Losing weight is far more complicated than eating way less and exercising way more, as recently became evident in contestants on The Biggest Loser. Many of those who had success on the show gained their lost weight back (and then some), thanks in part to the destructive effect that rapid weight loss had on their metabolisms.
But what does that mean, exactly? Metabolism is a complicated process that broadly refers to the way your body uses and stores energy from food, and even with this recent buzz around the topic, many still don't quite understand how it works. That's probably why people blame their metabolism no matter how much they weigh. There's no one who challenges them!
Almost no one: there are nutrition and metabolic experts who study this stuff for a living. They offered some of the most common metabolism myths they hear, and set the record straight.
Dieting revs up your metabolism
Exhibit A to dispel this myth: The Biggest Loser. In order to lose weight, you need to burn more calories than you're taking in, but it's important not to completely deprive yourself by cutting too many calories out of your diet. "That can change your metabolism for the worse," warns Dr. Robert Lustig, professor of pediatrics in the division of endocrinology at UCSF and president/co-founder of the nonprofit Institute for Responsible Nutrition.
The key is a hormone called leptin, which tells your brain when you've consumed enough calories. If you're overweight, there's a good chance you have high insulin levels, and insulin blocks leptin, explains Dr. Lustig. Your brain doesn't "see" the leptin, so it thinks you're hungry, causing you to eat more, driving weight gain. "In order to fix your metabolism then, you have to fix the leptin issue," he says. It's not just a matter of cutting your calories, in other words; you have to reset your hormones over time. In fact, calorie restriction is associated with a slower metabolic rate, so extreme diets tend to move your RMR in the other direction. With slower metabolic rates, you'd need to decrease your calorie count even more to continue losing, or even to maintain weight loss. Hence the Biggest Loser conundrum.
Eating late at night screws up your metabolism and makes you gain weight
While there's some evidence that eating more often without increasing your calories can help your cholesterol levels, it hasn't concretely been proven to affect your resting metabolic rate, or RMR. It's more so the number of calories you're eating -- not when you eat them -- that can cause weight gain. "There is little evidence to support the fact that eating after 8pm causes weight gain," says Jennifer McDaniel, RDN, spokesperson for the Academy of Nutrition and Dietetics, and the science backs her up. There's no reason that eating a late meal, on its own, would dramatically alter your metabolism. "However, you may be more likely to snack mindlessly in the evenings while watching television, and calories in these snacks add up quickly, and that can cause weight gain."
Metabolism shuts off at a certain age
Not quite! It's true that as you age, your RMR decreases, but it doesn't just quit on you. Inactivity, change in body composition, and the loss of muscle mass, as well as changes in your hormone levels, all affect your RMR, explains McDaniel. "It decreases by about 1-3% per decade after the age of 30." In the grand scheme of all potential or likely age-related declines, that's hardly much to complain about... especially considering what's going to happen to your knees.
Supplements can change your metabolism
Don't believe everything you read on a label, especially one that isn't regulated by the FDA. "We have a $121 billion nutraceutical industry," says Dr. Lustig, "but none of them are required to show efficacy." That's a nice way of saying that supplement makers don't have to prove that their supplements actually work, which is probably something you should consider before splurging on a bucket of META-BOOSTER XTREME 10,000, or whatever Olympic athletes are getting busted for these days.
The only way to affect your metabolism is by losing or gaining a bunch of weight
Running, biking, and strength training are all beneficial for your overall health, but the benefits go well beyond keeping your heart in good shape and dropping a few pounds. In your body, you have white fat (bad) and brown fat (good) -- exercise seems to turn white fat into brown fat, making it more "metabolically active," which basically means it helps other cells in your body process sugar and energy more efficiently. So even though you may have the same body fat percentage, and even the same weight, working out positively affects your metabolism.
Sign up here for our daily Thrillist email, and get your fix of the best in food/drink/fun.