The efficacy of exercise in the treatment of established obesity
Objective. The objective of this narrative review was to examine cross-sectional empirical data on the efficacy of adequate doses of daily physical activity in the treatment of established obesity. Methods. Information obtained from Ovid/Medline and Google Scholar through to June 2019 was supplemented by a search of the author's extensive personal files. Results. Randomized controlled trials have shown a small but consistent effect of exercise programmes in reducing the body mass and body fat content of the obese. Some non-randomized trials have adopted larger volumes of exercise (2-4 MJ/day), and weight losses of 10 kg or more have then been observed. Dieting has generally given a greater weight loss than exercise, but some of this apparent advantage has reflected a greater loss of lean tissue. Changes in lean tissue mass have under-estimated the beneficial impact of exercise programmes by 2-3 kg, while exaggerating the benefits of dieting by 2-3 kg. Fat loss seems to occur a little more easily in men than in women, and it is also easier to mobilize abdominal fat than subcutaneous fat. The minimal dose of physical activity recommended by public health authorities seems insufficient to deal with established obesity; adults need 150-250 minutes of exercise per week, incurring an additional weekly energy expenditure of 4.8-8.0 MJ, and children may require even larger doses of activity to counter obesity. High intensity programmes save time and may be somewhat more effective for any given energy expenditure than longer periods of moderate activity. A combination of dietary restraint and heavy exercise can cause an 8.5 kg loss of fat over 8 weeks. However, long-term adherence to high intensity programmes is more problematic. It may be helpful to split a single session of aerobic activity into several shorter segments. Causes of a limited response to exercise include an insufficient exercise prescription, poor programme adherence, and a compensatory increase of food intake, compounded by reductions in resting metabolic rate, spontaneous leisure activity and NEAT. Meta-analyses have typically shown weight and fat losses of around 10 kg with 3 months of combined dieting and exercise, but in a few instances much greater weight losses have been reported. Moderate exercise sessions have sometimes added little to dieting alone, but it remains unclear whether more rigorous physical activity programmes might lead to a greater fat loss. Exercise is helpful in preserving lean tissue; it also confers many ancillary health benefits such as enhanced cardio-respiratory fitness, and it may limit the regain of weight after the completion of formal treatment. Resistance exercise is particularly helpful in conserving lean tissue. In a long-term perspective, lifestyle activities may more effective than a formal exercise programme. Much of initial weight loss is often regained within a year, but continued exercise and dieting conserve at least 3 kg of the initial weight reduction. Conclusions. Moderate exercise alone has less effect upon obesity than rigorous dieting, but benefits are larger if the exercise dose can be increased. Exercise helps to conserve lean tissue, and plays an important role in weight maintenance. The challenges to health professionals are to develop safe methods of reaching an effective dose of exercise in those who are obese, and in sustaining the enthusiasm of such individuals for an active lifestyle once initial weight goals have been attained.
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