From the article: Encouragingly, the associations between exercise and reduced cancer risks held true even when the researchers factored in body mass. People who were overweight or obese but exercised had a much lower risk of developing most cancers than overweight people who did not move much.
This is directly related to a comment I posted on another article two days ago[0].
This may seem more surprising than it actually is, because by "overweight" and "obese" they are referring to BMI categories, according to the abstract. The overweight BMI category contains people who range from healthy, lean and muscular (think muscular gym goer) to people who have little muscle mass and high body fat percentage (think large beer belly). The fact that you can decrease cancer risk by gaining muscle (usually from increased exercise, precisely the thing being studied) and losing fat while maintaining the same physical mass and thus the same BMI, is not shocking.
Once you control for body fat, having additional muscle mass (thus higher BMI) probably decreases all-cause mortality.[1]
Unfortunately, I don't think this has much bearing on azdle's questions, since people can be fit for many reasons, either by intent or by necessity.
