What does it take to keep the lights on in the human body? How does the body power everything from blinking and cell repair to washing dishes and running a marathon? In the simplest terms, all of these activities are powered by calories, which come from the food you eat. Generating that energy from calories happens via a process called metabolism.
“In short, metabolism is a term for all the chemical processes in our body that control our balance of
energy,” says Dr. Brian Quebbemann, a bariatric surgery specialist based in Newport Beach, California, and author of “World’s Greatest Weight Loss: The Truth That Diet Gurus Don’t Want You to Know.” When you eat food, your digestive system breaks it down into various components, and those get converted to energy by the body’s metabolic process.
This process runs continuously inside the body to keep your organs functioning properly for survival, and to power just about everything else you do in a day. “Your metabolism controls your body’s ability to generate energy,” which is used for literally everything from fighting infection, moving, staying warm and thinking. “When we have an unhealthy metabolism, all of these critical processes begin to fail.”
“However, when most people hear the word ‘metabolism,’ they usually think about weight and calories,” says Kacie Vavrek, a sports dietitian at the Ohio State University Wexner Medical Center in Columbus.
But as New York City-based registered dietitian Jamie Feit of Jamie Feit Nutrition LLC, notes, “metabolism is so much more than weight on the scale and calories consumed.” It powers all bodily functions.
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How Many Calories Do You Really Need?
Every body needs a certain number of calories each day to maintain cellular function. “Your resting metabolic rate is the rate at which your body burns energy when it’s at complete rest. Even at rest, you’re burning a lot of calories for bodily functions like breathing, digesting, adjusting hormone levels and growing and repairing cells.”
These maintenance functions in the body are actually what burns the vast majority of the calories you ingest, not that walk you took after lunch. As such, “when someone talks about their metabolism, they’re often referring to their resting calorie burn,” Vavrek adds.
Your resting metabolic rate is largely determined by three factors:
- Body size and composition. People who are larger and have more muscle mass tend to have a higher metabolic rate.
- Sex. Males tend to have less body fat and more muscle mass, leading to a higher metabolism.
- Age. As you age, you lose muscle mass and your metabolism slows.
For example, a sedentary 55-year-old woman who’s 5 feet, 4 inches tall and weighs 175 pounds only needs about 1,400 calories per day to keep her body going. By contrast, a 55-year-old male who’s 6 inches-‘ tall and weighs 200 pounds needs nearly 1,800 calories a day to meet the basic needs of maintaining the body at rest. When you add in exercise or physical activity, those needs increase no matter who you are.
You can calculate your basal metabolic rate – meaning the number of calories required to keep your body functioning at rest – with an online calculator that will give you a rough estimate of the number of calories you need each day to fuel basic bodily functions.
You can also visit a dietitian or nutritionist for a more tailored and accurate test that will assess your individual body composition and physical activity levels, rather than just calculate a number using a set formula that considers height, weight, sex and age. This might be useful for those who are very active or if you’re trying to lose weight.
Metabolic rate figures are highly individual and they change over time. “How much you burn each day is a function of age, your weight and activity level,” says Dan Daly, a coach, trainer and co-creator of the Equinox Group Swim Program EQXH2O based in New York City. “Metabolism declines about 10% a decade. So, if you’re following a 2,000-calorie per day diet, that’s about one to two apples less per day,” each decade.
However, despite this natural slow down, Daly notes that weight gain isn’t always the fault of age. “Metabolism doesn’t slow down as much as it’s blamed for. Weight goals are more likely a product of a calorie surplus from eating and a decline in activity as we get older.”
Can I Change My Metabolism?
Many people have been seduced by the idea of revving up or increasing the metabolism as a means of getting control over that aging process and trimming the waistline. But this might just be a fantasy, for the most part.
“Metabolism is determined by our genes, and there’s not a lot that we can do to significantly change our metabolism,” Vavrek says. “We might see small or temporary changes in metabolism by diet or muscle mass changes, but usually you won’t see significant changes in metabolism.”
Vavrek notes that while many people blame a “slow metabolism” for weight problems, “the truth is that a ‘slow metabolism’ is rarely the cause of weight gain. It would be more beneficial to focus on calorie intake and regular exercise than on ways to boost metabolism.” That’s because it’s unlikely that you’ll be able to “boost metabolism” enough for significant, long-term weight loss.
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How to Support a Healthy Metabolism
Feit, who also serves as nutritional expert with Testing.com, a health information web resource, agrees that metabolism is “mostly genetic,” but notes “there are changes that can be made in the diet as well as exercise,” that can alter metabolic rate to some degree.
After all, you have control over what and how much you eat and how much you move. “The more active we are, the more calories we burn,” Vavrek says.
To support a healthy metabolism, consider making the following eight dietary and activity changes:
- Take control.
- Eat enough.
- Boost protein intake.
- Eat breakfast.
- Limit sweets and processed foods.
- Stay hydrated.
- Increase or maintain muscle mass.
- Get enough rest.
“There’s no strong evidence to show a magic food or supplement can boost your metabolism,” says Melissa Perry, a registered dietitian with Orlando Health in Florida. However, “you can control what you’re eating and your physical activity.”
Make a plan and keep track of how much you’re eating, how much you’re moving and use an online calculator and a fitness tracker to get a sense of how many calories your body needs and burns each day. Feit notes that engaging in “daily activity, especially weight-bearing exercise can help you see small changes.”
Starvation diets cause the body to slow the rate at which it uses energy by shutting down nonessential processes. This slows the body’s overall metabolic rate, which in turn makes it more difficult to lose weight. It’s a cruel irony that many yo-yo dieters know all too well.
What’s more, “regularly skipping meals and cutting calories too low can lead to muscle loss, which can negatively impact metabolism,” Vavrek says.
But, “you can support metabolic function by eating,” Daly says. “The thermic effect of food, (or the energy it takes to digest and convert food into energy) is responsible for 10% of total caloric expenditure daily.”
In other words, that means that for a person consuming 2,000 calories per day, just consuming and digesting that food will burn about 200 calories, leaving 1,800 left to be gobbled up by the brain, heart and other internal organs as well as any physical activity you engage in.
All that said, intermittent fasting appears not to have a negative impact on metabolism like starvation diets do. Some studies have suggested, in fact, that intermittent fasting can help rev up the metabolism. This is believed to be connected to how intermittent fasting can preserve lean body mass (aka muscles and bone) – remember that muscles burn more calories than fat. The fact that fast periods are interspersed with times when you take in more calories, rather than chronically limiting calories, means that intermittent fasting seems to help dieters retain more muscle mass than when following a starvation diet.
Not all food takes the same energy to convert, Daly notes. “Protein is the most metabolically costly to digest, and some fibrous fruits and vegetables cost more calories to digest than they actually contain.” These so-called negative calorie foods include high-water-content vegetables such as cucumbers, celery and lettuce.
Increasing the amount of protein in the diet doesn’t cause a significant increase in metabolism and it’s a temporary alteration, but Vavrek notes that “consuming adequate protein in your diet will help to maintain muscle mass.”
You don’t have to go overboard with protein intake, but making sure you’re getting enough – 0.8 grams of protein per kilogram of body weight per day is typically recommended for the average adult – can help support the body’s need to repair itself. To convert that into pounds, a 165-pound person would need about 60 grams of protein per day.
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Many dietitians recommend starting the day with a healthy breakfast that contains protein, fiber and some fat to help you feel fuller longer and to ramp up that thermic effect. Get your body fueled up for the day ahead.
Feit also warns that “eating too little can slow the metabolism and put the body into ‘starvation mode’ where the body will slow the metabolism. The body uses calories to digest food, so it’s important to make sure to eat enough.” Starting off on the right foot each morning with a healthy breakfast can help.
“Supporting your metabolism mainly requires eating foods that provide healthy energy,” Quebbemann says. This means steering clear of highly processed foods that contain “artificial chemicals that damage the body.”
He explains that “processed food has been changed chemically to make it easier to store, make it taste sweeter, make it easier to eat and make it more profitable to sell. The more a food is processed, the more likely it is to contain chemicals that damage our body without providing energy. The more processed a food or snack is, the more damage it causes when we eat it.”
What’s more, ultra-processed foods are typically very easily broken down by the body into sugar, which means your body doesn’t use as many calories to process these items as it does when digesting unprocessed, whole foods.
Perry recommends adopting a “healthy diet filled with nutrient-rich foods,” including:
- Whole grains.
- Lean protein.
Fill your plate with these nutrient-rich foods instead of high-calorie and low-nutrient foods “by limiting your intake of highly processed foods, such as sweet baked goods, processed meats and sugar-sweetened beverages.”
For Quebbemann, the formula is simple: “If it doesn’t live on the earth, swim in the ocean, or grow naturally from the earth, avoid it. How many times have you seen a field of Twinkies or Doritos? Right, never. These foods are highly processed and, if you eat a significant amount of them, your metabolism will get sick.”
Taking in enough water is also part of the equation, Feit says, noting that staying well hydrated can also keep your metabolism humming and “is good for weight loss.”
That’s because drinking water actually raises the metabolic rate slightly. Plus, drinking water helps the body flush out toxins and move waste products through the digestive tract, which can also support overall health and well-being and the metabolism in its daily work.
To support the changes you’re making in the kitchen, you should also seek to increase “lean muscle mass through exercise,” Perry says. Strength training or weight lifting can help build muscle that can burn more calories.
“Almost all exercise can boost your metabolism, at least temporarily,” Quebbemann says. “When you exercise, you burn more calories, but just as importantly, after you’re done, your body will require more calories to recover from the exercise.” Higher intensity activities can further speed up this process.
Muscle is also more metabolically active than fat, meaning that lean muscle mass burns more calories at rest than fat does. Vavrek notes that the biggest increase in calories burned occurs during exercise when the person has more muscle mass. It might not be a huge figure, but it does “highlight the importance of regular exercise for weight control.”
“All exercise boosts metabolism, but strength training and high intensity interval training may be more disruptive to (and thus increase) metabolism,” Daly says. This is because the body will have to work harder to repair tissues after a strength training session, and your oxygen consumption is typically higher after high-intensity cardiovascular training, which can also increase your metabolic rate temporarily.
“Eating regular, balanced meals can help you to maintain muscle mass as well,” Vavrek adds.
And Quebbemann notes that it’s important to remember that exercise can only boost metabolism as an ongoing endeavor. “All that exercise you did on the football team in high school doesn’t do much to help your metabolism when you’re 40.”
It’s not entirely clear what the relationship between sleep and weight control is, but “the body repairs itself at night so it’s super important to make sleep a priority for all metabolic processes to work,” Feit says.
While you sleep, your body is busy repairing tissue and removing waste products. You need those processes to function optimally to support overall health, wellness and your metabolism.
It’s also been noted that people who sleep poorly or have disrupted sleep patterns tend to weigh more than those who get enough rest. They’re also at higher risk of a variety of chronic diseases including diabetes and cancer.
A Race Against Time
Moving more and eating well become more important with each passing day. “Muscle mass can decrease with age, which can slow your metabolic rate. But exercise can help boost it,” Perry says.
Still, Vavrek warns to be wary of any outsized claims for diets or products that purport to boost metabolism. “There’s no magic supplement that will boost metabolism. This is a common marketing strategy among supplement companies. Products marketed to speed up metabolism are usually a scam.” If it sounds too good to be true, it probably is.
Daly sums up the advice on supporting a healthy metabolism by saying: “Move more, eat often, hydrate and sleep. From an evolutionary standpoint, we were once hunters and gatherers, spending large amounts of time moving to find scarce food and taking time to prepare it. Modern work and convenience have left us largely sedentary, which is compounded by the abundance of calorically dense prepared food. This has left us in a caloric surplus, overfed and under active,” all of which can add up to excess weight.
Bottom line, Quebbemann says, is to think of your body like it’s a car. “If you put bad gas and dirty oil into your car and you don’t take it into the shop for routine maintenance, it’s going to break down more often. If you don’t do much to maintain your body, don’t be surprised when it breaks down.”