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Logo of jcinvestThe Journal of Clinical InvestigationCurrent IssueArchiveSubscriptionAbout the Journal
J Clin Invest. 1969 November; 48(11): 2124–2128.
PMCID: PMC297466

Effects of weight changes produced by exercise, food restriction, or overeating on body composition


The body weight of rats was reduced by exercise or by restriction of food intake over a period of 18 wk. Body composition was studied to determine if exercise protects against the loss of lean tissue that can occur as a result of a negative caloric balance.

Rats weighing 706 ±14 g were divided into four groups matched for weight. A baseline group was killed at the beginning of the study. An exercising group, fed ad lib., was subjected to a program of swimming. A sedentary, free-eating group was provided with food ad lib. Two sedentary, paired-weight subgroups were calorie restricted so that they lost weight at the same rate as the exercisers. The protein intake of one paired-weight subgroup was matched with that of the exercising group. The other sedentary, paired-weight animals ate the standard diet.

There was no significant difference in body composition between the two sedentary, paired-weight subgroups which were, therefore, pooled for comparison with the other groups. The exercisers lost 182±19 g as a result of both an increase in caloric expenditure and a decrease in appetite. The sedentary, food-restricted animals lost an average of 182±18 g. The sedentary, free-eating animals gained 118±13 g. The carcasses of the exercised animals contained significantly less fat and more lean tissue than those of the sedentary, paired-weight animals, providing evidence for a fat mobilizing and protein conserving effect of exercise. The composition of the body substance lost by the exercising animals was 78% fat, 5% protein, 1% minerals, and 16% water, compared to 62% fat, 11% protein, 1% minerals, and 26% water for the sedentary, food-restricted rats. Fat accounted for 87% and water for 10% of the weight gained by the sedentary, free-eating animals.

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