The answer lies with your metabolism, which is influenced by a variety of factors—some that you can control, and others you can’t. Before learning how (if at all) you can speed up metabolism, here’s what it is and how it works.
What Is Metabolism?
In very basic terms, metabolism is the way your body breaks down food for energy, says Audra Wilson, M.S., R.D., L.D., C.S.C.S., a bariatric dietitian at the Northwestern Medicine Metabolic Health and Surgical Weight Loss Center at Delnor Hospital in Geneva, Illinois.
Your body digests different macronutrients at different rates. For example, carbohydrates start to break down in your mouth while you’re chewing, thanks to salivary enzymes, says Wilson, but the bulk of absorption happens in the small intestine. Each macronutrient must be broken down to its most basic component—carbs into glucose, fats into triglycerides, and protein into amino acids—before it can be absorbed and used by your body for different processes, she adds.
In order to understand how this impacts your metabolism, first, you need to know your total daily energy expenditure or TDEE. Essentially, this is the total amount of calories you burn in a day portioned into two categories: Thirty to forty percent of these calories are based on your activity level (a long-distance runner is going to need more energy/calories than an office worker), and 60-70 of those calories are just the basic necessity to keep your body alive and functioning properly. Both vary from person to person.
The latter is something called your resting metabolic rate, or RMR. Basically, a higher RMR (or required calories to remain in homeostasis at rest) means you burn more calories at rest (i.e., you can eat more without gaining weight), whereas a lower RMR means your body burns fewer calories at rest (i.e., you have a “slow” metabolism, which can lead to weight gain if you’re eating more calories than you’re burning). Knowing your TDEE is important because it helps you determine how many calories you should be eating to meet your goal (whether that’s to lose, gain, or maintain your weight).
Many different factors go into your individual RMR: Your age, weight, gender, lean body mass (muscle), calorie intake, and activity levels. Hormones can have an impact, too, says Wilson. For example, if you have a hypoactive (underactive) thyroid, your RMR will be lower, but a hyperactive (overactive) thyroid can increase your RMR.
There’s no doubt about it: Metabolism is necessary for life. You just don’t have control over many of the factors that influence it.
Metabolism Factors You Can’t Control
Genetics: Like it or not, your metabolism is predominantly determined by genetics. “Your metabolism is probably very similar to that of your parents,” says Wilson. Some people are simply born with more lean body mass, and therefore have a higher RMR (and therefore, need more calories to maintain their body weight). (Related: 5 “Shape” Editors Took 23andMe DNA Tests and This Is What They Learned)
Environment: Even beyond blood, your philosophy around exercising and nutrition can be largely shaped by your relatives, as well. “The way you grew up, how much physical activity you did as a family, your diet habits—you get that from your family, too, and that can be transferred to your life as an adult,” says Wilson. (Related: 10 Ways Your Parents Can Screw Up Your Healthy Living Goals)
Age: Then there’s another pesky factor that affects metabolism: age. “Your basal metabolic rate [which is often used interchangeably with RMR] decreases every year after age 25,” says Alexandra Sowa McPartland, M.D., who’s dual board-certified in internal medicine and obesity medicine and owns SoWell Health, a weight-loss and metabolic wellness practice in New York.
Gender: Women also have a genetic disadvantage to men when it comes to metabolism. Even at their fittest, women have a lower percentage of muscle mass, says Dr. McPartland, so that will inherently create a lower RMR.
Metabolism Factors You Can Control
Before you go thinking the odds are stacked against you if you want to speed up metabolism, it’s not all bad. You do have some control over certain factors that can increase your RMR.
Muscle mass: The most important thing: Pick up the weights. “Muscle is more metabolically active than fat, so if you can increase your muscle mass, you’ll be able to raise your RMR,” says Dr. McPartland. (It’s worth noting that women especially take a big hit in muscle mass once they reach menopause, so building up and maintaining your strength in the first half of your life is key.)
Some studies also show that building muscle mass can help you maintain your RMR even through weight loss (more on that later)—another reason to focus on strength training. (Get started: Common Weight Lifting Questions for Beginners Who Are Ready to Train Heavy)
Nutrition and hydration: While you might have heard that there are certain foods that can speed up your metabolism, “that simply doesn’t happen,” says Wilson. You can, however, make a small impact by getting adequate protein, which has the greatest thermal effect. This means that “your body will burn a little more energy breaking down protein than carbohydrates and fat,” explains Wilson. In addition, protein helps you feel fuller longer, so you’re less likely to end up mindlessly munching.
And sorry, but drinking more water can’t speed up your metabolism, says Dr. McPartland. (Check out the other biggest myths about metabolism.) There’s no strong science to prove this happens, she says—although staying hydrated is, of course, a healthy thing to do overall.
Sleep: Clocking a solid 7-8 hours of sleep a night may also help you speed up your metabolism. If you’re not getting enough shut-eye, “it will throw off the balance of hormones that help your body burn fuel efficiently,” says Dr. McPartland. The same goes for stress. “If you’re incredibly stressed or not sleeping well, you’ll raise cortisol levels, which can cause your body to hold onto excess calories,” she adds.
Diet: Additionally, at least one study shows that intermittent fasting may have metabolism-boosting benefits. If you’re following a restricted-calorie diet, you tend to lose both muscle and fat; but with intermittent fasting, you’re able to maintain muscle mass at a greater rate, says Dr. McPartland. The research is still preliminary, “but this is one tool that might prove effective,” she notes.
How Metabolism Impacts Weight Loss
Here’s the weird thing: When you gain weight, you actually increase your RMR, because you have a higher body mass. Your body recognizes it has a larger mass to fuel, and whether that’s due to more fat or more muscle, it doesn’t matter here.
A higher RMR might sound good in theory, but it’s a problem if you decide to make a change and lose weight. When you drop pounds, your RMR will go back down, because it has less body to fuel, says Dr. McPartland.
And the reason for that it’s pretty instinctive. Your body thinks it needs to protect you from starvation (a process called thermogenesis), so your RMR drops more slowly to conserve energy, says Dr. McPartland.
This is where something dubbed “The Biggest Loser” effect comes in. When someone drops a large amount of weight, their RMR also drops dramatically. That makes maintaining that weight loss extremely difficult because, at that point, the body needs very few calories to match their low RMR, says Dr. McPartland. One study examining 14 former competitors found that six years after the show, metabolic adaptation contributed to each of them regaining much, if not all, of the weight they’d lost.
The lesson from this finding: It’s better to stay at a healthy weight than to fall into a pattern of yo-yo dieting, where you gain and lose the same pounds over and over again. (Related: How You’ll Know When You’ve Reached Your Goal Weight)
“The best way to do fight against natural decreases [in RMR] is to keep a metabolically healthy body from the beginning—focusing on staying healthy and preventing excess fat mass,” says Dr. McPartland.
The Bottom Line On Speeding Up Metabolism
Metabolism is a necessary function, and we have less control over it than we’d like—”so you shouldn’t use it as an excuse or blame it for weight gain,” says Dr. McPartland. You may find it’s easier for you to gain weight than a friend who follows the same exercise and nutrition program as you do, but that’s because you each have a different set of genes—not to mention, so many other lifestyle factors come into play.
“Comparison is the thief of joy when it comes to maintaining your health,” says Dr. McPartland. “If you focus on eating a healthful diet, exercising and doing strength training, sleeping well and decreasing stress, you can’t go wrong.”
Rather than constantly trying to speed up your metabolism, try shifting your perspective to view the process as a functional component of your health. At the end of the day, metabolism isn’t only associated with your weight. It’s what allows you to enjoy food and reap its energy benefits, and in turn, to be active and do all the things you love to do—and that’s something to celebrate, not lament.