Effect of increased physical activity on voluntary intake in lean women.

To determine the effect of exercise-related factors on food intake, five nonobese women (mean +/- SEM of the percent of desirable body weight, 97 +/- 5) were hospitalized as part of a metabolic experiment. Excess amounts of a mixed food diet were provided on platters to the subjects. They served themselves from these and ate freely. Intake was estimated covertly by weighing the platters before and after serving. Expenditure was monitored with daily activity diaries and indirect calorimetry determinations of all the activities recorded. After a five-day evaluation phase, each subject underwent three 19-day treatment periods in which physical activity was modified. Total daily expenditure was increased to 114 +/- 4% of the sedentary treatment for a mild exercise period and 129 +/- 3% for a moderate period. Corresponding voluntary intakes during exercise were 117 +/- 5% and 122 +/- 6% of sedentary treatment. Although moderate exercise (mean 772 +/- 40 kcal/d) was greater than mild (378 +/- 63 kcal/d), the increased intake levels of the two were comparable. However, the resulting energy balances of 10 +/- 71 kcal/d for sedentary, 64 +/- 43 kcal/d for mild and -116 +/- 92 kcal/d for moderate treatments were not different. Therefore, in a paradigm which permits maintenance of a voluntary balanced energy state during an inactive period, compensatory intake responses to exercise occur. Unlike obese women who do not match their intakes to energy expended as physical activity, nonobese women demonstrate hyperphagic responses.