Acute effects of exercise on food intake in obese and nonobese women

Article Abstract:

Even though it is generally accepted that exercise is an effective way to lose weight, there is still much to be learned about the effects of exercise on appetite and food consumption. Some studies suggest that obese and thin individuals may differ in their response to exercise. For example, it was found that over the long term, nonobese women increased their energy consumption appropriately to support increased exercise, but obese women did not do so. Responses to exercise over the short term may be quite different. Studies with animals have shown that their appetites are depressed immediately after strenuous exercise, and a study was designed to test this relationship in obese and thin human subjects. Eighteen young women participated; nine were obese and nine were at or close to their desirable weight for height. The amount of a liquid meal that each woman consumed under three different conditions was measured. The conditions were: strenuous exercise for 40 minutes; moderate exercise for 40 minutes; and resting. The mode of exercise was riding a stationary bicycle. The nonobese women drank significantly less of the liquid meal after exercising strenuously than after moderate exercise, but the obese women consumed the same amount after exercising strenuously as after moderate exercise. The energy expended during exercise and the average heart rate did not differ between the two groups, suggesting that the groups exercised with equal intensity. It was concluded that nonobese women do reduce their food intake immediately after strenuous exercise, as has been seen in laboratory animals. The results for the obese women support other studies of obese persons in suggesting that they are less likely to adjust their food intake appropriately when energy needs change. (Consumer Summary produced by Reliance Medical Information, Inc.)

Causes of, Anorexia nervosa, Exercise, Exercise physiology, Appetite, Appetite (Psychophysiology)

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Comparison of thermic effects of constant and relative caloric loads in lean and obese men

Article Abstract:

Obese persons may have impaired thermogenesis, which is body heat production or energy expenditure, in response to certain stimuli. One such stimulus is eating a meal; normally, following a meal, metabolic rate and energy expenditure rise temporarily. Some studies have found that in obese individuals, this thermic effect of food is smaller than in lean persons, while other studies have not found any difference between lean and obese individuals. The results of previous research projects may be contradictory because the way meal size was determined varied from study to study. The meal size, or caloric load, can be the same for all subjects or it can be based on individual factors such as body weight or metabolic rate. Two methods of determining meal size were used to evaluate whether postprandial (i.e., after a meal) thermogenesis is impaired in obese persons. Eleven lean and eleven obese men participated; they were healthy and between the ages of 25 and 39. Their thermic responses to a meal with a caloric load of 720 calories and also to a meal that represented 35 percent of their individual resting metabolic rates were measured. For both types of meals, the thermic effect of food was greater in the lean subjects than the obese subjects. The type of meal was found to influence thermogenesis. These results support the theory that thermogenesis is defective in obese persons. Thermogenesis may be blunted in obesity because of alterations in the metabolism of insulin and glucose. (Consumer Summary produced by Reliance Medical Information, Inc.)

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Decreased thermic effect of a mixed meal during overnutrition in human obesity

Article Abstract:

The thermic effect of a meal (TEM), also known as thermogenesis, is the physiologic increase in energy expenditure that follows every meal. TEM occurs because calories are used by the gastrointestinal tract, which contracts during and after a meal, and the heart and lungs, which also work harder. Metabolic reactions involved in utilizing and storing nutrients require energy as well. Some researchers have suggested that obese individuals may have altered TEM. Six lean male subjects who reported difficulty gaining weight were compared with six subjects who had a lifelong history of obesity; the obese volunteers included five women and one man. The effect of short-term overfeeding and underfeeding on TEM was assessed. Subjects were admitted to a metabolic research center where the amount of calories required to maintain each individual's weight was determined over 14 days. The participants were then overfed by 1,000 calories daily for 18 days, and then only the obese subjects were underfed for 18 days on a total of 593 calories/day. The temporary overfeeding reduced TEM in the obese but not the lean subjects; thus obese individuals burned less energy in response to the meal when they overate. This is consistent with other studies that suggest spontaneously obese individuals gain weight more easily from overeating than do lean individuals. While differences in TEM are not large enough to cause obesity, they may contribute to the problem.

Health aspects, Measurement, Body temperature, Metabolic regulation

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