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 we eat.
“Metabolism is the process by which our bodies convert what we eat and drink into energy,” says Melissa Perry, a registered dietitian with Orlando Health in Florida. “Our bodies use that energy converted from food and drink to power everything from breathing to moving and thinking.” This process runs continually inside the body to keep your organs functioning properly for survival and everything else you do every day.
“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.
“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.
How Many Calories Do You Really Need?
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 metabolism.
- 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′ 4″ tall and weighs 175 pounds only needs about 1,400 calories per day to keep the body going. By contrast, a 55-year-old male who’s 6′ tall and weighs 200 pounds needs nearly 1,800 calories a day to service 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 with a dietitian 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.
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 of us 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 it might just be mostly a fantasy.
“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.
How to Support a Healthy Metabolism
That said, you do 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.
1. Take Control
“There’s no strong evidence to show a magic food or supplement can boost your metabolism,” Perry says, “but 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 get a sense of how many calories your body needs and burns each day.
2. Eat Enough
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.
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 – remember that lean mass such as 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.
3. Boost Protein Intake
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.
5. Limit Sweets and Processed Foods
To support a healthy metabolism, adopt a “healthy diet filled with nutrient-rich foods,” Perry says. Look to consume mostly:
- Whole grains.
- Lean protein.
Perry says you should 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.”
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.
Taking in enough water is also part of the equation. Drinking water can actually support weight loss by raising metabolic rate slightly. Plus, drinking water helps the body flush out toxins and move waste products through the digestive tact, which can also support overall health and well-being and support the metabolism in its daily work.
7. Increase or Maintain Muscle Mass
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.
Muscle is 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.”
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.
8. Get Enough Rest
It’s not entirely clear what the relationship between sleep and weight control is, but it’s 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.
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.
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.