This story is over 5 years old.

Gut Bacteria Could Be Making Kids Fat

We're still learning about the relationship between the microbiome, antibiotics, and obesity in kids.
What's living inside kid's tummies can help explain why so many kids are becoming obese. Image: Another Sergio/Flickr

When it comes to childhood obesity, we tend to focus a lot on processed food and lack of physical activity. But those aren't the only factors contributing to the epidemic, which affects close to 1 in 5 American kids.

A study published Tuesday shows how the trillions of bacteria that already live in children's guts also impact their risk of obesity. And this understanding may pave the way to new, and better, treatments for obesity.


By studying the gut flora of 84 children and teens—from normal weight to severely obese—researchers were able to determine that the composition of microbes in the gut flora of obese children and adolescents share a lot of similarities. Eight distinct group of microbes were associated with higher body weight, and these groups were less often found in the gut flora of leaner kids, according to the study published in the Journal of Clinical Endocrinology & Metabolism.

These differences in microbiome populations—the term for the unique blend of bacteria that live in and on every human body—mean that obese kids and teens more often have bacteria that are better at fermenting carbohydrates in the stomach, which produces higher levels of short-chain fatty acids (the term for a number of acids produced in the colon when food breaks down).

"Once short-chain fatty acids are produced, either they get expelled through feces, or most of them get absorbed," said Dr. Nicola Santoro, a Yale endocrinology research scientist and co-author of the paper.

Santoro said the researchers believe the short chain fatty acids are being absorbed in the liver and converted to fat, which would explain part of the reason why obese kids might be predisposed to put on weight.

Read More: Scientists Are Now Trying Fecal Transplants on Kids

These findings are similar to those of studies looking at the gut flora of obese adults. It's part of a slow piecing together of a puzzle that explains what role the microbiome plays in our body fat composition, and how we might be able to influence changes.


"Studies have consistently reported an association between antibiotics and gut flora and we know the microbiome plays a role in the development of metabolism and immunity," Annemarie Hirsch, a researcher at the Geisinger Center for Health Research who has authored studies on the impact of antibiotics on the development of the microbiome. "It's the connection between antibiotics to microbiome to obesity that's somewhat still a black box."

Though the microbiome in adults is more or less static—antibiotics can knock out a lot of the microbes, they will repopulate—Hirsch's research has shown that the gut flora of babies is still developing, and the overuse of antibiotics at an early age can change the composition. That overuse is also associated with a higher risk of obesity and food allergies.

Both Hirsch and Santoro said there's still a lot of work to be done and there are a lot of factors that impact risk of obesity: most obviously, diet and amount of physical exercise. But as we learn more about the role the gut flora plays, we might be able to design more strategic treatments for kids and adults who are already obese—or prevent it for those who aren't. These could include things like probiotics, or even fecal transplants, where the fecal matter of a healthy person is introduced into the bowel of another person to repopulate the gut flora with different microbes.

"That's the million dollar question," Santoro said. "If you look at animal studies, fecal transplants work perfectly in mice [for treating obesity.] The issue is: can we do this in humans? Does it work? For obesity, we don't know yet."

Get six of our favorite Motherboard stories every day by signing up for our newsletter.