1. Myth: Skinny women have faster metabolisms.
Truth: The smaller your body mass, the fewer calories you burn.
Your metabolism is based on a ton of factors—including your height and weight. So the shorter, slimmer, and lighter you are, the fewer calories you probably need every day to maintain your weight, explains dietitian Tori Holthaus, RDN, LD, founder of YES! Nutrition. After all, it takes less fuel to run a Vespa than it does an SUV.
2. Myth: As you lose weight, your metabolism speeds up.
Truth: As you lose weight, your calorie needs typically decrease.
Remember how we said that smaller women actually need fewer calories to maintain their weight compared to larger women? Yeah, so unfortunately, for every pound of weight you lose, your calorie needs drop—and you have to continue cutting calories in order to keep losing weight, explains Jeff Johnsrud, MD, a weight-loss expert with St. Joseph Hospital in Orange County, California. Most women don't realize that, which is why weight-loss plateaus are so common, he says. Luckily, there is one caveat: If you gain lean muscle mass as you burn fat, your metabolism could end up staying the same—or even increasing. After all, every day, a pound of muscle burns about five to seven more calories than a pound of fat—and while taking up less space, says Wayne Andersen, MD, co-founder and medical director of Take Shape For Life online health community.
3. Myth: You can totally make over your metabolism by eating chili peppers and drinking green tea.
Truth: They'll give your metabolism a bump, but don't expect a miracle.
While these diet tricks can aid in weight loss, you'd have to spend all day chasing chili peppers with green tea to give your metabolism any noticeable boost, says Pamela Bede, a registered dietitian and board-certified specialist in sports dietetics with Abbott's EAS Sports Nutrition. For instance, you'd have to drink about two to four cups every day to burn an extra 50 calories a day. And one study published in The American Journal of Clinical Nutrition found that people who consumed chili peppers compounds every day for 12 weeks did lose some belly fat, but their resting metabolic rate didn't increase.
4. Myth: Your metabolism is destined to decline as you age.
Truth: You can keep your metabolism from taking a nosedive.
Can't "get away" with eating like you did back in high school? While women's metabolisms do tend to drop throughout the years, most of the decline is due to declines in activity (thanks, desk job) and muscle, Bede says. That's why, according to research from the Harvard School of Public Health, people who strength train put on less belly fat as they age compared to cardio bunnies. Plus, 2015 research in Endocrinology and Metabolism shows that increasing your protein intake can help you build more calorie-torching muscle as you age.
5. Myth: Your metabolism largely determines your weight.
Truth: Your metabolism is just one small factor in your weight-loss success.
"When people gain weight or have trouble losing weight, they tend to place too much blame on 'slow' metabolisms," Johnsrud says. But there's not that much difference between 'fast' and 'slow' ones, according to research from the University of Vermont. So, if by eating healthily and exercising, you burn more calories than you take in, you're going to lose weight—period.