ECSS Paris 2023: CP-PN19
INTRODUCTION: Heat stress has been shown to decrease exogenous glucose oxidation rates during exercise by approximately 10%. There is some evidence that manipulating the gut microbiome via probiotic supplementation may increase exogenous carbohydrate oxidation rates during exercise. We aimed to assess whether a prebiotic galactooligosaccharide supplement can increase exogenous glucose oxidation rates during moderate-intensity exercise in either temperate or hot environments. METHODS: 22 trained cyclists (14 males, 8 females; age = 43 ± 13 years; VO2peak = 50 ± 8 mL/kg/min) completed a preliminary trial (lactate threshold, VO2peak and 1-hour familiarisation) and four experimental trials. Participants supplemented daily with 3.65 g of maltodextrin placebo (PLA) or Bimuno-galactooligosaccharide (B-GOS) mixture for 4 wk (separated by a 4 wk washout period) in a randomised, double-blind, crossover design. After each supplement period, participants completed two experimental trials, which involved 2h cycling at 95% LT1 in 21°C (TEMP) and 35°C (HOT) ambient temperatures. A glucose drink containing [U-13C]-glucose was consumed every 15 min providing 90 g/h and exogenous glucose oxidation rates were determined over a 30-120 min period. Gastrointestinal (GI) symptom scores were recorded every 30 min during exercise and were analysed individually, grouped into upper (nausea, regurgitation, fullness & cramps) and lower (gas & urge to defecate) GI categories, and as mean total scores. RESULTS: Total exogenous glucose oxidation was lower in PLA HOT vs. PLA TEMP (19 ± 11 g/h vs. 30 ± 10 g/h; P < 0.001, respectively). In contrast, there was no evidence B-GOS meaningfully increased total exogenous glucose oxidation (TEMP: PLA 30 ± 10 g/h vs. B-GOS 30 ± 9 g/h; P = 0.512; and HOT: PLA 19 ± 11 g/h vs. B-GOS 21 ± 14 g/h; P = 0.081). In TEMP, GI symptom scores for nausea (P = 0.017), upper (P = 0.026), and mean total (P = 0.020) were lower for B-GOS. No differences were evident for all other individual symptoms or lower GI (P > 0.05). Total carbohydrate and fat oxidation were not different between PLA and B-GOS (P > 0.05); however, total fat oxidation was lower in PLA HOT vs. PLA TEMP (P = 0.023). Plasma insulin concentrations were not different between PLA and B-GOS, or between temperatures (P > 0.05). Glucose and lactate concentrations were not different between PLA and B-GOS (P > 0.05), but lactate concentrations were higher in the heat (P = 0.048). CONCLUSION: We provide evidence that heat stress can decrease exogenous glucose oxidation rates during moderate-intensity exercise by a greater magnitude (37%) than previously seen. Therefore, athletes and practitioners should carefully consider fuelling strategies in the heat, and explore approaches to mitigate reduced exogenous fuel availability in hot environments. Whilst B-GOS supplementation may provide some symptomatic relief in temperate conditions, other strategies will probably be required to address fuel availability limitations.
Read CV Adam CollinsECSS Paris 2023: CP-PN19
INTRODUCTION: Late-dinner eating (LD) impairs postprandial metabolism (e.g., glucose regulation and insulin sensitivity). Studies have indicated that a bout of moderate-intensity aerobic exercise can enhance glucose tolerance and/or insulin sensitivity; however, it remains unknown whether aerobic exercise can modulate the impaired metabolic responses due to LD. This study examined the effects of moderate-intensity aerobic exercise prior to LD on postprandial glycaemic regulation and gut hormone responses (GLP-1, PYY and GIP) the following morning. METHODS: 14 young healthy men (age: 26.2 ± 4.9 years, BMI: 22.8 ± 2.5 kg/m2) completed 3 trials across 2 days including (1) regular dinner (RD at 18:00), (2) late dinner eating (LD at 21:30) and (3) 45-minute brisk walking at 60%V̇O2max + late dinner at 21:30 (ELD), in a randomized crossover study design. A 2-hour OGTT was conducted in the following morning, with blood (plasma) samples collected at baseline, and every 15 min following glucose ingestion. The primary outcome was total glucose area under the curve (tAUC) over the 120-min sampling period. One-way ANOVA were applied and the significant level is α = 0.05. RESULTS: In the ELD trial, exercise intensity was 62 ± 2 %V̇O2max, with an average energy expenditure of 408 ± 61 kcal during 45 min exercise. The average heart rate reached to 143 ± 10 bpm, accompanying by a RPE of 12 ± 2. During a 2-h OGTT, tAUC for glucose (833 ± 182 vs. 826 ± 133 vs. 859 ± 196 mmol/2 h/L, respectively) and insulin (27.2 ± 21.3 vs. 28.2 ± 15.7 vs. 28.9 ± 16.2 nmol/2 h /L, respectively) concentrations were not different between RD, LD and ELD trials (all, p > 0.05). In addition, GLP-1, PYY and GIP concentrations did not differ between 3 trials (all, p > 0.05). CONCLUSION: In the healthy young males, late dinner eating did not acutely result in the impairment of glucose control and insulin sensitivity. Moreover, acute bout of exercise performed immediately prior to late dinner eating did not influence glucose control and insulin sensitivity next morning. Dinner timing with and without exercise did not affect gut hormone (GLP-1, PYY and GIP) responses.
Read CV Yung-Chih ChenECSS Paris 2023: CP-PN19
INTRODUCTION: Long-haul flights involving transition between time-zones may misalign the human circadian timing system and impair metabolic regulation. We hypothesised that modifying meal patterns for 7 days before departure to match destination eating times would minimise metabolic disruption evident both one day and one week following arrival. This may have implications for the metabolic health of individuals traveling long distances, including athletes who regularly cross time-zones for international competition. METHODS: Between May 2019 and May 2022, twenty-five young women (n=18) and men (n=7) who were lean and metabolically healthy (age = 21±1 years, height = 1.70±0.11 m, body mass = 67.9±12.8 kg, body mass index = 23.3±2.6 kg·m-2; means ± standard deviation) and residing in California, USA, were randomly allocated to adhere to one of two dietary patterns over the 7 days prior to a ~10.5 h transatlantic flight to the UK. The control group ate according to their local time zone (Pacific Daylight Time; PDT), with a typical breakfast consumed from 0600-0700 h, a typical lunch from 1200-1300 h and a typical dinner from 1800-1900 h; whereas the intervention group ate in the same pattern but with timings shifted by 6-8 hours to broadly match their destination time-zone (British Summer Time; BST), with a typical lunch therefore consumed from 0600-0700 h, a typical dinner from 1200-1300 h and a typical breakfast meal from 2300-0000 h (all local time; PDT). All participants went to bed at 2300-0000 h and woke at 0600-0700 h. Oral glucose tolerance tests were completed in California 12 days prior to the transatlantic flight, then 24-h and 168-h after arrival in the UK. RESULTS: Both groups exhibited elevated glycaemic responses to the oral glucose tolerance tests upon arrival in the UK relative to their baseline assessments in California (ANOVA time effect p=0.003), but without any significant difference in the magnitude of this effect between experimental conditions (ANOVA interaction p=0.093). Specifically, the respective blood glucose concentration incremental area under curve for the control and interventions at baseline were 210±65 and 216±107 mmol·120 min·l-1, 24 hours after arrival were 295±115 and 331±102 mmol·120 min·l-1, and 168 hours after arrival had recovered to 193±75 and 244±83 mmol·120 min·l-1. Peak blood glucose concentrations followed similar numeric patterns, broadly reflecting an increase >0.5 mmol·l-1 from baseline to 24-h (with partial recovery by 168-h), also with no difference between experimental conditions. Fasted glucose concentrations were relatively stable across all testing days in both groups. CONCLUSION: This is the first study to examine changes in oral glucose tolerance before and after transatlantic travel, with significant impairment 24-h after the time-zone transition. This effect was not mitigated even by a relatively extreme schedule of eating according to the destination time-zone for a full week prior to departure.
Read CV Lucy MerrellECSS Paris 2023: CP-PN19