Diet, physical activity and cancer risk.

There is a clear and consistent association between overweight and risk of hormone-related cancers, large bowel cancer and cancer at some other sites. Overweight is the consequence of an excess of energy intake over expenditure, but there is little evidence of an association between high energy intake and cancer risk in humans at any site other than the endometrium. This may be because of the difficulties in measuring total energy intake in the tens of thousands of individuals used in large prospective epidemiological studies. In contrast, despite the difficulties in measuring physical activity in the large numbers of persons needed in epidemiology, there is a growing body of evidence that a high level of recreational physical activity is protective against cancer at all sites associated with overweight.