We all know someone who seems to be able to eat anything they want without gaining an ounce. On the flip side, we all know someone (or are someone) who feels like they can gain five pounds just by looking at a cheeseburger.
You’ve probably heard people in both camps talk about metabolic rate — those who don’t pack on pounds easily credit their fast metabolism, while those who have trouble losing weight blame a sluggish metabolism. But how much does metabolism really affect weight? And can we change our body’s metabolism? Here’s what you need to know.
What Is Metabolism?
Metabolism is a term that encompasses all of the chemical reactions that produce energy or utilize energy in the body — including converting calories from food into the fuel we need to survive.
Your body requires a bare-minimum number of calories to support its basic functions. “Even when you’re at rest, your body needs energy for all its behind-the-scenes functions, such as breathing, circulating blood, adjusting hormone levels, and growing and repairing cells,” says Maria Faires, RD, personal trainer, and advanced health and fitness specialist in Washington.
The rate at which you burn calories through basic functioning is known as your basal metabolic rate (BMR). Unless you enjoy complicated math problems, your best bet is to use an online calculator that calculates your BMR based on your height, weight, age, and sex. (Some online calculators will also factor in your daily activity level to determine how many calories you should consume each day to maintain your current weight.)
But Carrie Dennett, MPH, RDN, and nutrition expert based in Seattle, warns that metabolism is a highly individual process. “You are not an equation,” she said. “A set of numbers can’t know the sum of all the chemical changes going on in your cells.”
For the most accurate picture of your metabolism, consult your doctor for a BMR test. During this test, a special breathing mask monitors the amount of oxygen your body utilizes and how much carbon dioxide it produces, and an electrocardiogram measures your heart rate. Your doctor can then use the results as a baseline to determine how many calories you should consume each day, based on your activity level and your weight goals.
How to Boost Your Metabolism
There are a number of factors that can affect your metabolism, including age, genetics, eating habits, and underlying conditions such as thyroid issues.
But unless you have an underlying condition — or are taking a medication that causes weight gain — you typically have some control over your metabolism via diet and exercise. “It is [often] your caloric intake and the amount of physical activity you do that eventually determines how much you weigh,” Faires says.
How Diet Affects Metabolism
While research suggests that eating certain foods, like whole grains and protein, can temporarily increase your metabolic rate — a phenomenon referred to as the “thermic effect of food” — that doesn’t mean you can “supercharge” your metabolism and magically burn off extra calories just by loading up on these foods.
Still, eating a healthful, wholesome diet may benefit your metabolism. A diet based in vegetables, fruits, whole grains, and lean proteins “may give you a bit of a [temporary] metabolic boost compared to a diet full of refined grains and sugars,” Dennett says. One study found that postprandial energy expenditure — the calories burned after eating a meal — was 50 percent lower after eating processed foods than after eating whole foods.
It’s also important to make sure you’re getting enough calories. When you restrict calories too much, your body adapts as if it’s trying to survive a famine. Levels of leptin (the “fullness hormone”) decline, and your metabolism slows to conserve energy.
So instead of focusing on extreme calorie restriction, which can backfire, make sure you’re eating healthful foods — and enough of them.
How Exercise Affects Metabolism
You may have heard that “muscle burns more calories than fat” — but while this is technically true, the difference in BMR won’t be enough to produce any significant weight-loss results. In other words, building muscle won’t give you a lightning-fast metabolism.
But exercise can help enhance metabolism in other ways. Not only will you burn calories while exercising, Dennett says, but you’ll also burn more calories for up to 72 hours after you work out as your muscles repair themselves and grow. (HIIT workouts in particular have been found to increase metabolism post-workout.)
And don’t worry that exercise will make you hungrier — research actually shows that exercise doesn’t lead to overeating, and may even help regulate appetite.
Bottom line: Even if building muscle won’t turn you into a lean, mean calorie-burning machine, it’s still worth doing for all the other healthy benefits you get. “Exercising to develop greater strength and stamina — not just to maximize calorie burn — is key,” Dennett says.