We’ve all heard the adage that gaining weight in the middle-age years and beyond is inevitable, particularly for women enduring the hormonal shifts, sweat-soaked sheets, insomnia, wicked moodiness, and pregnancy-level fatigue of menopause. We’re told to expect and accept that we can’t boost metabolism after 40—that biology happens.
Until the publication of a 2021 review in Science, whose data busted the myth that your resting metabolism starts to slow at age 40.
The paper reviewed data from 6,500 participants, from 8 to 95, and determined that resting metabolic rate remains stable in adults ages 20 to 601 before declining less than 1% per year after age 60.
This turns what we think we know about aging and metabolism upside down. That’s not a bad thing. It levels the playing field and can stop you from leaning on your “age” as a reason why those extra pounds can creep up (unless you’re over 60).
There are things you can do to elevate your metabolic rate to burn more energy at rest. Those strategies follow the quick need-to-know basics section about metabolism.
We expend energy in three ways:
Dietary-induced thermogenesis refers to the energy you expend breaking down food.
Before you get too happy about the fact that we burn calories digesting food, the amount of calories is pretty small. One scientific paper suggests a mixed diet at energy balance burns 5–15% of total calories on digestion2. If you ate about 1,800 calories, that would amount to 90–270 calories, which is less than the calories in your venti vanilla latte3.
This eat-food-and-burn-calories idea has legs, though. If you’re into it, focus on protein. High-protein meals are the most thermogenic4 (compared to high carb or high fat) and promote the highest sensation of fullness.
Just keep in mind that your body can only use a certain amount of protein in one sitting—about 20–30 grams of protein in one hour, depending on your daily needs (based on activity level, gender, muscle mass, etc.).
You also burn calories while at rest; called resting metabolic rate, your body uses energy to think, build new cells, stay warm… basically all of the functions to keep you alive.
Your resting metabolic rate (aka resting energy expenditure) usually accounts for the largest portion of your total daily energy needs. As the name implies, it’s the amount of energy required for functioning at rest.
Resting and basal metabolic rates (BMR) are similar, but BMR calculates the number of calories your body burns reclining at complete rest.
Resting metabolic rate may be a better indicator of your daily energy needs. A high RMR means your body requires more calories for basic functions—it also means your metabolism operates efficiently.
How do you calculate your resting metabolic rate? The method to get the most accurate results involves calorimetry, a test that measures the amount of heat you produce when enclosed in a small chamber to calculate your energy expenditure.
So… a pricey and impractical calorimetry test probably isn’t happening anytime soon for you. Mathematical equations5 exist that factor your gender, height, weight, and age to guesstimate your RMR. Online calculators6 can provide a guide as well.
These tools can provide a flawed estimate of how many calories you burn at rest because they don’t include your lean body mass. They also don’t consider your ethnicity or epigenetics, which could modify metabolic pathways on a cellular level7. (To be fair, it’s not entirely realistic to expect a static mathematical equation or general online calculator to spit out accurate RMR numbers.)
More to the point, even if you don’t know your exact RMR, you can find a guesstimate. The main takeaway about RMR: It’s the part of your metabolism that can burn the most energy. Increase your resting metabolic rate, and you’ll likely burn more calories every day just chillaxin’.
The previously mentioned data review published in Science reported that total daily energy expenditure—how much energy your body needs to fuel activity, stay alive, and operate—increased with more fat-free mass8 (aka lean body mass).
A small study on young adults found that lean body mass had the strongest correlation to participants’ resting metabolic rate9, as did gender. Researchers posited that while men generally have a higher RMR, their data suggested it was because men tended to have more lean muscle mass than women.
Fat-free mass includes your muscles, organs, bones, skin, connective tissue, and water—essentially, all of the things that make up your weight minus your body fat.
So, how do you get more fat-free mass? While you can’t grow more bones or organs, you can build muscle. You can do this in a variety of ways, all of which can be combined to provide a well-rounded strength training program.
Ways to build muscle:
Several strength-building techniques can be combined with the methods outlined above, such as progressive overload, focus on the eccentric phase of an exercise, integrate drop sets, vary the duration of your work and rest times… the list goes on.
These principles can be used to optimize an existing strength training program; if you’re a beginner, stick to the basics and concentrate on completing exercises with proper form. Prioritize safety and the health of your joints rather than straining to lift more weight. As you get stronger, the effort required to execute the exercises will get easier—that’s your cue to add weight or more reps.
Good news: strength training may boost your VO2 max11, so if you’re already doing that, keep it up.
VO2 max means the volume of oxygen your body uses while exerting maximum effort (v = volume, O2 = oxygen, max = holy-smokes-that-was-hard effort). This measurement indicates cardiovascular fitness and aerobic endurance.
What type of exercise boosts VO2 max? High-intensity interval training12 (HIIT), endurance training, and possibly resistance training (depending on the intensity).
A form of interval training, HIIT workouts alternate relatively short bursts of anaerobic exercise (close to max effort) with recovery periods. Endurance training engages the aerobic system to increase endurance, meaning a more steady-state, moderate-intensity with a longer-than-HIIT duration to build stamina.
As one study of 271 participants showed, those with higher resting metabolic rates also had significantly higher VO2 maxes13 and lean body mass. People with lower resting metabolic rates also had higher body fat mass and belly fat.
An exercise routine of 20–45 minutes performed at 60–75% of max heart rate followed three to five times a week increased RMR and VO2 max14 in men and women who were sedentary and overweight before the study. Similar findings were reported in a smaller study on moderately obese women who showed a significant rise in RMR15 after 11 weeks of five hours per week of aerobic exercise at about 50% VO2 max.
Ways to build VO2 max:
Building VO2 max is challenging so if you’re a beginner, ease into it. Start with moderate-intensity endurance training a few times a week; build your stamina over time by adding a little bit of extra time or distance to your sessions. Get a solid foundation of endurance work for a few months before adding HIIT-style intervals.
You’ve heard that moving your body burns calories; that’s not surprising. What may be, though, is the kick-in-the-pants reality that you don’t necessarily burn more calories the more or longer you work out.
A study of 332 adults living in five populations showed that total energy expenditure, or calories burned, plateaued above moderate activity levels17. Human and animal studies show that energy allocation for functions performed at rest may be reduced when physical activity increases. This adaptive measure results in decreased activity energy expenditure18.
Unless you are training for an endurance event, CrossFit competition, or another performance-oriented feat, you’d be better off sticking to moderate amounts of activity.
For good health, the World Health Organization19 recommends that adults ages 18–64 should:
Non-exercise activity thermogenesis (NEAT) entails the calories you burn while not exercising, eating, or sleeping. It’s the movement between your workouts that can add up to more energy burned all day long.
Have you ever wondered how a lithe mom in leggings and a tank top can stay trim while cradling a toddler on her hip seemingly at all times? She’s chasing the kids, pushing the baby in a stroller while walking the dog, cleaning up constant messes, lifting heavy grocery bags, carrying loads of laundry up and down the stairs, and longing for a few minutes to sit on the couch undisturbed each day. In short, her day is packed with NEAT.
One small study showed that NEAT increased fat oxidation20 the day following a high-fat meal. The Mayo Clinic estimated that NEAT movements could result in a max of 2,000 calories burned per day21 beyond the basal metabolic rate.
Keep in mind that NEAT is one component of energy expenditure, but not a guarantee that you’ll burn more calories every day if you move more.
Research shows that a long-term increase in activity doesn’t necessarily translate into a boost in total energy expenditure because other components of TEE may decrease in response. One study of 1,754 people living “normal lives” suggested that only 72% of the extra calories we burn from increased movement22 translates into more total calories burned.
This isn’t meant to dissuade you from moving around more, but rather to use this knowledge to build a movement plan that works for you. Don’t have time for a 30-minute run today? Try to do three 10-minute brisk walks between meetings and other obligations. When you stop at the store on the way home, park farther away from the store entrance, leave the shopping cart outside the store, and carry your bags to the car.
As with many things in life, more isn’t always better. It’s just more. When it comes to matters of metabolism, focus more on: