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Smoking marijuana is notorious for bringing on the munchies, but a new study has found that contrary to what you might think, pot smokers are skinnier than their non-smoking peers.

Rates of obesity are lower by roughly a third in people who smoke pot at least three times a week, compared with those who don't use marijuana at all, reports Time's Healthland blog.

Researchers looked at the results of two large national surveys of Americans, covering about 52,000 people. In one, 22 per cent of those who did not smoke marijuana were obese, compared with just 14 per cent of the regular marijuana smokers. In the second, 25 per cent of nonsmokers were obese, compared with 17 per cent of regular cannabis users, reports the blog.

The study is published in the American Journal of Epidemiology.

Yes, we know correlation doesn't equal causation, or, as writer Maia Szalavitz puts it, "...the correlation between weed and weight doesn't mean that marijuana smoking actually causes weight loss."

Some suggested mediators at work could include religious faith, since highly religious people are less likely to take drugs, but more likely to be obese.

"So, some of the obese people in the national surveys may be religious folk, who might otherwise be heavy marijuana smokers, but are eating too much instead. That could make it look like marijuana is slimming," she writes.

One nagging question, though, is why marijuana smokers didn't get fatter by taking a drug that can clearly stimulate appetite – one of the major uses of medicinal marijuana.

One factor may be tolerance: many of marijuana's effects are reduced in frequent users, as the body adjusts to it, she writes.

"Another may be substitution — the smokers could be seeking comfort by smoking more marijuana, rather than eating more. Or, perhaps other ingredients in cannabis like cannabidiol (CBD) could reduce the appetite-increasing effects of THC in the same way that they reduce its paranoia-inducing properties."

Bottom line: Here's hoping this study doesn't show up as the basis for the next diet fad.

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