Obesity and lack of physical exercise are on the ascendant—not only in their own right¹ but as targets of health policy. Recent discussions at the G8 summit and the “Make Poverty History” campaign have highlighted the growing inequalities of affluence worldwide and have made us feel embarrassed by our glutton and sloth. The government is now trying to tackle the problem at its roots, focusing on “healthy” school meals and promoting exercise with the hope that fit and lean children will grow up to be healthier adults.² The decision to host the 2012 Olympics in London will be a further fillip for this policy.

There are now multiple studies which demonstrate an association between obesity, exercise, and colorectal cancer incidence and mortality.^3–6 It has been estimated that overweight and obesity could account for 14% of male and 20% of female cancer deaths in the USA.³ But getting a clear message from these studies can be difficult. Some papers report different associations for men versus women or for colon versus rectal cancer or for different measurements of overweight/obesity. It is reasonable to suppose that these types of risk factors might affect both sexes and parts of the colorectum in similar ways, although perhaps not to the same degree. So, do conflicting results reflect a true lack of association or are we missing the point by measuring the wrong parameters? Although the end points, such as cancer incidence and mortality, are simple to record accurately, measuring obesity and physical activity can be very difficult. There are no surrogate markers that can be easily measured in a blood test, for example. Weight, height, body mass index (BMI), waist circumference, …