Years ago, I was teaching a college course called The Psychology of Eating and Body Image, and I ended up becoming dear friends with one of my students, a woman named Anna. She introduced me to the obesity paradox. It claims that obesity is not always bad for your health and, in some cases, can actually protect your health. My friend herself seemed to be evidence of this paradox: she was living with extreme obesity but had no markers of ill health.

Is there a nugget of truth in this paradox? Or is it always bad for your health to be obese? Turns out the so-called “obesity paradox” is an artifact of three methodological research flaws, and when those biases are accounted for, the obesity paradox vanishes entirely. When you account for the misdiagnoses inherent in using BMI as the measure of obesity when you fail to account for weight loss due to illness, and when you bake in something called collider stratification bias, the “obesity paradox” results. But it’s just a mirage. Alas, yes, it really is extremely unhealthy to be overweight or obese. In fact, a recent Rand study showed that obesity is worse for chronic health conditions and healthcare spending than poverty, smoking, or heavy drinking. And obesity confers a 91% increased risk of death. Every bit of excess weight we carry makes our health worse. The data are clear—there is no paradox. It’s unhealthy to be overweight.