The mainstream medical viewpoint on weight gain is that it is caused by a positive energy balance, as a direct result of a low energy expenditure coupled to a high energy intake. However, despite the persistence of this view, research has consistently shown that increasing energy expenditure in order to create a negative energy balance is not an effective method of reducing weight, long-term. Further, evidence is accumulating that it is not energy intake that is the main contributory factor in weight gain, instead it appears that certain foods are able to cause metabolic dysfunction, that results in insulin resistance, central adiposity and ultimately leads to the metabolic syndrome and obesity. Poor quality food may therefore cause abnormalities in the delicate hormonal control system that modifies satiety as well as altering the compartmentalisation of macronutrients through detrimental changes to insulin sensitivity.
Associations between weight gain and reduced physical activity in modern living are difficult to quantify because as levels of physical labour have declined, eating habits have also changed. It is often assumed that higher levels of physical activity in developing countries are responsible for the reduced incidence of obesity, but this may also be due to the avoidance of problem foods that cause metabolic dysfunction. In fact, weight gain tends to be absent from societies that do not have access to highly processed foods, irrespective of their physical activity levels. Therefore, longitudinal studies that indicate how activity levels may cause changes in weight over time are useful to researchers. For example, research published in the American Journal of Clinical Nutrition in 20091 investigated the relationship between variations in energy expenditure at baseline and weigh changes over time in Nigerian and African American Women.
In this prospective study, researchers measured the total energy expenditure and resting energy expenditure of 149 women from rural Nigeria and 172 African women from the Untitled States. This was achieved using gas expiratory exchange and doubly labelled water. Physical activity levels and anthropometric measurements were taken at baseline, and subsequently weight changes were monitored for three years. The mean body mass index was 23 and 31 kg/m2 and the prevalence of obesity was 7 and 50% in the Nigerian women and African American women, respectively. However, no differences were found in the mean activity energy expenditure of the two groups, suggesting that physical activity levels were not the cause of the differences in body weight. In addition, activity levels of individual subjects at baseline did not predict the subsequent weight gain over the three years of the study.
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