A meta-analysis 1 sought to answer the question "does exercising help to maintain the fat-free mass (FFM) of the body in overweight subjects during dieting" (low-energy diet) (i.e. should physical activity be included in the treatment).
Medline search covered the years 1966-93. The studies were not limited to randomised, controlled studies, but all study designs with at least two concurrent intervention groups (not necessarily control groups or randomisation) were included in the analysis. In at least one study the aim of physical training was to reduce the amount of fat tissue. Body composition was assessed with various methods (underwater weighing, skinfolds, bioimpedance, total-body potassium or water, nitrogen equilibrium).
Twenty-eight studies were qualified, with altogether 226 rather sedentary men in 13 groups and 199 women in 23 groups and 233 physically active men in 14 groups and 258 women in 28 groups. BMI or the amount of fat tissue was not defined clearly in the inclusion criteria.
Mean BMIs in different groups were 25-31, and thus clearly obese subjects were not included. In the analyses endurance and resistance training have been assessed separately as have been weight-maintaining diets, small energy restriction and low-energy diets.
In men endurance training without a restriction of energy intake caused on average a 2.6-kg reduction in weight in 30 weeks compared with the non-training group in which the change was +0.4 kg. The corresponding changes in women were -1.4 kg for the exercising group and -0.7 kg for the sedentary group in 12 weeks. No changes of fat-free mass (FFM) were observed. Resistance training had very little effect on weight; however, FFM increased by about 2.1 kg in men and by 1.1 kg in women.
On the basis of regression analysis it was estimated that a diet-induced weight loss of 10 kg causes a 2.9 kg loss of FFM in men and a 2.2 kg loss in women. If the same weight loss were achieved with exercising combined with reduced energy intake the presumed loss of FFM is reduced to 1.7 kg in both men and women.
Comment: Endurance training causes a small or moderate weight loss without a limitation of dietary intake. Resistance training in particular may spare the fat-free mass of the body somewhat compared with diet-based weight reduction. This could be explained by the preservation of glycogen and water in the body.
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