Effects of exercise on appetite, food intake and the gastrointestinal hormones Ghrelin and Peptide YY

Gut hormones are implicated in the regulation of energy balance. The studies in this thesis have examined the effects exercise on gut hormones (acylated ghrelin and peptide YY3-36), appetite and food intake, over extended durations. Sixty-nine young, healthy, predominantly Caucasian males were recruited to six studies. The age, height and body mass of the participants were: 22.4 ± 0.3 y, 1.80 ± 0.1 m, 76.2 ± 1.0 kg (mean ± SEM). In study one, 90 min of resistance exercise did not influence appetite or energy intake over 24 h of assessment, yet stimulated a latent preference for carbohydrate rich foods. Study two demonstrated that appetite was suppressed during 60 min of swimming but was elevated after consuming a post-exercise meal. Plasma acylated ghrelin was suppressed during swimming but was unaltered after. Energy/macronutrient intake remained unchanged. In study three, 60 min of brisk walking (45 ± 2% of max) did not influence appetite, energy/macronutrient intake or plasma concentrations of acylated ghrelin during an eight hour observation period. Study four showed that 90 min of treadmill running (69 ± 1% of max) transiently suppressed appetite and acylated ghrelin but did not influence these variables, or energy/macronutrient intake within 22.5 h after exercise. The findings of study five suggest that the suppression and subsequent rebound in plasma acylated ghrelin after exercise may be related to a delayed voluntary decision to eat after. Finally, study six showed that appetite, food intake and circulating concentrations of acylated ghrelin and peptide YY3-36 are responsive to acute deficits in energy induced by food restriction but are not sensitive to equivalent energy deficits induced by exercise. This thesis has shown that exercise transiently alters circulating levels of acylated ghrelin and peptide YY3-36 in directions expected to inhibit appetite however no changes are seen after exercise. Conversely, food restriction elicits marked compensatory changes in circulating acylated ghrelin and peptide YY3-36. This thesis also demonstrates that resistance exercise, brisk walking and running do not stimulate appetite or energy intake over defined periods, even when the energy expenditure elicited is high. Swimming appears to increase appetite in the latter hours after exercise.