Can regular physical activity prevent obesity? 3: Empirical longitudinal evidence of its efficacy.
Objective. The objective of this narrative review is to examine longitudinal data pointing to the efficacy of adequate daily physical activity in the prevention of obesity. Methods. Information obtained from Ovid/Medline, Pub-Med and Google Scholar through to April 2019 has been supplemented by a search of the author's extensive personal files. Results. Babies that have a high level of spontaneous physical activity generally accumulate less body fat then their peers over the first few years of life. However, there is little evidence of a favourable response to supplementary exercise programmes in pre-school children, perhaps because of practical difficulties in augmenting habitual physical activity in this age group. Summer "obesity camps" for older children usually induce a substantial immediate decrease of both body mass and tissue fat stores, but it is unclear how far this reflects dietary restrictions at the camp rather than an increase of physical activity in this environment. Five of 8 uncontrolled longitudinal studies of children and adolescents with subjective assessments of habitual physical activity found no beneficial changes of body composition in individuals who were physically more active, as opposed to 3 positive reports (one of these seeing benefits in girls only). However, perhaps because more accurate categorization of exercise levels was possible, benefit was demonstrated in 8 of 10 trials of children with objective assessments of habitual physical activity. Fifteen of 26 trials of children and adolescents with group programme assignment also found a better body composition in those assigned to groups that were more physically active, although participants in 9 of thes 15 trials were given not only an increase of physical activity, but also dietary advice and/or a restriction of food intake. Cohort studies in adults have found fairly consistently that regular physical activity reduces obesity or prevents the increase of body fat content usually associated with aging; benefit was seen in 14 of 17 studies of young adults, and 20 of 21 groups of middle-aged and older individuals. The portion of the day allocated to sedentary behaviour has also been associated with the development of obesity in 4 of 6 studies in children, and 10 of 13 trials in adults. Likewise, the transition from physically active hunting and gathering to an "urban" lifestyle has been associated with an accumulation of body fat in arctic Inuit. In children, randomized controlled trials have shown beneficial changes in body composition from interventions only when the intervention has been effective in achieving a substantial increase of daily physical activity. However 27 of 31 controlled studies of adults have demonstrated a reduction of body fat content in response to a variety of exercise initiatives. It is more difficult to assign a vigorous exercise programme to the frail elderly, and in this age group there has as yet been little study of the potential to reduce body fat by an increase in physical activity, although this would confer obvious functional benefit on those with limited muscle strength. Conclusions. Both in children and in adults, the bulk of prospective and controlled trials point to the efficacy of adequate volumes of regular exercise in both the prevention and the control of obesity. But as with initiatives based on rigorous dieting, the challenge to health professionals is to sustain the enthusiasm of clients over a sufficient period for a programme to take effect and to become a part of the individual's normal lifestyle.
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