Acute effects of exercise on appetite, food intake and circulating concentrations of gastrointestinal hormones

Recent years have witnessed significant research into the acute effects of exercise on appetite, energy intake and gut hormone responses. The experiments in this thesis have further investigated this topic by examining the appetite, acylated ghrelin, peptide YY and energy intake responses to energy deficits induced via different exercise protocols and food restriction. To achieve this, 48 young healthy males (mean (SD): age 23 (3) years, body mass index 23.7 (2.7) kg.m-2, maximum oxygen uptake 52.9 (9.8) mL.kg 1.min-1) were recruited into four studies. In study one, 60 min of treadmill running at 70% of VO2 max did not stimulate any increases in appetite or daily energy intake regardless of whether the exercise was performed after breakfast or in the fasted state. In study two, six 30 s Wingate tests stimulated increases in appetite during the subsequent hours compared with 60 min of cycling at 68% of VO2 max. Differences in appetite appeared to be unrelated to changes in plasma acylated ghrelin concentrations and did not influence ad libitum energy intake. Subsequently, endurance exercise resulted in a significantly greater negative daily energy balance than sprint exercise due to a larger exercise energy expenditure. Study three revealed that appetite and energy intake did not differ from a resting control trial after either ten, 4 min cycling bouts at 85 90% of VO2 max separated by 2 min of rest or 60 min of constant cycling at 60% of VO2 max. This occurred despite elevated PYY3-36 concentrations during the hours after exercise. Finally, study four showed that an energy deficit of ~1475 kJ stimulated increases in appetite when induced via food restriction but not when achieved by an acute bout of exercise. This was associated with differences in plasma PYY3-36 concentrations but did not appear to be related to changes in circulating levels of acylated ghrelin and did not influence energy intake. This thesis has shown that appetite perceptions do not differ from a resting control trial during the hours after continuous endurance exercise. Alternatively, supramaximal cycling exercise and subtle reductions in food intake stimulated increases in appetite during the subsequent hours. Such increases in appetite do not appear to be related to changes in acylated ghrelin but may be influenced by plasma PYY3-36 concentrations. Despite differences in appetite, daily energy intake was unaffected by all interventions.