Do These Microbes Make Me Look Fat?

Mice that were implanted with the gut bacteria of obese humans gained more weight than mice that got microbes from thin people. Katherine Harmon reports.

Illustration of a Bohr atom model spinning around the words Science Quickly with various science and medicine related icons around the text

Join Our Community of Science Lovers!

Our bodies are home to trillions of other organisms that influence our health—and probably our weight.

Researchers found that mice given gut microbes from obese humans became fatter than those that got microbes carried by slim folks. When the husky and lean mice shared microbes with each other, the bigger ones picked up some of the beneficial gut flora—and had improved metabolisms.

But this shift only occurred if the mice were on a high-fiber, low-saturated fat diet. If they were on a junk food diet, no improvement. The findings are in the journal Science. [Vanessa K. Ridaura et al., Gut Microbiota from Twins Discordant for Obesity Modulate Metabolism in Mice]


On supporting science journalism

If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.


It’s not clear how humans might remodel our microbial communities to change health or weight class. The mice in the study were raised in germ-free environments and had no native microbiomes of their own.

In people, so-called fecal transplants have been reserved for more severe conditions than a bulging belly. And probiotic products, such as yogurt, are minimally effective. But flat or fat, what your belly looks like on the outside might have a lot to do with what's on the inside.

—Katherine Harmon

[The above text is a transcript of this podcast.]

It’s Time to Stand Up for Science

If you enjoyed this article, I’d like to ask for your support. Scientific American has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in that two-century history.

I’ve been a Scientific American subscriber since I was 12 years old, and it helped shape the way I look at the world. SciAm always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. I hope it does that for you, too.

If you subscribe to Scientific American, you help ensure that our coverage is centered on meaningful research and discovery; that we have the resources to report on the decisions that threaten labs across the U.S.; and that we support both budding and working scientists at a time when the value of science itself too often goes unrecognized.

In return, you get essential news, captivating podcasts, brilliant infographics, can't-miss newsletters, must-watch videos, challenging games, and the science world's best writing and reporting. You can even gift someone a subscription.

There has never been a more important time for us to stand up and show why science matters. I hope you’ll support us in that mission.

Thank you,

David M. Ewalt, Editor in Chief, Scientific American

Subscribe