Gastrointestinal Function and Metabolic Responses to Fasted Exercise; Implications for Food, Energy Intake and Obesity

McIver, Victoria Joan (2020) Gastrointestinal Function and Metabolic Responses to Fasted Exercise; Implications for Food, Energy Intake and Obesity. Doctoral thesis (PhD), Manchester Metropolitan University.

Preview

Available under License Creative Commons Attribution Non-commercial No Derivatives. Download (3MB) | Preview

Abstract

The increasing economic burden confronted by nation-states in the face of a global obesity epidemic is well documented. Intermittent fasting has become a popular intervention for metabolic health and combining intermittent fasting with exercise may support weight management programming. Therefore, fasted exercise has become an increasingly popular strategy in weight management practices. However, the effects of fasted exercise on gastrointestinal function, metabolic markers, and appetite regulation remains unclear. This thesis aimed to enhance understanding of fasted versus fed exercise on gastrointestinal function, metabolic responses, and appetite. This will support the development of novel nonpharmacological interventions for weight management. A series of studies on human volunteers are presented in this thesis. Firstly, the effect of brisk walking in the fasted versus fed state on the gastric emptying rate (GER), metabolic responses and appetite hormone responses in healthy men were determined. These findings suggest that GER, hunger and appetite regulatory hormones are not sensitive to low-intensity bouts of physical activity and, that fasted brisk walking holds positive implications for weight management practices. Following on from these findings, the diurnal influences of GER, appetite and metabolic responses when performing fasted and non-fasted exercise in healthy men was assessed. The findings suggest that evening fasted exercise delays GER, without changes in appetite. No compensatory effects were observed for appetite following fasted exercise and regardless of the time of day, fasted exercise induces a negative energy balance without a subsequent compensatory response in energy intake (EI). Following on from these results, the diurnal influences were further explored by measuring gastrointestinal hormones and metabolites, as well as GER and appetite following fasted versus non-fasted exercise in lean men. These findings suggested GER is slower in the evening; with subtle differences observed in hormonal and metabolic responses. No compensatory effects were found for appetite post-exercise or 24 h EI post-trial. To understand if these findings were consistent within other population groups, the study was repeated in overweight men. No differences were found in all variables. Overall, the findings within this thesis suggest fasted exercise may hold positive implications for weight management practices in healthy, lean, and overweight populations. Future work is required to assess the long-term effects of fasted exercise on metabolic health, energy balance and gastrointestinal function.