages mediated blood pressure responses during and following exercise. CONCLUSIONS: NO3- ingestion prior to exercise attenuated the increases in SBP and DBP during exercise, and increased the decline in SBP after exercise. These results are dependent on factors that moderate the blood pressure responses (e.g., health status, type of exercise, resting blood pressure values).

Whey Protein-Enriched and Carbohydrate-Rich Breakfasts Attenuate Insulinemic Responses to an ad libitum Lunch Relative to Extended Morning Fasting: A Randomized Crossover Trial.

BACKGROUND: Typical breakfast foods are rich in carbohydrate, so they not only elevate blood glucose during the morning, but also elicit a second-meal effect that can attenuate blood glucose responses in the afternoon. OBJECTIVES: To determine whether a reduced-carbohydrate protein-enriched breakfast can elicit similar effects on glucose control later in the day but without hyperglycemia in the morning. METHODS: In a randomized crossover design, 12 healthy men and women (age 22 ± 2 y, BMI 24.1 ± 3.6 kg·m-2; Mean ± SD) completed 3 experimental conditions. In all conditions, participants consumed an ad libitum lunch at 1200 ± 1 h but differed in terms of whether they had fasted all morning (control) or had consumed a standardized porridge breakfast at 0900 ± 1 h (320 ± 50 kcal; prescribed relative to resting metabolic rate) that was either carbohydrate-rich (50 ± 10 g CHO) or protein-enriched (that is, isoenergetic substitution of carbohydrate for 15 g whey protein isolate). RESULTS: The protein-enriched breakfast reduced the morning glycemic response (iAUC 87 ± 36 mmol·L-1·180 min) relative to the carbohydrate-rich breakfast (119 ± 37 mmol·L-1·180 min; P = 0.03). Despite similar energy intake at lunch in all 3 conditions (protein-enriched 769 ± 278 kcal; carbohydrate-rich 753 ± 223 kcal; fasting 790 ± 227 kcal), postlunch insulinemic responses were markedly attenuated when breakfasts had been consumed that were either protein-enriched (18.0 ± 8.0 nmol·L-1·120 min; P = 0.05) or carbohydrate-rich (16.0 ± 7.7 nmol·L-1·120 min; P = 0.005), relative to when lunch was consumed in an overnight fasted state (26.9 ± 13.5 nmol·L-1·120 min). CONCLUSIONS: Breakfast consumption attenuates insulinemic responses to a subsequent meal, achieved with consumption of energy-matched breakfasts typically high in carbohydrates or enriched with whey protein isolate relative to extended morning fasting. TRIAL REGISTRATION NUMBER: NCT03866720 (clinicaltrials.gov).

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).

Understanding the role of physical activity on the pathway from intra-articular knee injury to post-traumatic osteoarthritis disease in young people: a scoping review protocol.

INTRODUCTION: The prevalence of intra-articular knee injuries and reparative surgeries is increasing in many countries. Alarmingly, there is a risk of developing post-traumatic osteoarthritis (PTOA) after sustaining a serious intra-articular knee injury. Although physical inactivity is suggested as a risk factor contributing to the high prevalence of the condition, there is a paucity of research characterising the association between physical activity and joint health. Consequently, the primary aim of this review will be to identify and present available empirical evidence regarding the association between physical activity and joint degeneration after intra-articular knee injury and summarise the evidence using an adapted Grading of Recommendations Assessment, Development and Evaluations. The secondary aim will be to identify potential mechanistic pathways through which physical activity could influence PTOA pathogenesis. The tertiary aim will be to highlight gaps in current understanding of the association between physical activity and joint degeneration following joint injury. METHODS: A scoping review will be conducted using the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews checklist and best-practice recommendations. The review will be guided by the following research question: what is the role of physical activity in the trajectory from intra-articular knee injury to PTOA in young men and women? We will identify primary research studies and grey literature by searching the electronic databases Scopus, Embase: Elsevier, PubMed, Web of Science: all databases, and Google Scholar. Reviewing pairs will screen abstracts, full texts and will extract data. Data will be presented descriptively using charts, graphs, plots and tables. ETHICS AND DISSEMINATION: This research does not require ethical approval due to the data being published and publicly available. This review will be submitted for publication in a peer-reviewed sports medicine journal irrespective of discoveries and disseminated through scientific conference presentations and social media. TRIAL REGISTRATION NUMBER: https://osf.io/84pnh/.

Ketone monoester ingestion increases postexercise serum erythropoietin concentrations in healthy men.

Intravenous ketone body infusion can increase erythropoietin (EPO) concentrations, but responses to ketone monoester ingestion postexercise are currently unknown. The purpose of this study was to assess the effect of ketone monoester ingestion on postexercise erythropoietin (EPO) concentrations. Nine healthy men completed two trials in a randomized, crossover design (1-wk washout). During trials, participants performed 1 h of cycling (initially alternating between 50% and 90% of maximal aerobic capacity for 2 min each interval, and then 50% and 80%, and 50% and 70% when the higher intensity was unsustainable). Participants ingested 0.8 g·kg-1 sucrose with 0.4 g·kg-1 protein immediately after exercise, and at 1, 2, and 3 h postexercise. During the control trial (CONTROL), no further nutrition was provided, whereas on the ketone monoester trial (KETONE), participants also ingested 0.29 g·kg-1 of the ketone monoester (R)-3-hydroxybutyl (R)-3-hydroxybutyrate immediately postexercise and at 1 and 2 h postexercise. Blood was sampled immediately postexercise, every 15 min in the first hour and hourly thereafter for 4 h. Serum EPO concentrations increased to a greater extent in KETONE than in CONTROL (time × condition interaction: P = 0.046). Peak serum EPO concentrations were higher with KETONE (means ± SD: 9.0 ± 2.3 IU·L-1) compared with CONTROL (7.5 ± 1.5 IU·L-1, P < 0.01). Serum ß-hydroxybutyrate concentrations were also higher, and glucose concentrations lower, with KETONE versus CONTROL (both P < 0.01). In conclusion, ketone monoester ingestion increases postexercise erythropoietin concentrations, revealing a new avenue for orally ingestible ketone monoesters to potentially alter hemoglobin mass.NEW & NOTEWORTHY To our knowledge, this study was the first to assess the effects of ketone monoester ingestion on erythropoietin concentrations after exercise. We demonstrated that ingestion of a ketone monoester postexercise increased serum erythropoietin concentrations and reduced serum glucose concentrations in healthy men. These data reveal the possibility for ketone monoesters to alter hemoglobin mass.

Restricting sugar or carbohydrate intake does not impact physical activity level or energy intake over 24 h despite changes in substrate use: a randomised crossover study in healthy men and women.

PURPOSE: To determine the effects of dietary sugar or carbohydrate restriction on physical activity energy expenditure, energy intake, and physiological outcomes across 24 h. METHODS: In a randomized, open-label crossover design, twenty-five healthy men (n = 10) and women (n = 15) consumed three diets over a 24-h period: moderate carbohydrate and sugar content (MODSUG = 50% carbohydrate [20% sugars], 15% protein, 35% fat); low sugar content (LOWSUG = 50% carbohydrate [< 5% sugars], 15% protein, 35% fat); and low carbohydrate content (LOWCHO = 8% carbohydrate [< 5% sugars], 15% protein, 77% fat). Postprandial metabolic responses to a prescribed breakfast (20% EI) were monitored under laboratory conditions before an ad libitum test lunch, with subsequent diet and physical activity monitoring under free-living conditions until blood sample collection the following morning. RESULTS: The MODSUG, LOWSUG and LOWCHO diets resulted in similar mean [95%CI] rates of both physical activity energy expenditure (771 [624, 919] vs. 677 [565, 789] vs. 802 [614, 991] kcal·d-1; p = 0.29] and energy intake (2071 [1794, 2347] vs. 2195 [1918, 2473] vs. 2194 [1890, 2498] kcal·d-1; P = 0.34), respectively. The LOWCHO condition elicited the lowest glycaemic and insulinaemic responses to breakfast (P < 0.01) but the highest 24-h increase in LDL-cholesterol concentrations (P < 0.001), with no differences between the MODSUG and LOWSUG treatments. Leptin concentrations decreased over 24-h of consuming LOWCHO relative to LOWSUG (p < 0.01). CONCLUSION: When energy density is controlled for, restricting either sugar or total dietary carbohydrate does not modulate physical activity level or energy intake over a 24-h period (~ 19-h free-living) despite substantial metabolic changes. CLINICAL TRIALS REGISTRATION ID: NCT03509610, https://clinicaltrials.gov/show/NCT03509610.

Interrupting Prolonged Sitting with Intermittent Walking Increases Postprandial Gut Hormone Responses.

INTRODUCTION: Continuous exercise can increase postprandial gut hormone such as glucagon-like peptide 1 (GLP-1) and peptide YY (PYY) responses, but it is unknown whether interrupting prolonged sitting with intermittent walking elicits this effect. METHOD: Ten participants with central overweight/obesity (7 men and 3 postmenopausal women, 51 ± 5 yr; mean ± SD) completed a randomized crossover study in which they consumed breakfast and lunch in the laboratory while either sitting continuously for the entire 5.5-h period (SIT) or the prolonged sitting interrupted every 20 min by walking briskly (6.4 km·h-1) for 2 min (BREAKS). Blood samples were collected at regular intervals to examine postprandial plasma GLP-1, PYY, and glucose-dependent insulinotropic polypeptide concentrations. Adipose tissue samples were collected at baseline and at the end of the trials to examine changes in net dipeptidyl peptidase 4 secretion from primary explants. RESULTS: Mean (95% confidence interval) postprandial GLP-1 and PYY incremental area under curve values were elevated by 26% and 31% in the BREAKS trial versus SIT (8.4 [0.7, 16.1] vs 6.7 [-0.8, 14.2], P = 0.001, and 26.9 [8.1, 45.6] vs 20.4 [5.1, 35.8] nmol·330 min·L-1, P = 0.024, respectively) but without any such effect on glucose-dependent insulinotropic polypeptide (P = 0.076) or net adipose tissue dipeptidyl peptidase 4 secretion (P > 0.05). CONCLUSIONS: Interrupting prolonged sitting with regular short bouts of brisk walking increases postprandial GLP-1 and PYY concentrations in healthy middle-age men and women with central adiposity.

Divergent immunometabolic changes in adipose tissue and skeletal muscle with ageing in healthy humans.

KEY POINTS: Ageing is associated with increased systemic inflammation and metabolic dysfunction that contributes to the development of age-associated diseases. The role of adipose tissue in immunometabolic alterations that take place with ageing is unknown in humans. We show, in healthy, active and lean older adults, that adipose tissue, but not skeletal muscle, displays considerable pro-inflammatory transcriptomic, cellular and secretory changes, as well as a reduction in insulin signalling proteins compared to younger adults. These findings indicate that adipose tissue undergoes substantial immunometabolic alterations with ageing, and that these changes are tissue-specific and more profound than those observed in skeletal muscle or in the circulation. These results identify adipose tissue as an important tissue in the biological ageing process in humans, which may exhibit signs of immunometabolic dysfunction prior to systemic manifestation. ABSTRACT: Ageing and obesity are both characterized by inflammation and a deterioration in metabolic health. It is now clear that adipose tissue plays a major role in inflammation and metabolic control in obesity, although little is known about the role of adipose tissue in human ageing. To understand how ageing impacts adipose tissue, we characterized subcutaneous adipose tissue and skeletal muscle samples from twelve younger (27 ± 4 years [Young]) and twelve older (66 ± 5 years [Old]) active/non-obese males. We performed a wide-range of whole-body and tissue measures, including RNA-sequencing and multicolour flow cytometry. We also measured a range of inflammatory and metabolic proteins in the circulation and their release by adipose tissue, ex vivo. Both adipose tissue and muscle had ∼2-fold more immune cells per gram of tissue with ageing. In adipose tissue, this immune cell infiltration was driven by increased memory/effector T-cells, whereas, in muscle, the accumulation was driven by memory/effector T-cells and macrophages. Transcriptomic analysis revealed that, with ageing, adipose tissue, but not muscle, was enriched for inflammatory transcripts/pathways related to acquired and innate immunity. Ageing also increased the adipose tissue pro-inflammatory secretory profile. Insulin signalling protein content was reduced in adipose tissue, but not muscle. Our findings indicate that adipose tissue undergoes substantial immunometabolic changes with ageing in humans, and that these changes are tissue-specific and more profound than those observed in the circulation and skeletal muscle.

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.

A randomized controlled trial to isolate the effects of fasting and energy restriction on weight loss and metabolic health in lean adults.

Intermittent fasting may impart metabolic benefits independent of energy balance by initiating fasting-mediated mechanisms. This randomized controlled trial examined 24-hour fasting with 150% energy intake on alternate days for 3 weeks in lean, healthy individuals (0:150; n = 12). Control groups involved a matched degree of energy restriction applied continuously without fasting (75% energy intake daily; 75:75; n = 12) or a matched pattern of fasting without net energy restriction (200% energy intake on alternate days; 0:200; n = 12). Primary outcomes were body composition, components of energy balance, and postprandial metabolism. Daily energy restriction (75:75) reduced body mass (-1.91 ± 0.99 kilograms) almost entirely due to fat loss (-1.75 ± 0.79 kilograms). Restricting energy intake via fasting (0:150) also decreased body mass (-1.60 ± 1.06 kilograms; P = 0.46 versus 75:75) but with attenuated reductions in body fat (-0.74 ± 1.32 kilograms; P = 0.01 versus 75:75), whereas fasting without energy restriction (0:200) did not significantly reduce either body mass (-0.52 ± 1.09 kilograms; P ≤ 0.04 versus 75:75 and 0:150) or fat mass (-0.12 ± 0.68 kilograms; P ≤ 0.05 versus 75:75 and 0:150). Postprandial indices of cardiometabolic health and gut hormones, along with the expression of key genes in subcutaneous adipose tissue, were not statistically different between groups (P > 0.05). Alternate-day fasting less effectively reduces body fat mass than a matched degree of daily energy restriction and without evidence of fasting-specific effects on metabolic regulation or cardiovascular health.

Interactive effects of acute exercise and carbohydrate-energy replacement on insulin sensitivity in healthy adults.

This study investigated whether carbohydrate-energy replacement immediately after prolonged endurance exercise attenuates insulin sensitivity the following morning, and whether exercise improves insulin sensitivity the following morning independent of an exercise-induced carbohydrate deficit. Oral glucose tolerance and whole-body insulin sensitivity were compared the morning after 3 evening conditions, involving (1) treadmill exercise followed by a carbohydrate replacement drink (200 or 150 g maltodextrin for males and females, respectively; CHO-replace); (2) treadmill exercise followed by a non-caloric, taste-matched placebo (CHO-deficit); or (3) seated rest with no drink provided (Rest). Treadmill exercise involved 90 minutes at ∼80% age-predicted maximum heart rate. Seven males and 2 females (aged 23 ± 1 years; body mass index 24.0 ± 2.7 kg·m-2) completed all conditions in a randomised order. Matsuda index improved by 22% (2.2 [0.3, 4.0] au, p = 0.03) and HOMA2-IR improved by 10% (-0.04 [-0.08, 0.00] au, p = 0.04) in CHO-deficit versus CHO-replace, without corresponding changes in postprandial glycaemia. Outcomes were similar between Rest and other conditions. These data suggest that improvements to insulin sensitivity in healthy populations following acute moderate/vigorous intensity endurance exercise may be dependent on the presence of a carbohydrate-energy deficit. Novelty: Restoration of carbohydrate balance following acute endurance exercise attenuated whole-body insulin sensitivity. Exercise per se failed to enhance whole-body insulin sensitivity. Maximising or prolonging the post-exercise carbohydrate deficit may enhance acute benefits to insulin sensitivity.

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.

Unacylated ghrelin, leptin, and appetite display diurnal rhythmicity in lean adults.

Constant routine and forced desynchrony protocols typically remove the effects of behavioral/environmental cues to examine endogenous circadian rhythms, yet this may not reflect rhythms of appetite regulation in the real world. It is therefore important to understand these rhythms within the same subjects under controlled diurnal conditions of light, sleep, and feeding. Ten healthy adults (9 M/1 F, means ±SD: age, 30 ± 10 yr; body mass index, 24.1 ± 2.7 kg·m-2) rested supine in the laboratory for 37 h. All data were collected during the final 24 h of this period (i.e., 0800-0800 h). Participants were fed hourly isocaloric liquid meal replacements alongside appetite assessments during waking before a sleep opportunity from 2200 to 0700 h. Hourly blood samples were collected throughout the 24-h period. Dim light melatonin onset occurred at 2318 ± 46 min. A diurnal rhythm in mean plasma unacylated ghrelin concentration was identified (P = 0.04), with the acrophase occurring shortly after waking (0819), falling to a nadir in the evening with a relative amplitude of 9%. Plasma leptin concentration also exhibited a diurnal rhythm (P < 0.01), with the acrophase occurring shortly after lights-out (0032 h) and the lowest concentrations at midday. The amplitude for this rhythm was 25%. Diurnal rhythms were established in all dimensions of appetite except for sweet preference (P = 0.29), with both hunger (2103 h) and prospective food consumption (1955 h) reaching their peak in the evening before falling to their nadir shortly after waking. Under controlled diurnal conditions, simultaneous measurement of leptin, unacylated ghrelin, and subjective appetite over a 24-h period revealed rhythmicity in appetite regulation in lean, healthy humans.NEW & NOTEWORTHY Simultaneous assessment of subjective appetite, unacylated ghrelin, and leptin was carried out over a continuous 37-h protocol for the first time under conditions of controlled light, sleep, and feeding in healthy, lean adults. Rhythms were observed in unacylated ghrelin, leptin, and components of subjective appetite, such as hunger, prospective consumption, and fullness. Concurrent measurement of rhythms in these variables is important to fully understand the temporal relationships between components of appetite as well as the influence of diurnal factors such as sleep, light, and feeding.

Resting skeletal muscle PNPLA2 (ATGL) and CPT1B are associated with peak fat oxidation rates in men and women but do not explain observed sex differences.

NEW FINDINGS: What is the central question of this study? What is the relationship between proteins in skeletal muscle and adipose tissue determined at rest and at peak rates of fat oxidation in men and women? What is the main finding and its importance? The resting contents of proteins in skeletal muscle involved in triglyceride hydrolysis and mitochondrial lipid transport were more strongly associated with peak fat oxidation rates than proteins related to lipid transport or hydrolysis in adipose tissue. Although females displayed higher relative rates of fat oxidation than males, this was not explained by the proteins measured in this study, suggesting that other factors determine sex differences in fat metabolism. ABSTRACT: We explored key proteins involved in fat metabolism that might be associated with peak fat oxidation (PFO) and account for sexual dimorphism in fuel metabolism during exercise. Thirty-six healthy adults [15 women; 40 ± 11 years of age; peak oxygen consumption 42.5 ± 9.5 ml (kg body mass)-1  min-1 ; mean ± SD] completed two exercise tests to determine PFO via indirect calorimetry. Resting adipose tissue and/or skeletal muscle biopsies were obtained to determine the adipose tissue protein content of PLIN1, ABHD5 (CGI-58), LIPE (HSL), PNPLA2 (ATGL), ACSL1, CPT1B and oestrogen receptor α (ERα) and the skeletal muscle protein content of FABP 3 (FABPpm), PNPLA2 (ATGL), ACSL1, CTP1B and ESR1 (ERα). Moderate strength correlations were found between PFO [in milligrams per kilogram of fat-free mass (FFM) per minute] and the protein content of PNPLA2 (ATGL) [rs  = 0.41 (0.03-0.68), P < 0.05] and CPT1B [rs  = 0.45 (0.09-0.71), P < 0.05] in skeletal muscle. No other statistically significant bivariate correlations were found consistently. Females had a greater relative PFO than males [7.1 ± 1.9 vs. 4.5 ± 1.3 and 7.3 ± 1.7 vs. 4.8 ± 1.2 mg (kg FFM)-1  min-1 in the adipose tissue (n = 14) and skeletal muscle (n = 12) subgroups, respectively (P < 0.05)]. No statistically significant sex differences were found in the content of these proteins. The regulation of PFO might involve processes relating to intramyocellular triglyceride hydrolysis and mitochondrial fatty acid transport, and adipose tissue is likely to play a more minor role than muscle. Sex differences in fat metabolism are likely to be attributable to factors other than the resting content of proteins in skeletal muscle and adipose tissue relating to triglyceride hydrolysis and fatty acid transport.

Muscle Glycogen Utilization during Exercise after Ingestion of Alcohol.

PURPOSE: Ingested ethanol (EtOH) is metabolized gastrically and hepatically, which may influence resting and exercise metabolism. Previous exercise studies have provided EtOH intravenously rather than orally, altering the metabolic effects of EtOH. No studies to date have investigated the effects of EtOH ingestion on systemic and peripheral (e.g., skeletal muscle) exercise metabolism. METHODS: Eight men (mean ± SD; age = 24 ± 5 yr, body mass = 76.7 ± 5.6 kg, height = 1.80 ± 0.04 m, V˙O2peak = 4.1 ± 0.2 L·min) performed two bouts of fasted cycling exercise at 55% V˙O2peak for 2 h, with (EtOH) and without (control) prior ingestion of EtOH 1 h and immediately before exercise (total dose = 0.1 g·kg lean body mass·h; 30.2 ± 1.1 g 40% ABV Vodka; fed in two equal boluses) in a randomized order, separated by 7-10 d. RESULTS: Muscle glycogen use during exercise was not different between conditions (mean [normalized 95% confidence interval]; EtOH, 229 [156-302] mmol·kg dm, vs control, 258 [185-331] mmol·kg dm; P = 0.67). Mean plasma glucose concentrations during exercise were similar (control, 5.26 [5.22-5.30], vs EtOH, 5.34 [5.30-5.38]; P = 0.06). EtOH ingestion resulted in similar plasma nonesterified fatty acid concentrations compared with rest (control, 0.43 [0.31-0.55] mmol·L, vs EtOH, 0.30 [0.21-0.40] mmol·L) and during exercise. Plasma lactate concentration was higher during the first 30 min of rest after EtOH consumption (mean concentration; control, 0.83 [0.77-0.90] mmol·L, vs EtOH, 1.00 [0.93-1.07] mmol·L), but the response during exercise was similar between conditions. CONCLUSIONS: Muscle glycogen utilization was similar during exercise with or without prior EtOH ingestion, reflected in similar total whole-body carbohydrate oxidation rates observed.

Glucose control upon waking is unaffected by hourly sleep fragmentation during the night, but is impaired by morning caffeinated coffee.

Morning coffee is a common remedy following disrupted sleep, yet each factor can independently impair glucose tolerance and insulin sensitivity in healthy adults. Remarkably, the combined effects of sleep fragmentation and coffee on glucose control upon waking per se have never been investigated. In a randomised crossover design, twenty-nine adults (mean age: 21 (sd 1) years, BMI: 24·4 (sd 3·3) kg/m2) underwent three oral glucose tolerance tests (OGTT). One following a habitual night of sleep (Control; in bed, lights-off trying to sleep approximately 23.00-07.00 hours), the others following a night of sleep fragmentation (as Control but waking hourly for 5 min), with and without morning coffee approximately 1 h after waking (approximately 300 mg caffeine as black coffee 30 min prior to OGTT). Individualised peak plasma glucose and insulin concentrations were unaffected by sleep quality but were higher following coffee consumption (mean (normalised CI) for Control, Fragmented and Fragmented + Coffee, respectively; glucose: 8·20 (normalised CI 7·93, 8·47) mmol/l v. 8·23 (normalised CI 7·96, 8·50) mmol/l v. 8·96 (normalised CI 8·70, 9·22) mmol/l; insulin: 265 (normalised CI 247, 283) pmol/l; and 235 (normalised CI 218, 253) pmol/l; and 310 (normalised CI 284, 337) pmol/l). Likewise, incremental AUC for plasma glucose was higher in the Fragmented + Coffee trial compared with Fragmented. Whilst sleep fragmentation did not alter glycaemic or insulinaemic responses to morning glucose ingestion, if a strong caffeinated coffee is consumed, then a reduction in glucose tolerance can be expected.

Physiological responses to maximal eating in men.

This study investigated metabolic, endocrine, appetite and mood responses to a maximal eating occasion in fourteen men (mean: age 28 (sd 5) years, body mass 77·2 (sd 6·6) kg and BMI 24·2 (sd 2·2) kg/m2) who completed two trials in a randomised crossover design. On each occasion, participants ate a homogenous mixed-macronutrient meal (pizza). On one occasion, they ate until 'comfortably full' (ad libitum) and on the other, until they 'could not eat another bite' (maximal). Mean energy intake was double in the maximal (13 024 (95 % CI 10 964, 15 084) kJ; 3113 (95 % CI 2620, 3605) kcal) compared with the ad libitum trial (6627 (95 % CI 5708, 7547) kJ; 1584 (95 % CI 1364, 1804) kcal). Serum insulin incremental AUC (iAUC) increased approximately 1·5-fold in the maximal compared with ad libitum trial (mean: ad libitum 43·8 (95 % CI 28·3, 59·3) nmol/l × 240 min and maximal 67·7 (95 % CI 47·0, 88·5) nmol/l × 240 min, P < 0·01), but glucose iAUC did not differ between trials (ad libitum 94·3 (95 % CI 30·3, 158·2) mmol/l × 240 min and maximal 126·5 (95 % CI 76·9, 176·0) mmol/l × 240 min, P = 0·19). TAG iAUC was approximately 1·5-fold greater in the maximal v. ad libitum trial (ad libitum 98·6 (95 % CI 69·9, 127·2) mmol/l × 240 min and maximal 146·4 (95 % CI 88·6, 204·1) mmol/l × 240 min, P < 0·01). Total glucagon-like peptide-1, glucose-dependent insulinotropic peptide and peptide tyrosine-tyrosine iAUC were greater in the maximal compared with ad libitum trial (P < 0·05). Total ghrelin concentrations decreased to a similar extent, but AUC was slightly lower in the maximal v. ad libitum trial (P = 0·02). There were marked differences on appetite and mood between trials, most notably maximal eating caused a prolonged increase in lethargy. Healthy men have the capacity to eat twice the energy content required to achieve comfortable fullness at a single meal. Postprandial glycaemia is well regulated following initial overeating, with elevated postprandial insulinaemia probably contributing.

Frequent Carbohydrate Ingestion Reduces Muscle Glycogen Depletion and Postpones Fatigue Relative to a Single Bolus.

The timing of carbohydrate ingestion and how this influences net muscle glycogen utilization and fatigue has only been investigated in prolonged cycling. Past findings may not translate to running because each exercise mode is distinct both in the metabolic response to carbohydrate ingestion and in the practicalities of carbohydrate ingestion. To this end, a randomized, cross-over design was employed to contrast ingestion of the same sucrose dose either at frequent intervals (15 × 5 g every 5 min) or at a late bolus (1 × 75 g after 75 min) during prolonged treadmill running to exhaustion in six well-trained runners (V˙O2max 61 ± 4 ml·kg-1·min-1). The muscle glycogen utilization rate was lower in every participant over the first 75 min of running (Δ 0.51 mmol·kg dm-1·min-1; 95% confidence interval [-0.02, 1.04] mmol·kg dm-1·min-1) and, subsequently, all were able to run for longer when carbohydrate had been ingested frequently from the start of exercise compared with when carbohydrate was ingested as a single bolus toward the end of exercise (105.6 ± 3.0 vs. 96.4 ± 5.0 min, respectively; Δ 9.3 min, 95% confidence interval [2.8, 15.8] min). A moderate positive correlation was apparent between the magnitude of glycogen sparing over the first 75 min and the improvement in running capacity (r = .58), with no significant difference in muscle glycogen concentrations at the point of exhaustion. This study indicates that failure to ingest carbohydrates from the outset of prolonged running increases reliance on limited endogenous muscle glycogen stores-the ergolytic effects of which cannot be rectified by subsequent carbohydrate ingestion late in exercise.