Boost Weight Loss by Knowing Your BMR: Here’s How

While many people blame a slow metabolism (they mean BMR) on weight gain, it’s actually true that increases in body size result in an increase in BMR, explains Tim Church, MD, PhD, chief medical officer at Wondr Health.

The majority of differences between any two people’s basal metabolic rate comes down to fat mass and free-fat mass, which includes organ size and muscle levels, writes Herman Pontzer, associate professor of evolutionary anthropology at Duke University, in an article for Scientific American. Age is also a factor, he says.

At rest, a pound of fat burns roughly two calories per day and a pound of muscle burns roughly six calories, Dr. Church says.

That’s why men naturally enjoy a higher BMR than women, as they tend to have more overall body size and lean mass levels, explains Sari Greaves, RDN, a registered dietitian-nutritionist at LBS Nutrition in East Brunswick, New Jersey, and author of Cooking Well.

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Basal Metabolic Rate (BMR) vs. Resting Metabolic Rate (RMR)

BMR and RMR are slightly different.

“BMR is the absolute minimum metabolic rate,” Church says. It is typically determined only in laboratory settings, with people undergoing measurements in a darkened, temperature-controlled room immediately after 8 hours of sleep and 12 hours of fasting and reclining, according to the American Council on Exercise.

Meanwhile, “RMR is the metabolic rate when at rest, awake, and sitting still.” RMR testing does not require a fast and may be performed later in the day. RMR is typically 10 to 20 percent higher than BMR, according to the NASM.

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Estimating Your BMR or RMR to Help With Weight Loss

Knowing your BMR or RMR can help you better determine your total daily energy expenditure in order to create a caloric deficit, defined as consuming fewer calories each day than you burn for energy. A caloric deficit is required to lose weight.

But because most people do not have access to state-of-the-art labs that are required to determine BMR, equations are often used to make approximations. The easiest way to measure your metabolic rate is to use an online calculator. You can find many calculators online, and all use varying equations.

The commonly used metabolic equation, called the Harris and Benedict equation, was first designed in 1918 (and updated in 1984). While it was intended to estimate BMR, it actually estimates RMR, according to the NASM. It uses height, weight, biological sex, and age to determine RMR and is based on average lean mass levels. The Mifflin-St Jeor equation is another equation that uses the same variables but may be more accurate, Church says.

Other metabolic equations, such the Cunningham equation, use your total levels of lean body mass, which is a primary determiner of BMR and therefore RMR. Yet using such a calculator requires you to be able to measure your body’s levels of fat versus free-fat mass, Church says. Calipers and smart scales are two popular at-home options, while the most accurate measures are performed in professional and laboratory settings.

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Below, you can see how estimated RMR varies based on the equation used.

Revised Harris-Benedict

Men: (88.40 + 13.40 x weight in kg) + (4.80 x height in cm) – (5.68 x age in years)

For example, if a man is 180 pounds, 5’11”, and 43, his RMR is 1,804 calories.

Women: (447.60 + 9.25 x weight in kg) + (3.10 x height in cm) – (4.33 x age)

For example, if a female is 130 pounds, 5’3″, and 36, her RMR is 1,333 calories.

Mifflin-St Jeor Equation

Men: (9.99 x weight in kg) + (6.25 x height in cm) – (4.92 x age in years) + 5

For example, if a male is 180 pounds, 5’11”, and 43, his RMR is 1,734 calories.

Women: (9.99 x weight in kg) + (6.25 x height in cm) – (4.92 x age in years) – 161

For example, if a female is 130 pounds, 5’3″, and 36, her RMR is 1,249 calories.

Cunningham Equation

Men and women: 500 + (22 x lean body mass in kg)

For example, if a man is 170 pounds, 5’11”, 43, and his body-fat percentage is 20 percent, his RMR is 1,857 calories.

For example, if a female 130 pounds, 5’3″, 36, and her body-fat percentage is 25 percent, her RMR is 1,473 calories.

BMR and Total Daily Energy Expenditure

BMR or RMR can be used to estimate total daily caloric expenditure. According to the American Council on Exercise, after you determine your RMR, based on one of the above equations or an online calculator, you can multiply it by one of the numbers below, called activity factors:

• Sedentary Little to no exercise, multiply by 1.2
• Lightly Active Light exercise one to three days per week, multiply by 1.375
• Moderately Active Moderate exercise on three to five days per week, multiply by 1.55
• Very Active Hard exercise six or seven days per week, multiply by 1.725
• Extremely Active Hard exercise every day and/or a physical job, multiply by 1.9

If the man in the above example exercises two days per week, his daily caloric expenditure is roughly 2,384 to 2,481 calories.

If the woman in the above example exercises six days per week, her daily caloric energy expenditure is roughly 2,155 to 2,541 calories.

This calculation gives you the estimated number of calories you burn in one day at your current level of activity; this is how many calories you need to consume per day to stay at your current weight.

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How Knowing Your BMR Can Help You Lose Weight

To lose weight, you need a caloric deficit, meaning that you either must reduce your caloric intake below your total daily energy expenditure or increase your total daily energy expenditure, says Greaves. For example, you can try multiplying your RMR by various activity factors to see how your daily caloric burn would fluctuate with increased exercise.

Another benefit of increased exercise is that it can have a small effect on both RMR and BMR. Research shows that intense exercise provides a temporary boost to your RMR, an effect sometimes referred to as afterburn, or excess post-exercise oxygen consumption (EPOC). This represents the calories that the body expends to return the body to homeostasis following exercise.

Strength training provides a more lasting boost to BMR by altering your body’s composition. As previously stated, a pound of fat burns roughly two calories per day while a pound of muscle burns six at rest, Church says. To put that into perspective, gaining two pounds of muscle will increase RMR by about 12 calories.

Additional reporting by Dennis Thompson Jr.