Everything you need to know about your metabolism, according to a dietitian

Your burning questions about metabolism and weight loss — answered.
bowls of yogurt
Eating foods high in protein, like Greek yogurt, can slightly boost the thermic effect of food — the calories you burn from digestion.Michelle Arnold / EyeEm / Getty Images
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By Samantha Cassetty, RD

If you’ve ever been grabbed by headlines that claim to help you boost your metabolism, burn fat faster, or torch calories by taking a pill or eating some miracle food, I’ve got a spoiler alert: Your metabolism is pretty tightly regulated and there’s little you can do to speed things up.

This may come as a big surprise (and a big buzz kill!) but it doesn’t mean that you can’t lose weight, which is why most people are concerned with their metabolism in the first place. Here are some answers to your burning questions about metabolism.

What is your metabolism?

Your metabolism is made up of a few components:

  • Your basal metabolic rate, or BMR, basically refers to the calories you burn just to stay alive. Your body is really cool and does some pretty amazing things to keep you alive and functioning! It’s always hard at work — say, enabling you to breathe, pumping blood to your heart, and so much more — so you’re always burning calories. Your BMR accounts for 70-80 percent of the calories you burn and it’s highly variable from person to person. Age, gender, genetics, hormones and muscle mass play a role in your BMR.
  • The thermic effect of food (TEF) is a complicated way of referring to the calories you burn digesting food. This process accounts for about 10 percent of the calories you burn.
  • Non-exercise activity thermogenesis — or NEAT — is how we refer to the calories we burn through non-sports activities. This could include cleaning your kitchen, trying on clothes at the mall, and even just fidgeting. What’s truly neat about this is that this type of activity accounts for 10-20 percent of the calories you burn, and studies suggest that you can burn around 800 extra calories per day moving around a bit more, for example by doing things like using a standing desk, taking the stairs instead of the elevator, and accumulating activity during routine chores, like grocery shopping and cleaning the kitchen.
  • Exercise activity thermogenesis is just a complicated way of saying physical activity, and it’s just what you’d expect — the calories you burn when you’re purposefully trying to break a sweat. Going for a power walk with a friend would count as physical activity but strolling around the grocery store — even while tracking and accumulating steps — would fall in the NEAT camp. If you’ve been keeping tabs on the math, you can see that physical activity can only account for about 5-10 percent of your metabolism, though taken together with NEAT, can add up to about 30 percent of your calorie burn.

Can I exercise more to boost my metabolism?

The short answer is not by much. What this means is that while the impact may not be dramatic, it’s a factor that’s well within your control. In addition to burning some calories, a big advantage of exercise is that it helps you increase your muscle mass. The more muscle you have, the higher your BMR will be, since muscle is a very active tissue that demands a lot from your body. Since men have more muscle mass than women, they also have higher metabolisms than women.

Exercise only accounts for a fraction of calories burned whereas eating accounts for all of the calories you consume.

However, unless you’re a power lifter (and let’s face it, most of us aren’t), this metabolic boost is pretty small. It’s not meaningless, but if all of your weight loss efforts are spent at the gym, you’re only putting in 5-10 percent of the work! Another way to put this: Exercise only accounts for a fraction of calories burned whereas eating accounts for all of the calories you consume. This (among other reasons) is why you should enjoy your movement experiences rather than torturing yourself in the name of burning calories.

Can eating small, frequent meals boost my metabolism?

You might expect it to, but more commonly, I’ve seen this lead to overeating, and therefore, weight gain. Remember that real life isn’t like lab life, and even a review of studies that examined the effect of grazing found that the majority of time, it doesn’t help.

What can I eat to speed a sluggish metabolism?

There are a few factors that can influence and optimize the TEF. You’ll get a slight boost if you’re eating sufficient protein (foods like chicken, tuna, eggs, chickpeas and Greek yogurt), and this macro has another advantage. It keeps you fuller, longer, so it helps manage hunger.

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Swapping processed and manufactured foods for whole ones is the other way to maximize the metabolic boost you get from eating. Think of it like this: Once food is processed, it’s much easier for your body to grab the energy (another way of saying ‘calories’) it needs. That means you’re not going to burn as many calories from eating processed foods as you are from eating foods in their whole form.

What about green tea, apple cider vinegar, and cayenne pepper?

Let’s get something clear: There are no shortcuts when it comes to losing weight. It’s true that studies show that green tea and cayenne pepper may help, but the studies are short term or take place in test tubes or rodents, and they tend to use these substances in supplement form (rather than the food form, which is how most people consume them). And most importantly, the help is minuscule. It likely wouldn’t translate to any meaningful, long-term benefit.

There’s also evidence that apple cider vinegar may help with weight loss, but there’s evidence it can cause tooth erosion or esophageal damage so it’s not a strategy I’d advise.

Finding a sustainable place on the scale isn’t a race to drop pounds, and we don’t really know the long-term safety of these short-cut solutions. Instead of spending your money on pills, enjoy these ingredients as part of a healthy eating pattern. Try a vinaigrette made with apple cider vinegar, or use it to dress a potato salad. In the latter example, it makes some of the starch indigestible, which then allows that undigested starch to become the perfect fuel for your gut bacteria.

Drink unsweetened green tea (hot or iced) instead of popping supplements, and if you like things spicy, by all means, add some cayenne pepper to your meals! But if you don’t care for spicy food, there are far better ways to lose weight than to spice your meals.

Does yo-yo dieting kill your metabolism?

It doesn’t appear that it kills your metabolism in the way that you’re thinking about it. Think of it like this: After gaining weight, your body feels at home at its new size. When you begin to lose weight, your body begins to make adaptations because it recognizes there are changes happening at home. These adaptations manifest as changes in the hormones that make you hungrier, and when you feel hungry, the typical response is to eat. This makes it hard (but not impossible) to keep the weight off.

The other irony is that as you lose weight, you actually need fewer calories to maintain your smaller frame. This is where metabolism comes into play. Since your body is smaller, your metabolism adjusts to your new size, so on top of being hungrier, you require less food. Also, if you aren’t eating carefully while trying to lose weight, you may lose some muscle, which will impact your metabolism.

There may be some exceptions, though. Some studies point to the fact that extreme dieting and weight loss — a la the "The Biggest Loser" contestants — might cause a dip in your metabolism below what would be suggested based on your new size.

One other thing to note here: While yo-yo dieting might not ruin your metabolism, it isn’t healthy. This habit is linked with an increased risk of heart disease.

Do thin people have faster metabolisms?

Again, not for the reasons you might think. Smaller people actually have slower metabolisms since your BMR is related to your size. Recall that when you lose weight, your BMR adapts to compensate for a smaller body. However, we all know people who can seemingly eat anything they want and not gain weight. (Yes, these people annoy me, too!) Though you might expect these people to have higher metabolisms, new research suggests that they may actually have genetic variations that are equivalent of hitting the metabolic lottery! Something is working in their favor, though we haven’t pinpointed exactly what that is yet.

One more thing on body size: it’s not an indicator of your health. If you’re looking at two houses, does a blue house say anything about the foundation when compared to a red house? It’s the same thing with bodies. Some healthy people have larger bodies and some healthy people have smaller bodies, and you can be naturally slim and have heart disease or diabetes, just as you can have a larger body and be healthy.

Is there anything else I can do to boost my metabolism?

We’re learning more and more about the roles of sleep and your microbiome on the metabolic pathways that influence your weight. For starters, guard your sleep! Aim for the recommended 7 to 9 hours of sleep each night. If you have trouble hitting sleep targets, you can try establishing some healthy sleep habits. A few to start with: Cut out caffeine after mid-day, create a relaxing bedtime ritual (reading and meditation are some ideas), and resist the urge to scroll through email or social media within an hour of bedtime. Also, be careful with booze, since going above the recommended caps (one drink a day for women, two for men), interferes with restorative sleep.

The advice to drastically limit sugary and processed foods and focus instead on food in its whole form is a great step towards keeping your microbiome healthy. Other things you can do: Embrace a variety of fiber-rich foods (think: veggies, fruits, beans, nuts, seeds and whole grains) since these foods get broken down into chow for the beneficial bacteria in your gut. Also, enjoy some naturally probiotic-rich foods, such as plain Greek yogurt or sauerkraut. These types of foods plant more beneficial bacteria in your gut. Your microbiome has a huge impact on your overall health so this is good, all-around advice, regardless of your metabolism.

WHAT A NUTRITIONIST WANTS YOU TO KNOW

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