SAGAL: This is amazing. Scientists have determined, the data is clear, that patients with some chronic conditions - many in fact - fare better, live longer if they're overweight. They do better with heart disease, pneumonia, cancer and if they're handed a large bunch of balloons, they are far less likely to float away.
SAGAL: Nobody knows how this could be true because all of the things that people do to get fat - you know, lack of exercise, too much fatty foods, too much sugar - all that is still bad for you. But actually being fat is good for you. This phenomenon is called the obesity paradox, which is also what happens when you go back in time and eat your own father.
Underneath the dumb fat jokes there's a puzzle that many people consider a serious conundrum. We are told that weight gain is caused by unhealthy behaviors, and therefore we expect people who are overweight to be less healthy and die sooner than their more slender peers. However, as has been known for a long time, the medical evidence doesn't back that up. Individuals ranked as overweight have better medical outcomes, including longer lives, than individuals ranked as having normal weight. We seem to have a situation where individually unhealthy behaviors are leading to an increase in health, which would appear to be a paradox. Especially since individual lifestyle choices is the only model we've been given to manage our own well being.
This paradox is actually classic question-begging. The real question we should be answering is: how is body weight related to heath? Like the study referenced in the story above, we could look at a wide range of disease and health outcomes and see how they correlate with different behaviors and various measures of body type, weight, and shape. The outcome could then be used as a guide to behaviors that would result in better health outcomes, at least in general terms. We have to do that research first, and then define what we mean by "overweight" -- a weight that's higher than is healthy -- as a result of that.
Instead this paradox puts the cart before the horse and assumes the answer. A BMI over 25 is unhealthy, it says, so why aren't these stupid fat people dying already? It turns out that if you actually do the research, BMI is a not a proxy for health at all. In fact it's terrible as a predictor of health outcomes. The intuition is that people who are overweight got that way because of unhealthy behaviors -- not enough exercise, and foods with too much fat and sugar -- and also that people who have normal weight got that way because of the reverse, healthy behaviors. This is a very strong claim with not much evidence. Note that this is not the same as the conventional wisdom that if you eat more or exercise less you'll experience weight gain. That's not generally true either, but it least it has some basis in reality. The converse claim, that you can determine people's behavior and diet by measuring their height and weight is frankly absurd.
Unfortunately the empirical research won't change people's mind. This is really about a morality play, and an ugly one at that. Thin and muscular bodies belong to virtuous people, while fat and flabby bodies are the result of vice and belong to people with poor morals. Moral scolds tell fat people that they must lose weight, or if not to stay out of public spaces. Fat hatred is rife with elliminationist rhetoric so vile that if it was directed at a ethnic group it would be a hate crime. This so-called paradox exists because people want to believe that fat people are to be shunned for their lack of morals and deserve to die sooner.