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Fat chance for physical activity

Professor Bruce Neal comments on a new study showing the rise in physical activity is not combating the obesity epidemic in the United States.

The enormous burden of ill health caused by overweight and obesity is well understood, particularly in developed countries like the United States, which have seen massive increases in prevalence over the last few decades.

At its most basic level, obesity is easily understood as a problem of energy balance - if energy intake from food exceeds energy expenditure from physical activity, weight gain ensues.

Likewise, it follows that if energy intake can be reduced or physical activity increased, weight loss should follow.

A new study published today in Population Health Metrics provides important new insight into where the United States should focus its efforts over the next few years. The key observation is the apparently paradoxical association between changes in physical activity and obesity–average levels of physical activity in the United States appear to have risen, but so too have obesity rates.

The most likely explanation for this finding is that the rise in average physical activity levels has been outstripped by the excess of energy provided by the food supply.

So, while physical activity will benefit the health of the population even if it is not accompanied by weight loss, physical activity will not address most of the burden of ill health caused by obesity. That is going to require a new focus on the root cause of the problem – the American diet.