Metabolism refers to the chemical processes inside the body that convert food into energy in order to keep you alive. Not only does the body require energy to be physically active but breathing, thinking, growing and digesting food also require energy. Another word for energy is calories, so you can think about metabolism as the number of calories your body needs to keep you alive and functioning.
Read More: What Exactly Is Metabolism—and Can You Change It?
How to Calculate Metabolism
Resting metabolic rate (RMR) measures how many calories your body burns at rest. Basal metabolic rate (BMR) measures how many calories your body needs to perform its most basic functions like breathing. Many experts use RMR and BMR interchangeably because they only have slight differences.
The most precise way to measure BMR and RMR is in a laboratory setting. To do so, you breathe into a mask called a calorimeter, which calculates your rate of breathing and uses it to measure how many calories you burn at rest. If measuring BMR, you may be required to fast beforehand and sleep at the lab, while you wouldn't necessarily have to do these things if measuring RMR. RMR is usually measured first thing in the morning.
While the calorimeter is the most precise way to calculate BMR and RMR, most people don't have access to get their metabolism measured in a lab. Thankfully, there are equations and online calculators that provide a pretty good estimate in just seconds.
The most widely accepted BMR equation is the Mifflin-St Jeor formula. In order to do the calculation, you'll need to know a few things first: your weight in kilograms and your height and both inches and centimeters.
1. To find your weight in kilograms, use this simple equation:
Kilograms = your weight in pounds ÷ 2.2
So, if you weigh 165 pounds, your weight in kilograms would be 75 kilograms.
2. To find your height in inches, use this simple equation:
Height in inches = (height in feet x 12) + remaining inches
So, if you are 5 feet 7 inches tall, your height in inches would be 67 inches.
3. Find your height in centimeters, using this simple equation:
Height in centimeters = height in inches x 2.54
So, for someone who is 5 feet 7 inches tall, their height in centimeters would be 170.2 centimeters.
Now, plug it all into the BMR equation:
For men:
BMR = (10 x weight in kilograms) + (6.25 x height in centimeters) – (5 x age in years) + 5
For a 35-year-old man, using the height and weight from above, the BMR would come out to be 1,644 calories.
For women:
BMR = (10 x weight in kilograms) + (6.25 x height in centimeters) – (5 x age in years) - 161
For a 35-year-old woman, using the height and weight from above, the BMR would come out to be 1,478 calories.
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Total Daily Energy Expenditure
After you know your BMR, you can use it to figure out how many calories to eat each day, whether your goal is to lose, gain or maintain your weight. While weight loss is not as simple as calories in and calories out, calories can be a starting point, especially if you've never paid attention to them before.
Once you know your BMR, there's a little more math to do. Remember, BMR is simply the calories your body needs to survive. Note: This is not the number of calories you should be eating each day. You need more calories, because BMR only makes up 60 to 70% of total daily energy expenditure (TDEE). Another 10% of the calories the body burns each day comes from the thermic effect of food (TEF), or how many calories your body burns digesting food. The rest of TDEE comes from physical activity, including both structured exercise and non-exercise activity thermogenesis (NEAT), which includes daily activities like fidgeting and walking.
To get an estimate of how many calories you burn each day, you need to add an activity factor to the BMR equation. Determine what activity level you fall into and multiply your BMR by the correlating number indicated.
Sedentary
You participate in light physical activity in day-to-day life, like walking up and down stairs and light cleaning.
For men: BMR x 1.00
For women: BMR x 1.00
Low Active
In addition to the light physical activity you do in day-to-day life, you also walk for 30 to 60 minutes per day at a speed that leaves you feeling slightly out of breath.
For men: BMR x 1.11
For women: BMR x 1.12
Active
In addition to the light physical activity you do in day-to-day life, you also do 60 minutes of at least moderate intensity physical activity daily. Moderate activity may include walking very briskly, cleaning heavily (washing windows or mopping) or bicycling at a light effort.
For men: BMR x 1.25
For women: BMR x 1.27
Very Active
In addition to the light physical activity you do in day-to-day life, you also do 60 minutes of at least moderate to vigorous intensity physical activity daily. Vigorous activity may include jogging, hiking or bicycling at a fast pace.
For men: BMR x 1.48
For women: BMR x 1.45
So, say our 35-year-old, 165-pound, 5-foot 7-inch person from above considered their activity levels to be active ...
For men, the estimated total daily energy expenditure would be 2,055 calories.
For women, the estimated total daily energy expenditure would be 1,877 calories.
Read More: This Is How Often You Should Exercise Each Week, According to the World Health Organization
Using BMR for Weight Loss
Once you know how many calories you burn in a day, you can use this number to figure out how many calories to eat each day based on your goals. Keep in mind that these numbers are estimates and not a perfect science. In general, if you eat about the same number of calories as you burn each day, your weight will stay the same. If you are trying to lose weight, you need to create a calorie deficit, which can be done by eating fewer calories, increasing the number of calories you burn, or both.
Research shows that the most effective way to create a calorie deficit for weight loss is to focus on eating fewer calories, not trying to burn more calories. That's because 60 to 70% of the calories you burn each day are from your BMR, which is largely determined by factors outside of your control like age, gender and genetics. Exercise makes up a small portion of the total calories burned each day, so it's more effective and sustainable to focus on dietary changes. This isn't to say you should not exercise. Exercise has many other health benefits, and diet and exercise together are proven to be the most effective for not only losing weight but also maintaining weight loss.
To create a calorie deficit by eating fewer calories, take your daily calorie needs (the total number of calories you burn each day from the final equation above) and subtract 200 to 400 from this number to obtain the number of calories needed each day for weight loss. While you may be tempted to cut more calories, remember that it will be hard to sustain. A small calorie deficit over time will lead to a weight loss of about 1/2 to 1 pound per week and will be easier for you to keep up with over time.
Can You Boost Metabolism? And If Yes, How?
Boosting metabolism refers to increasing the total number of calories your body burns each day. There are a lot of products that boast claims of boosting metabolism, from teas to supplements to herbs. However, most of these have little to no effect on increasing BMR. As mentioned above, BMR is mostly determined by age, gender and genetics. However, there are some proven ways to increase it.
Lift Weights
The more muscle you have, the more calories your body burns at rest. That's because muscle is metabolically active, meaning it burns calories. Studies show that strength training can increase RMR by as much as 7%. So if you're looking for one of the best ways to boost your metabolism (i.e., burn more calories every day), add strength training to your workout routine two to four times per week. Not only will you burn calories during the workout, but your body will continue burning calories for 12 to 24 hours following the workout. In addition, you will start burning more calories at rest (read: while you're sitting at your desk) because you will have more muscle mass.
Eat More Protein
Remember the thermic effect of food (TEF) mentioned above? Your body burns calories digesting food, and it burns more calories digesting protein than carbohydrates or fat. In fact, studies suggest the body may burn twice as many calories digesting protein compared to carbs. In addition, protein promotes satiety—helping you feel full and eat less—so if your goal is weight loss or maintenance, prioritize protein at every meal.
Other Ways to Boost Metabolism
Some research shows that spicy foods, cold water, coffee and tea may slightly boost metabolism, but the evidence isn't strong enough to suggest you should spend your energy on these solutions.
Along with increasing BMR, you can increase TDEE by adding more activity to your day—take the stairs instead of the elevator, schedule a 15-minute walk during the day, go to a spinning class or get off the train one stop early. These are all ways to increase your daily movement and therefore your daily calorie burn.
Preventing a Slow Metabolism
In the same way you can boost your metabolism, it is also possible to slow your metabolism (not something most of us are seeking!). The No. 1 culprit for slowing metabolism is crash dieting—or slashing your calories by too much and losing weight too quickly. As you lose weight, the number of calories you need each day decreases because smaller bodies do not require as much energy as larger bodies. When you lose too much weight too quickly (more than 1/2 pound to 2 pounds per week), you lower your metabolism, not only because you weigh less, but also because your body may be losing muscle. Remember that muscle burns calories for you so the less muscle you have, the fewer calories you burn and the slower your metabolism. This is why it is crucial to create a small calorie deficit through diet and combine it with daily activity and strength training.
The Bottom Line
Calculating your metabolism can give you a good idea of where your energy needs may land. However, it's always best to let your hunger and fullness cues, more than a specific calorie number, guide how much you eat . And remember that energy needs change daily. If you're sick, moving around more or are running on less sleep than normal, your energy needs increase. And if it's weight loss you're after, slow and steady wins the race, so stick with small calorie deficits over time to see healthy lasting results.
