Study Says Obesity Could Be Infectious; Here’s Why You Shouldn’t Worry

We’ve all heard borderline fat-shaming advice about how hanging out with your fat friends could make you fat, too, because a) all fat people eat badly, and b) if you spend enough time around them, you’ll start eating that way yourself. But a new study is taking headlines to a new level, claiming that obesity could be infectious—like, “don’t breathe on me or I’ll get fat,” infectious. But before you start freaking out about catching the fat bug, we’re here to assure you: In all likelihood, you cannot catch obesity from your friends.

For the study, which was published in Nature, researchers engineered mice to have a particular immunodeficiency which leads to fatty liver disease, and got fatter when fed a Western-style diet. The surprising part was when they put healthy mice in the same cage as the immuno-deficient ones; the healthy ones got fatter and developed liver disease, too. Researchers concluded that gut bacteria imbalance was to blame. According to Fox News:

Because the mice had their immune systems disturbed, the bacteria in their guts got “out of wack,” said study researcher Richard Flavell, a professor of immunobiology at Yale School of Medicine. We normally live in symbiosis with the bacteria in our guts, but in the study, the number of “bad,” disease-associated bacteria increased 1,000-fold in mice with immune problems, Flavell said.

Fox, like many other media outlets, is focusing on Flavell’s best direct quote:

We could make a mouse fatter just by putting it in the same cage as the other mouse.

But they’re not focusing on the major footnote: That it’s unlikely this could happen in humans, because we don’t eat each other’s poop. Mice do. Flavell told Fox that several more studies would be needed to determine whether the same thing happens in humans, but that the likely reason for such efficient transfer of gut bacteria between mice is the fact that they chow on each other’s feces.

But mice making each other fat by eating each others’ poop doesn’t make for such sensational headlines, so most media outlets are just hyping up the possibility that fat could be contagious. (Because that’s sure to make people take responsibility for their own health and get over damaging fat stigmas in our society.)

Instead of getting freaked out about contracting fat from other people, let’s all just be thankful that we don’t eat each other’s poop (and then go pop a probiotic, because this article was a good reminder that those are important, too).