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Combining fasting with exercise may influence gastric emptying rate (GER) and provide benefits to weight management and metabolic health. Furthermore, the time of day in which exercise is performed may also influence these variables. The aim was to investigate if fasting or fed exercise at different times of the day would alter GER, appetite and metabolic responses. Twelve males with overweight completed four experimental trials in a randomised crossover fashion involving cycling exercise in the morning fasted (FASTED‐AM), evening fasted (FASTED‐PM) and after a standardised meal in the morning (FED‐AM) and evening (FED‐PM). GER of a semi‐solid meal was measured using the 13C‐breath test for 2 h. Appetite hormones, metabolic markers and subjective appetite were measured throughout, with energy intake (EI) monitored for the following 24 h. No difference was observed for GER between trials. No differences were seen between trials for appetite hormone responses except pancreatic polypeptide hormone incremental area under the curve (iAUC) was greater in FED‐PM compared to FASTED‐AM and FASTED‐PM (P < 0.05). Glucose concentrations were greater in the postprandial period of FASTED‐PM compared to all trials (P < 0.05). No differences in other metabolic marker responses were seen between trials. GER in individuals with overweight was not sensitive to a diurnal variation following fasted or fed exercise, and an acute bout of fasted exercise did not evoke compensatory effects on appetite responses or 24 h EI. Glucose control may be impaired with FASTED‐PM exercise. Future work is required to assess the long‐term impact of fasted exercise on gastrointestinal function, appetite regulation and metabolic health. What is the central question of this study? Does fasted exercise at different times of the day affect gastric emptying rate, appetite and metabolic responses compared to fed exercise in individuals with overweight? What is the main finding and its importance? The time of fasted exercise did not result in differences in gastric emptying rate compared to fed exercise. However, evening fasted exercise may lead to poorer glucose control during a subsequent meal. Energy intake was not increased in the 24 h following in compensation, therefore, combining fasting with moderate‐intensity exercise may be a potential strategy for weight management practices.

ObjectiveTo investigate the effect of brisk walking in the fasted versus fed state on gastric emptying rate (GER), metabolic responses and appetite hormone responses.Subjects/methodsTwelve healthy men completed two 45 min treadmill walks, fasted (FASTED) and followed consumption of a standardised breakfast (FED). GER of a standardised lunch was subsequently measured for 2 h using the 13C-breath test method. Blood samples were collected at baseline, post-breakfast period, pre-exercise, immediately post exercise, pre-lunch then every 30 min following lunch for 2 h. Circulating concentrations of acylated ghrelin (GHR), glucagon-like peptide-1 (GLP-1), peptide tyrosine tyrosine (PYY), pancreatic polypeptide (PP), glucose, insulin, triglycerides, non-esterified fatty acids (NEFA) and cholesterol were measured. Subjective feelings of appetite were assessed at 15 min intervals throughout. Substrate utilisation was measured every 30 min, and continuously throughout exercise by indirect calorimetry.ResultsNo differences were observed for GER T½ (FASTED 89 ± 22 vs. FED 89 ± 24 min, P = 0.868) nor Tlag (FASTED 55 ± 15 vs. FED 54 ± 14 min, P = 0.704). NEFA concentrations were higher in FASTED at pre-exercise, post exercise and 30 min post exercise (pre-lunch) (all P < 0.05) but no differences were observed for glucose, cholesterol or triglycerides. Carbohydrate oxidation was greater at all time-points during FED exercise (all P < 0.05). Minimal changes in appetite were observed post lunch ingestion with no differences in PYY or GHR observed between trials. GLP-1 concentrations were greater in FED post-breakfast and pre-exercise (P < 0.05), though no differences were observed after lunch. A greater concentration of PP was observed in FED from pre-exercise to 30 min post lunch consumption (all P < 0.05). Insulin concentrations were higher in FED pre-exercise but higher in FASTED 1.5 h post lunch (P < 0.05).ConclusionThese findings suggest that gastrointestinal function, hunger and appetite regulatory hormones are not sensitive to low-intensity bouts of physical activity and holds positive implications for weight management practices.

Diet is integral to the healthy ageing process and certain diets can mitigate prolonged and deleterious inflammation. This review aims to assess the impact of diets high in sustainably sourced proteins on nutrient intake, gut, and age-related health in older adults. A systematic search of the literature was conducted on 5 September 2023 across multiple databases and sources. Studies assessing sustainably sourced protein consumption in community dwelling older adults (≥65 years) were included. Risk of bias (RoB) was assessed using ‘RoB 2.0′ and ‘ROBINS-E’. Narrative synthesis was performed due to heterogeneity of studies. Twelve studies involving 12,166 older adults were included. Nine studies (n = 10,391) assessed habitual dietary intake and had some RoB concerns, whilst three studies (n = 1812), two with low and one with high RoB, conducted plant-based dietary interventions. Increased adherence to sustainably sourced diets was associated with improved gut microbial factors (n = 4640), healthier food group intake (n = 2142), and increased fibre and vegetable protein intake (n = 1078). Sustainably sourced diets positively impacted on gut microbiota and healthier intake of food groups, although effects on inflammatory outcomes and health status were inconclusive. Future research should focus on dietary interventions combining sustainable proteins and fibre to evaluate gut barrier function and consider inflammatory and body composition outcomes in older adults.

Exercise intensity affects many potential postprandial responses, but there is limited information on the influence of exercise modality. Therefore, the aim of this study was to investigate if the nature of exercise at two different intensities would affect gastric emptying rate (GER), appetite and metabolic responses following ingestion of a semi-solid meal. Twelve healthy men completed, in a random order, four 60-min cycles at 60% VO2peak (MOD), 40% VO2peak (LOW) and in a continuous (CON) or intermittent (INT) manner. INT consisted of 20 × 1-min exercise bouts with 2-min rest breaks. INT and CON were matched for total work output at each intensity. GER of the post-exercise meal was measured for 2 h using the 13C-breath method. Blood glucose, substrate utilisation and appetite ratings were measured at regular intervals throughout all trials and 24-h energy intake (EI) post-trials was assessed. GER-Delta over Baseline (DOB) was lower (p < 0.05) on MOD-INT vs. MOD-CON from 30–120 min post-meal. Blood glucose was higher mid-exercise (p < 0.05) on MOD-INT vs. MOD-CON. Although post-exercise LOW-CON was significantly higher than LOW-INT (p < 0.05), blood glucose was also higher 30-min post-meal ingestion on both CON trials compared to INT (p < 0.001). No interaction effect was observed for perceived appetite responses 2 h after meal ingestion (all p > 0.05). 24-h post-trial EI was similar between LOW-CON vs. LOW-INT (p > 0.05), although MOD-INT vs. MOD-CON 3500 ± 1419 vs. 2556 ± 989 kCal: p < 0.001 was elevated. In summary, MOD-INT exercise delays GER without stimulating perceived appetite in the 2 h period after meal ingestion, although EI was greater in the 24-h post-trial.

This study investigated the acute circulating gut hormone, appetite and gastric emptying rate responses to a semi-solid meal following exercise at different intensities. Twelve men completed three trials in a randomised-crossover design, consisting of continuous cycling at 70% V˙O2Peak (HIGH), 40% V˙O2Peak (LOW) or rest (CONTROL). Baseline samples were collected after an overnight fast before undertaking the 60 min exercise or rest period, followed by 30 min rest before consumption of a standardised semi-solid meal (~242 kcal). During the 2 h postprandial period, gastric emptying rate of the meal was examined using the 13C-breath test method, appetite was measured using visual analogue scales, and serum concentrations of acylated ghrelin, pancreatic polypeptide, peptide YY, glucagon-like peptide-1, insulin, glucose, triglycerides, total cholesterol and non-esterified fatty acids were assessed. Subjective appetite response was not different between trials (p > 0.05). Half emptying time of the meal was 89 ± 13, 82 ± 8 and 94 ± 31 min on CONTROL, LOW and HIGH, respectively (p = 0.247). In healthy un-trained adult males, responses to exercise at intensities of 70% and 40% V˙O2Peak did not differ to a non-exercise control for measurements of subsequent gastric emptying, circulating gut hormone response or appetite. These results suggest that exercise intensity has little effect on post-exercise appetite response to a semi-solid meal.

Whey protein is a commonly ingested nutritional supplement amongst athletes and regular exercisers; however, its role in post-exercise rehydration remains unclear. Eight healthy male and female participants completed two experimental trials involving the ingestion of 35 g of whey protein (WP) or maltodextrin (MD) at the onset of a rehydration period, followed by ingestion of water to a volume equivalent to 150% of the amount of body mass lost during exercise in the heat. The gastric emptying rates of the solutions were measured using 13C breath tests. Recovery was monitored for a further 3 h by the collection of blood and urine samples. The time taken to empty half of the initial solution (T1/2) was different between the trials (WP = 65.5 ± 11.4 min; MD = 56.7 ± 6.3 min; p = 0.05); however, there was no difference in cumulative urine volume throughout the recovery period (WP = 1306 ± 306 mL; MD = 1428 ± 443 mL; p = 0.314). Participants returned to net negative fluid balance 2 h after the recovery period with MD and 3 h with WP. The results of this study suggest that whey protein empties from the stomach at a slower rate than MD; however, this does not seem to exert any positive or negative effects on the maintenance of fluid balance in the post-exercise period.

Subjects then rehydrated with 150% of their body mass loss over 1 h. During rehydration subjects ingested bottled mineral water (W) or mineral water+20 g.l−1 whey protein isolate (WP) in a double blind randomised, counterbalanced order. Whilst protein ingestion increased plasma albumin content, which was likely responsible for the increase in plasma volume 3–4 h post-drinking in WP, it appears that this increased oncotic pressure was not sufficient to reduce the diuresis associated with ingesting a large volume of drink in a short time period. Post-exercise nutritional requirements are often multifactorial (rehydration, glycogen resynthesis, muscle protein synthesis) and the present data demonstrates that when post-exercise protein intake might benefit recovery or adaptation, this can be achieved without compromising rehydration. 1.

The global prevalence of obesity has dramatically increased and has become a major economic burden for western countries; therefore, health professionals are looking at strategies to control this increase in body weight. Despite the well-established physiological effects of exercise, such as increased muscle oxygenic capacity and fuel utilisation being well documented, there is limited research available investigating how the human body responds to a change in exercise characteristics. Manipulating exercise intensity, mode, or timing has become a popular strategy for controlling metabolic health and might support improved weight management programs. The ability of the human body to respond to nutritional intervention after exercise may determine how fat stores are regulated and in what manner the body responds postprandially. This may hold the key to how the body recovers and adapts after exercise, however, this area of research remains ambiguous. Through a series of studies on human volunteers this thesis is aimed at enhancing our understanding of how different exercise characteristics (intensity, mode, or timing) might affect gastrointestinal function, metabolic responses, appetite, and energy intake (EI), and as a result support the development of novel non-pharmacological interventions for weight management. The main findings of this thesis were as follows. Gastric emptying rate (GER) is similar 30 min after continuous and intermittent exercise at a low intensity (40% V̇O2peak) and at a moderate intensity (60% V̇O2peak). Repeated bouts of continuous exercise cause food within the stomach to empty faster when compared to a one-off exercise bout matched at a high intensity of 70% V̇O2peak. Intermittent exercise > 40% V̇O2peak and continuous exercise > 60% V̇O2peak reduces subjective feelings of hunger immediately post-exercise. Although, continuous exercise < 50% V̇O2peak has no effect. A subsequent meal following both intermittent and continuous exercise at various intensities abolishes any compensatory effects in subjective feelings of hunger. Acylated ghrelin increases immediately after continuous exercise < 50% V̇O2peak whereas continuous exercise > 70% V̇O2peak and intermittent exercise at peak power output (PPO) decreases acylated ghrelin. Furthermore, postprandial acylated ghrelin increases after multiple exercise bouts compared to a one-off continuous bout at the same intensity, although this also leads to an increase in EI within the first 24-h. EI was also found to be increased after moderate intensity intermittent exercise. Intermittent exercise >40% V̇O2peak increases blood glucose during and immediately after exercise. Conflicting evidence revealed continuous exercise triggered a spike in blood glucose after a calorific meal more so than intermittent exercise causing blood glucose to remain elevated during recovery periods. Substrate utilisation shifts to predominantly fat oxidation after continuous and intermittent exercise at various intensities between 40- 70% V̇O2peak while a small calorific meal diminishes this increase in the postprandial period. The role of manipulating exercise characteristics through intensity, mode, or timing may hold positive implications for weight management practices in healthy and overweight populations. Future work is warranted to investigate the influence of ingesting whole foods/meals after exercise to better recognise the changes during the postprandial period; on GER, appetite, and appetite regulatory hormones over an extended duration to explore the effects on energy balance and metabolic health in the long-term.

Studies have examined adding protein to carbohydrate–electrolyte rehydration drinks, but the effects of protein in isolation remain unknown. Ten subjects completed two trials in which they were dehydrated (~2 % of pre-exercise body mass) by intermittent cycling in the heat. Subjects then rehydrated (150 % total mass loss) over 1 h with mineral water (W) or mineral water plus 20 g L⁻¹whey protein isolate (WP) and remained in the laboratory for a further 4 h. Blood and urine samples were provided pre-exercise, post-exercise, post-rehydration and every hour thereafter. From blood samples, serum osmolality, change in plasma volume and plasma albumin content was determined, whilst the volume and osmolality of urine samples were determined. There was no difference between trials for total urine volume [W: 1,234 (358) mL; WP: 1,306 (268) mL; P = 0.409], drink retention [W: 40 (14) %; WP: 37 (14) %; P = 0.322] or net fluid balance [W: −605 (318) mL; WP: −660 (274) mL; P = 0.792] 4-h post-rehydration. Plasma volume was greater 3 and 4 h post-drinking during WP, and plasma albumin content relative to pre-exercise was increased 1–4 h post-drinking in WP only. These results suggest that addition of 20 g L⁻¹whey protein isolate neither enhances nor inhibits post-exercise rehydration, when a volume equivalent to 150 % of sweat losses is ingested in 1 h. As post-exercise nutritional requirements are multifactorial (rehydration, glycogen resynthesis, myofibrillar/mitochondrial protein synthesis), these data demonstrate that when post-exercise protein intake might benefit recovery or adaptation, this can be achieved without compromising rehydration.