Does exercise reduce obesity? evidence from Australia

The International Obesity Taskforce calls obesity one of the most important medical and public health problems of our time. An estimated 1 billion people around the world are over weight, of whom around 300 million are clinically obese. Estimates suggest that obesity levels will continue to rise in the early 21st century - with severe health consequences in the absence of quick and directed intervention. Leaving genetics aside, obesity is essentially due to an imbalance between caloric intake and expenditures i.e, too high caloric intake and too low caloric expenditure. A large part of the economic research on obesity has focused on factors that lead to this imbalance. In this paper we examine the relationship between obesity (as measured by BMI) and the duration of exercise. Single equation estimates show that exercise duration has a negative and statistically significant effect on the probability of being overweight or obese. However when we take into account the potential endogeneity of exercise duration in the BMI regressions (arising from a standard problem of reverse causation), we no longer find a negative relationship between exercise duration and BMI. There is either no effect or the effect is actually positive indicating that the results are essentially driven by individuals who are and who perceive themselves to be overweight and obese conducting more exercise.