Exercise, Hunger, and Gender Differences

Summarized by Robert W. Griffith, MD
January 7, 2005

Introduction

Most studies of the effects of exercise on food intake have been done in men. Although one might expect intense exercise to stimulate appetite, studies done to date have shown that it actually causes a brief suppression of hunger. But, as we've said, these studies were done chiefly in men. Canadian researchers wanted to find out if things are the same in women. The results of their study have been published in the American Journal of Clinical Nutrition.

What was done

Young women were recruited at the University of Ottawa. They had to be healthy, 18 to 30, not pregnant, stable in weight, and not taking any medications or following a special diet. At baseline their height, weight, waist, and body fat were determined, and a food questionnaire was administered that included a scale that assessed hunger.

An aerobic capacity test was done to measure maximum oxygen consumption (VO2max); it comprised gradually increased aerobic treadmill exercise with measurement of heart and respiratory function. Subjects were then tested at three levels of exercise: no exercise, low intensity (40% of peak oxygen uptake), and high intensity (70% of peak oxygen uptake). The duration of exercise in the 2^nd and 3^rd test was adjusted to result in an energy expenditure of approximately 350 calories; the average durations at low- and high-intensity exercise were 65 minutes and 37 minutes, respectively.

Each participant took all three tests, in a randomly-assigned order, at approximately 4-week intervals. They had a standardized diet for 3 days before each test, which started with a basic metabolic rate measurement at 8:00 am, followed by a standard breakfast. At 10:00 am the exercise test was done, and then the subjects were offered a buffet-lunch at noon, and a buffet-dinner at 5:30 pm. Snacks were offered at 3:30 pm and 8:00 pm. The participants were allowed to eat as much as they wanted. They also completed a scoring system to assess how hungry they felt at various time points throughout the day.

What was found

Significantly more food was eaten at lunch after high-intensity exercise than after no exercise - averages of 878 calories vs. 751 calories, respectively. There was no significant difference with low-intensity exercise, and no exercise effects on the amount of dinner eaten were found.

The amount of calories consumed during the test days showed an increase with low- and a greater increase with high-intensity exercise, but the differences were not statistically significant - i.e. they could have occurred by chance alone. The average daily calorie intakes were: no exercise: 2285, low-intensity: 2397, and high-intensity: 2580 calories.

There were no exercise-related changes in appetite scores on the questionnaires or on the scales used to reflect hunger during the test days.

What this means

The authors of this study had expected a different result. Intense exercise in men is linked to a decrease in appetite, and the investigators wanted to see if this could be confirmed in women. What they found was that high-intensity exercise was associated with an increased energy intake at a meal two hours later. This effect, in fact, corresponds to our natural expectations - more exercise equates with increased appetite.

What's the reason for this gender difference? The investigators did an additional calculation - the actual energy balances for the three tests. In fact, the energy balance at lunchtime after both the low- and high-intensity exercise in the women was lower than after the control session. This suggests that exercise in women produces a negative energy balance more rapidly than in men, and that low-intensity exercise is better at this. Perhaps this explains the recent reports that women who walk for 30 minutes a day have good results in controlling their weight.

Apart from demonstrating (once again) that women are different from men, the findings show that, at least for women, low intensity exercise has a similar, or better, effect on energy balance than high-intensity exercise. Whether you think that's important or not, it's clear that any form of exercise is better than none.

Source

• Effects of exercise intensity on food intake and appetite in women. M. Pomerleau, P. Imbeault, T. Parker, E. Doucet, Am J Clin Med, 2004, vol. 80, pp. 1230--1236

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