It's an adage that gets repeated again and again: you can speed up your metabolism and lose weight by eating certain foods or taking supplements.
There's just one fairly large problem with that statement. Namely, that it's not true at all.
No matter what the claims on that bottle of raspberry ketone supplements say, nothing you eat can speed up your metabolism to the point of slimming down. What's more, obese people don't necessarily have slower metabolic rates than thin people. And science can prove it.
Metabolism boosters don't work for weight loss
First, let's explain what metabolism means: it's the biochemical processes by which your body turns what you eat (calories) into energy to keep you alive. Your 'resting' or 'basal' metabolic rate measures how many calories you burn while you're doing nothing: lying down in the morning before you eat and get out of bed. "It's the least amount of calories you're burning throughout the day, on average about a calorie per minute," said the Mayo Clinic's Dr. Michael Jensen, an endocrine specialist who has extensively researched metabolism.
While there are certain foods — caffeine, chili spices — that will speed that rate up just a little, the change is so negligible, it would never have an impact on your waistline.
"These ‘metabolism boosters' might raise your metabolic rate to 1.05 calories burned per minute for a very short period of time," he said. "To put that in context, if you walk really slowly you can generally burn three calories per minute."
Still, celebrity doctors like Dr. Mehmet Oz, have made this tiny change sound like the holy grail of weight loss and regularly encourage people to invest their money in so-called "metabolism boosters." Dr. Oz has endorsed everything from chili to chocolate and a rainbow of supplements as potential "belly blasters" and "mega metabolism boosters."
"Ninety percent of the stuff that (Dr. Oz) is claiming will boost your metabolism has zero scientific evidence behind it," said Dr. Jensen. "The 10 percent that does, the increase in metabolism you would get from it is so small that in a million years you're not going to have an effect on weight."
So "metabolism boosters" may not burn your fat but they will burn your money.
Everything you know about your metabolism is wrong
Besides the fact that metabolism boosting supplements may not work, there's also a surprising science behind that association between your metabolic rate and your weight.
"We've measured the resting metabolism in lots of skinny people and in lots of people with serious weight problems, and everything in between," said Dr. Jensen. "Whether you're above or below average, skinny or obese, as a rule you cannot say obese people have lower metabolism rates than lean people. That's just not true."
Research has shown that we do vary in how many calories we burn at rest — again, the basal or resting metabolic rate — but even big variations in that number aren't necessarily associated with being skinny or fat. In fact, bigger people often have higher metabolic rates than smaller people because their bodies need to do more work to sustain them.
For this reason, Dr. Jensen says you can't blame a slow metabolism for being overweight. That number on the scale is more probably related to things like appetite control, activity level, and calorie intake than anything else.
"We do know obese people tend to be up and about about two to two-and-a-half hours a day less than lean people," Dr. Jensen said. "My take is the amount of physical activity we do and the amount of calories we take in is far more important than what we do at rest."
So even though you can't control the speed of your metabolism, you can control how many calories you eat and what you burn through physical activity. When people ask Dr. Jensen how to boost their metabolisms, he tells them "go for a walk." That's something raspberry ketones just won't do. And it's free.