People talk about their metabolism a lot. You'd think they actually understand it.

But often that's not the case. Here are four things you should know about the M-word:

Burning Truth No. 1: Skinny People Have Fast Metabolisms

VERDICT: Sometimes

"There are slim people with slightly low metabolisms who just don't eat very much," says Michael Jensen, M.D., an endocrinologist with the Mayo Clinic. "And there are heavy people with really high metabolisms who eat a huge amount." (Create your toughest workout with these 10-minute routines!)

Burning Truth No. 2: Lean Tissue Burns More Calories Than Fat Does Even While You're Asleep

VERDICT: True

"Your brain, heart, liver, and kidneys use a lot of energy, even when you're lying still," says Dr. Jensen. Muscle and the GI tract don't use much at rest; fat burns practically nothing. His estimate: You burn about a calorie per minute at rest. A quarter of that is torched by muscle, and 1/50th of it is burned by fat. (Is your workout burning flab -- or just burning up your time? Don't fall for these 5 Fat-Loss Myths.)


Burning Truth No. 3: Some Guys Can Only Slim Down By Slashing Calories

VERDICT: False

"In 30 years I've never seen anyone with a truly low metabolic rate," says Dr. Jensen. "People who think they need an 800-calorie diet often have resting metabolic rates of 1,500 calories."

So why can't they slim down? They're often eating many more calories than they realize. His fix: Accurately record everything you eat for two weeks. Unhealthy trends may emerge. (Are all calories created equal? Click here for The Truth About Calories.)

Burning Truth No. 4: Cutting 500 Calories A Day Means You'll Lose A Pound A Week

VERDICT: Not Quite

A pound of fat does equal 3,500 calories, and you may lose a pound the first week. "But when you eat less, you lose lean tissue, so your basal metabolic rate goes down," says Dr. Jensen.

Surprise: You may gain more than a pound after a 3,500-calorie pig-out, since calories stored as sugar cause you to retain water. (Eat 30 percent less with this easy research-proven trick: The Easiest Way to Shrink Your Gut.)

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