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We get it. We’re fat. Americans are fat. Europeans are fat. And the rest of the globe is quickly catching up. And, yes, excess weight is very, very bad. Gaining too much weight boosts your risk of cancer, heart disease, and, well, 17 other terrible things that we’ve written about before.

So, do our chubby thighs and seems-like-we’ll-never-shed-it baby weight always spell disaster? Is there any silver lining at all? Maybe. Here are five surprising things you may not know about weight—and why a few extra pounds aren’t always as bad as you think.

MYTH No. 1: A high BMI means you need to shed pounds.

FACT: Body mass index, or BMI, is a good starting to point to determine if you’re in shape because it is a simple number that takes into account both height and weight. (You can easily check your BMI using a calculator). But it isn’t perfect—far from it.

BMI does not take into account physical fitness or bone structure, and it doesn’t differentiate between weight gained at a muscle-building camp or weight gained at McDonald’s.

So if you’re packing a lot of muscle—say, if you’re a bodybuilding male—you may end up with a BMI in the obese range. (For example, at the peak of his bodybuilding career, Arnold Schwarzenegger had a BMI of 33, which is considered obese.)

Keri Gans, a registered dietitian and American Dietetic Association spokesperson, measures her clients’ BMI during a consultation, but takes the number with a grain of salt. “The key is muscle,” she says. “A bodybuilder might have a BMI that’s almost obese, when he’s just really, really built with a lot of muscle.”

Next page: MYTH No. 2: Extra pounds are always bad news.