Science Scope

Could antibiotics be causing the obesity epidemic?

Could antibiotics be causing the obesity epidemic?

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Just as animals fed a steady stream of antibiotics gain weight, two studies show a connection between exposure to antibiotics and an increase in body mass.

Yikes. The very medicines we turn to for a cure may be causing us harm.

Two new studies show that antibiotics could be harming the bacteria in our guts, causing us to pack on the pounds. And the hypothesis isn't so far-fetched, considering that the cattle and pigs we raise as meat are fed a steady stream of antibiotics that have been shown to help them gain weight.

In the first study, which was conducted in mice, exposure to antibiotics disrupted the mice's internal microbe communities, resulting in changes in the way the mice's bodies could process food and regulate metabolism.

The other study showed that the more exposure children had to antibiotics as infants, the higher their body weights.

“Early life antibiotics are changing the microbiome, and its metabolic capabilities, at a critical time in development,” microbiologist Martin Blaser of New York University, an author of both of the studies, told Wired. “These changes have downstream effects on metabolism, including genes related to energy storage.”

The studies

Blaser is a pioneer in researching the microbiome, the community of bacteria, viruses, fungi, amoebae and yeasts that live and die in and on our bodies, helping out with functions like breaking down food. They are a huge part of the human ecosystem, because the number of microbes on our bodies (about 100 trillion) can outnumber the cells that make us human by ten to one.

The changes in the microbiome have been linked to a number of diseases including cancer, autism and heart disease. Plus, obesity. Blaser wondered if this link had anything to do with the fact that animals in concentrated animal feeding operations (CAFOs, pictured above) are fed a steady stream of antibiotics and that they grow larger and faster than normal.

First study

With NYU microbiologist Ilseung Cho, he fed lab mice low doses of antibiotics, much the way animals in CAFOs would ingest them.

Though the mice didn't gain weight, their body fat increased 15%, no matter what type of antibiotic he fed them. Also, their microbiomes were quite different from mice not fed the antibiotics. Even more surprising is that the mice showed a change in their genes, particularly the genes involved in breaking down carbohydrates and regulating cholesterol.  The results were published in an Aug. 22 Nature paper.

Second study

While mice bodies are admittedly different from human bodies, Blaser also has a study, published in the International Journal of Obesity, of the effect of antibiotics in 11,000 British children.

That study showed that children who were exposed to antibiotics before the age of six months had higher body mass years later.

What's next

The two studies don't necessarily prove that the effect seen in mice and the effect seen in humans are the same, given that the human exposure was a one-time exposure, rather than a steady low dose as in the experiment with mice.

Blaser will next look at how a single dose of antibiotics early in life affects the body weights of mice. He's also going to study the effects in human bodies of the kind of low doses of antibiotics we take in from eating meat and dairy from animals fed antibiotics.

Related on SmartPlanet:

via: Wired

photos: Top: Concentrated Animal Feeding Operation (CAFO) (EPA via Wikipedia); Bottom: Two mice, top one not fed antibiotics has less fat (shown in yellow); mouse at bottom, fed a regular dosage of antibiotics, a has thicker layer of fat. (Cho, et al., Nature)

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Laura Shin

Features Editor

Laura Shin has been published in The New York Times, The Wall Street Journal and The Los Angeles Times, and is currently a contributor at Forbes. Previously, she worked at Newsweek, the New York Times, Wall Street Journal and LearnVest. She holds degrees from Stanford University and Columbia University's Graduate School of Journalism. Follow her on Twitter. Disclosure