Effect of moderate physical activity on plasma leptin concentration in humans

In subjects who maintain a constant body mass, the increased energy expendi ture induced by exercise must be compensated by a similar increase in energ y intake. Since leptin has been shown to decrease food intake in animals, i t can be expected that physical exercise would increase energy intake by lo wering plasma leptin concentrations. This effect may be secondary either to exercise-induced negative energy balance or to other effects of exercise. To delineate the effects of moderate physical activity on plasma leptin con centrations, 11 healthy lean subjects (4 men, 7 women) were studied on thre e occasions over 3 days; in study 1 they consumed an isoenergetic diet (1.3 times resting energy expenditure) over 3 days with no physical activity; i n study 2 the subjects received the same diet as in study 1, but they exerc ised twice daily during the 3 days (cycling at 60 W for 30 min); in study 3 the subjects exercised twice daily during the 3 days, and their energy int ake was increased by 18% to cover the extra energy expenditure induced by t he physical activity. Fasting plasma leptin concentration (measured on the morning of day 4) was unaltered by exercise [8.64 (SEM 2.22) 7.17 (SEM 1.66 ), 7.33 (SEM 1.72) 1 mu g . l(-1) in studies 1, 2 and 3, respectively]. It was concluded that a moderate physical activity performed over a 3-day peri od does not alter plasma leptin concentrations, even when energy balance is slightly negative. This argues against a direct effect of physical exercis e on plasma leptin concentrations, when body composition is unaltered.