Antibiotics May Be Making You Fat

By wiping out gut bacteria, researchers found that antibiotics could make mice fat

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Om nom nom Crwr / Milo Tobin

There are loads of reasons doctors shouldn’t over prescribe antibiotics. Bacteria become resistant to the drugs, people spend money when they don’t need to, patients can experience horrible side effects, and they’re often not making people any better. But if fiscal responsibility and the threat of a deadly complication is not enough to deter the over-dependence on antibiotics, then maybe the recent research by of Ilseung Cho will do the trick. Though working with mice, not people, Cho and his team found that persistent low doses of antibiotics made them fat. Ed Yong at Not Exactly Rocket Science describes the research:

Cho exposed young mice to a range of different antibiotics including penicillin, vancomycin, the two together, or chlortetracycline, all at levels that the US Food and Drug Administration approves for use in agriculture. After 7 weeks, the treated mice were no heavier than those that didn’t drink any drugs, but they had more body fat – around 23 percent, compared to a typical 20 percent.

The researchers’ thinking is that the antibiotics nuked the bacteria living in the mice’s intestines—their so-called “microbiome”—bacteria which help break down and use the nutrients in food. With their guts cleared out, different types of microscopic organisms were able to take hold. Comparing mice that used antibiotics to those that didn’t, says Yong, the antibiotic-treated mice,

…had the same numbers of microbes as the normal mice, but they were heavier in bacteria from the Firmicutes group, and poorer in those from Bacteroidetes. That’s a familiar pattern to anyone interested in gut bacteria: many studies have found that the balance between these two bacterial groups sways to the Firmicutes’ favour in obese individuals. It’s the same for both mice and humans.

“This scenario is, for now, a hypothesis,” cautions Brandon Keim at Wired.

Antibiotics are regularly doled out by doctors to patients who demand them, not who need them. From Time:

Most upper respiratory infections are caused by viruses, and will clear up on their own in a few days. Yet about half of the 100 million prescriptions written for antibiotics each year are for respiratory ailments that aren’t going to be helped by a drug.

Prescribing an antibiotic for a viral infection is not only wasteful, it can hurt the patient. More than 140,000 people, many of them young children, land in the emergency room each year with a serious reaction to an antibiotic. Nearly 9,000 of those patients have to be hospitalized.

Of course, antibiotics have done a lot of good too — they’ve neutered diseases that once ravaged through the population. But as will all things, moderation and appropriate use are always in order.

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