The fact that obesity is caused by a simply energy imbalance that leads to fat accumulation is ingrained into mainstream scientific and medical thinking. This highly over-simplified hypothesis is obstructive because it prevents open-minded debate and unbiased research from occurring, in order to try to find effective solutions to the rise in the number of cases of obesity. Exercise and calorie restriction appears to show no ability to cause successful long-term weight loss in obese individuals, suggesting that energy imbalance is not the most important factor in the development of excess adiposity. There is an association between exercise and body weight, but the cause and effect is not able to be ascribed without careful scientific investigation. Unfortunately, because the of the reliance on a priori knowledge regarding obesity, many studies contain inherent bias and as such care must be taken when interpreting results.
For example the conclusion of a 5 year prospective study1 investigating abdominal obesity stated that ‘higher levels of physical activity reduces abdominal obesity independent of baseline changes in body weight and is thus is a useful strategy in preventing chronic disease and premature deaths’. The results showed that physical activity was a significant predictor of a lower waist circumference in 84 511 men and 203 987 women. Of the subjects in the study, 5.1% of men and 4.2% of women progressed to obesity by the end of the study period, and the authors claim a 7% (men) and 10% (women) odds reduction on this occurring as physical activity was raised by one category. However, the study was a prospective cohort study that was investigating associations between abdominal obesity and physical activity levels, and therefore did not have any scientific validity in ascribing the cause and effect of the association.
Interestingly, in younger individuals (<50y), the association between physical activity and changes body weight was driven mainly by normal-weight individuals suggesting that exercise had no effect on the weight of obese individuals. In addition, physical activity was not associated with changes in the body weight in older men or women, although for women it did predict reduced weight gain. In this study therefore, the baseline levels of physical activity were not associated with a change in body weight, but only with changes to the waist circumference (abdominal obesity). As the authors state in the discussion, the association between physical activity and gain in body weight may be restricted to individuals <50y of age and those of normal weight at baseline, which raises serious questions about the validity of the hypothesis that exercise causes weight loss due to changes in energy balance.
While physical activity may cause reductions is abdominal body fat, it could also be the case that those with lower abdominal adiposity are more able to exercise due to lighter bodyweights, reversing the cause and effects. Equally, a third variable may control both abdominal obesity and physical activity. Testosterone for example is know to reduce abdominal body fat, increase energy reserves for exercise and improves the desire to perform physical activity. The fact that clinical trials show that exercise is ineffective at causing long-term weight loss along with data from epidemiology that shows associations between exercise and body fat are only present in some sub-groups, should raise questions about the validity of the energy balance hypothesis. The complexity of the statistics used, along with the division of the criteria into smaller sub-groupings in order to find significance, speaks volumes about the true nature of the data in this paper.
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