Do Antibiotics Cause Obesity?

It seems there are no shortage of factors contributing to the growing obesity epidemic (recently declared a pandemic by the World Health Organization). But Mother Jones presents research that purports to have found the most unusual culprit thus far: the use of antibiotics, which has similarly been on the rise. First, consider these two maps:

As you can see, there’s a pretty strong correlation between antibiotic use and obesity rates. But that immediately leads to the question of whether this relationship reflects causation. As the article notes:

When we mashed up the data behind these maps, we confirmed the strong correlation between obesity and antibiotic prescription rates (we got an r of 0.74, for the statistically inclined). We also found a correlation between the states’ median household incomes and antibiotic prescription rates: States with below-average median incomes tend to have higher antibiotic prescription rates. This makes sense, considering that high obesity rates correlate with low income levels. (You can see the data sets for antibiotic prescription rate, obesity, and median household income level here.)

Hicks and her team can’t yet explain the connection between obesity and high rates of antibiotic prescription. “There might be reasons that more obese people need antibiotics,” she says. “But it also could be that antibiotic use is leading to obesity.”

Indeed, both factors could be due to a shared cause, such as socioeconomic status: most of these states have high rates of poverty, and poorer Americans tend to be more susceptible to both illness and obesity (due to low access to medical care and nutritional food).

However, it seems as if antibiotics play a direct  role in obesity.

Indeed, a growing body of evidence suggests that antibiotics might be linked to weight gain. A 2012 New York University study found that antibiotic use in the first six months of life was linked with obesity later on. Another 2012 NYU study found that mice given antibiotics gained more weight than their drug-free counterparts. As my colleague Tom Philpott has noted repeatedly, livestock operations routinely dose animals with low levels of antibiotics to promote growth.

No one knows exactly how antibiotics help animals (and possibly humans) pack on the pounds, but there are some theories. One is that antibiotics change the composition of the microbiome, the community of microorganisms in your body that scientists are just beginning to understand. (For a more in-depth look at the connection between bacteria and weight loss, read Moises Velasquez-Manoff’s piece on the topic.)

Like any good study, there’s a caveat to keep in mind:

Hicks says that more research is needed on the potential connection between antibiotics and obesity. But there are other reasons for doctors to change the way they prescribe antibiotics. As I noted a few weeks back, a recent study in JAMA Internal Medicine found that doctors commonly prescribe antibiotics for symptoms such as sore throat and bronchitis—which don’t usually require the drugs. Considering that bacteria are already evolving to withstand many antibiotics, it’s probably time to figure out how to use them more prudently.

One thing seems certain — the causes of obesity go far beyond overeating and being too sedentary. There seem to be many more factors at work, even some unlikely ones.

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