Effects of an acute bout of aerobic exercise on immediate and subsequent three-day food intake and energy expenditure in active and inactive pre-menopausal women taking oral contraceptives

This study examined the effects of an acute bout of exercise of low-intensity on food intake and energyexpenditure over four days in women taking oral contraceptives. Twenty healthy, active (n = 10) and inactive (n = 10) pre-menopausal women taking oral contraceptives completed two conditions (exerciseand control), in a randomised, crossover fashion. The exercise experimental day involved cycling for onehour at an intensity equivalent to 50% of maximum oxygen uptake and two hours of rest. The controlcondition comprised three hours of rest. Participants arrived at the laboratory fasted overnight; breakfast was standardised and an ad libitum pasta lunch was consumed on each experimental day. Participantskept a food diary to measure food intake and wore an Actiheart to measure energy expenditure for theremainder of the experimental days and over the subsequent 3 days. There was a condition effect forabsolute energy intake (exercise vs. control: 3363 ± 668 kJ vs. 3035 ± 752 kJ; p = 0.033, d = 0.49) and relative energy intake (exercise vs. control: 2019 ± 746 kJ vs. 2710 ± 712 kJ; p < 0.001, d = −1.00) at the adlibitum lunch. There were no significant differences in energy intake over the four days in active participants and there was a suppression of energy intake on the first day after the exercise experimental daycompared with the same day of the control condition in inactive participants (mean difference = −1974 kJ;95% CI −1048 to −2900 kJ, p = 0.002, d = −0.89). There was a group effect (p = 0.001, d = 1.63) for free-living energy expenditure, indicating that active participants expended more energy than inactiveparticipants during this period. However, there were no compensatory changes in daily physical activity energy expenditure. These results support the use of low-intensity aerobic exercise as a method toinduce a short-term negative energy balance in inactive women taking oral contraceptives.