Can regular physical activity prevent obesity?

Part 2: Empirical cross-sectional evidence of efficacy.

Abstract

Objective. The objective of this narrative review is to examine cross-sectional empirical data suggesting the efficacy of adequate daily physical activity in the prevention of obesity. Methods. Information obtained from Ovid/Medline and Google Scholar through to March 2019 was supplemented by a search of the author's extensive personal files. Results. Average skin-fold readings are often as low as 5 mm, in male elite long-distance competitors who spend many hours per week in training, and values for female endurance competitors are also often only a half of those found in the general female population. Physical education students (particularly men) are somewhat thinner than their peers in other faculties, but this advantage is attenuated in averaged data because a proportion of PE students have a lesser commitment to an active lifestyle, and also some students in other faculties engage in physically demanding inter-collegiate sports. Early occupational studies showed low body fat levels in physically active occupations, and a similar difference can still be observed in elite military groups where high daily energy expenditures are required. Amish and Old-order Mennonite families who eschew modern mechanical devices have very high levels of daily physical activity, and this is reflected in their correspondingly low levels of body fat. Similar findings have been reported for Inuit who still follow a hunter-gatherer lifestyle. Studies validating questionnaires and accelerometers in the general population have show correlations of up to -0.50 between scores on such instruments and estimates of body fat content. Finally, cross-sectional comparisons within circumpolar communities have demonstrated higher levels of aerobic fitness in those populations with the least acculturation to a sedentary "white" lifestyle, and this sub-group of circumpolar residents also has a low body fat content. Conclusions. Conclusions about the impact of vigorous daily physical activity upon body fat content are limited by the possible self-selection of a physically active lifestyle, with the adoption of other favorable health behaviours by active individuals. Nevertheless, all of numerous population comparisons show lower levels of body fat in those igroups who maintain an adequate level of habitual physical activity. In some cases the levels of physical activity adopted have been very high, but there are also examples of populations where a favourable body composition has been associated with the regular performance of volumes of physical activity that are appropriate for average middle-aged adults.