Effects of exercise on hunger, food intake and energy expenditure

Research in this thesis has examined the acute and chronic effects of exercise on hunger, energy intake and expenditure. Cross-sectional studies examined the effect of 60 min of moderate-intensity cycling on immediate and subsequent three day energy intake and expenditure in active and inactive men (study one) and women not using hormonal contraceptives (study two) and taking oral contraceptives (study three). Study four examined the effects of 12 weeks of moderate-intensity aerobic exercise on 7-day free-living energy intake and expenditure. A total of 47 men (mean ± SD; age 23.8 ± 4.2 y; body mass index 24.2 ± 3.0 kg-m'2) and 52 women (22.7 ± 3.4 y; 22.1 ± 2.1 kg-m'2)were recruited into four studies. In study one, 60 min of moderate-intensity (50% of maximum oxygen uptake) cycling did not have an effect on hunger or ad libitum lunch energy intake (p > 0.05) but induced an acute (within the experimental day, p = 0.024, d = 0.56) and delayed (third day after the experimental day,/> = 0.024, <i= 0.80) increase in free-living energy intake in active and inactive participants, respectively with no compensatory changes in freeliving energy expenditure (p > 0.05). Similarly, studies two and three demonstrated that an acute bout of moderate-intensity aerobic exercise does not increase hunger or ad libitum lunch energy intake in active and inactive women {p > 0.05). In study two there were no exercise-induced compensatory responses in free-living energy intake {p > 0.05) whereas in study three, the inactive group decreased their daily energy intake on the first day after the exercise experimental day compared with control (p = 0.002, d = -0.89). No compensatory changes in daily physical activity energy expenditure were observed in these studies (p > 0.05). In study four 12 weeks of moderate-intensity aerobic exercise did not induce changes to weekly free-living energy intake and expenditure (p > 0.05) despite the high inter-individual variability in changes in body composition. Additionally, inactive participants are not able to independently maintain their physical activity behaviour after the end of a supervised exercise intervention. Overall, this research shows that an acute bout of moderate-intensity aerobic exercise did not affect hunger irrespective of sex or habitual physical activity, however the use of oral contraceptives may have heightened appetite in women. Active men were able to compensate for the acute exercise-induced energy deficit by increasing their energy intake quicker (within the experimental day) than inactive men (third day after the experimental day). In women, no clear relationship was apparent. Moreover, an acute bout of exercise did not elicit compensatory changes in physical activity in men and women. These findings enhance the knowledge of how an acute bout of exercise affects immediate and subsequent energy intake and expenditure in active and inactive men and women but more work is needed to confirm and explore the potential causal mechanisms.