Neither self-contradictory nor absurd, the “Obesity Paradox” isn’t really paradoxical at all.
Unless you’re talking about infinite hotels or cause following effect in a one-way timeline, I’m not keen on the use of the term “paradoxical.” When it’s applied to scientific conversations — at least in the popular media — it seems to make people think scientists don’t know what they’re talking about, when really it’s usually quite far from the case.
So this week, when an article from Quartz crossed my feed, entitled “Scientists now think that being overweight can protect your health,” it irked me when I found it couched in terms of “The Obesity Paradox.” The so-called “paradox” goes a little something like this:
“Around a dozen years ago, researchers noticed that some patients with chronic conditions such as heart disease fared better than others. […] researchers were baffled. Because the factor that seemed to be protecting these patients was fat: They were all overweight or mildly obese.”
This is to say: with some conditions, it looks like you live a little longer if you have a little more weight on you. The list includes things that are sometimes caused by having too much weight on you, like type II diabetes and heart disease. The idea is that this is paradoxical because being overweight is bad for you. And things that are bad for you are never also good for you… oh wait.
So in a feature in Nature News a couple of years ago (which seems to be mostly where the author of the Quartz piece is getting her info), Virginia Hughes gets into the history of the debate — because if nothing else it is certainly that. According to both the Quartz piece and the Nature News one, the person whose work kicked off the debate was Katherine Flegal of the CDC. She did a massive meta-analysis which concluded that slightly overweight (BMI) people had lower all-cause mortality than healthy weight (BMI) people. Others, for example Walter Willett of Harvard, think it can be chalked up to poor statistical analysis.
The options for explanation, at present, are legion.
There might not be any protective effect to being a little overweight, and we just haven’t controlled properly for confounding factors. Stefan Anker at Charité Medical University is quoted in Hughes article as saying it might have to do with the age at which your weight is medically relevant: “If you are young and healthy, then obesity, which causes problems in 15 or 20 years, is relevant,” he says. With age, though, the balance may tip in favour of extra weight.
Mercedes Carnethon at Northwestern University did a study on type II diabetes sufferers and found that those who developed it with a healthy weight had double the risk of dying over a given period of those who developed it while overweight, which she says “is probably driven by a subset of people who are thin yet ‘metabolically obese’: they have high levels of insulin and triglycerides in their blood, which puts them at a higher risk for developing diabetes and heart disease.”
It might also be that BMI is just a terrible, terrible indicator of health, especially at the lower “overweight” weights. We know — even Flegal’s study agrees — that very overweight people have higher mortality rates. It’s undisputed that they have higher rates of many diseases and that a great deal of excess weight creates medical complications in people already ill. It is never going to be good for you to be very obese. It isn’t, however, very clear at all that being slightly over your prescribed BMI (which is what they’re talking about when they say “overweight” vs. “obese” vs. “morbidly obese“) is unhealthy enough to make a difference in your health outcomes, especially when there are so many other factors, like exercise, diet, stress, genetics, and more.
And, yes, it might actually be that a little bit of extra weight, especially when you’re ill, has a protective effect. We don’t know. But if there were a protective effect, there’d be little paradoxical about it. A great many things in humans are okay in small amounts and terrible in large amounts. Alcohol seems to work this way. Free radicals — those things antioxidants are supposed to protect you from — are useful and necessary in limited doses. UV radiation can be good, too — but will probably also give you cancer. It wouldn’t be paradoxical at all for being mildly overweight to also be good for you and bad for you at the same time in different ways. It’d be pretty much par for the course in terms of how the human body works as a complex system.
As I say, the jury’s still out on this one. But let’s cool it with the “paradox” talk, okay? It’s not impossible, or even surprising, for the dose to make the poison, or for complex conditions to result in complex outcomes.
Richard Ford Burley is a writer and doctoral candidate at Boston College, as well as an editor at Ledger, the first academic journal devoted to Bitcoin and other cryptocurrencies. In his spare time he writes about science, skepticism, feminism, and techno-futurism here at This Week In Tomorrow.