What is basal metabolic rate? How calculating your BMR can help you lose weight

• Basal metabolic rate (BMR) accounts for about 60% of the calories you burn each day.
• To calculate your BMR, you should use the Mifflin-St. Jeor equation, which is the most accurate.
• Knowing your BMR can help you determine how many calories you should eat a day to lose weight.

Your basal metabolic rate (BMR) refers to the amount of energy - or the number of calories - your body needs at rest to perform basic functions like breathing and pumping blood.

Note: BMR is often used interchangeably with RMR, or resting metabolic rate. Technically BMR is only measured in a dark room after eight hours of sleep and 12 hours of fasting.

BMR accounts for about 60% of the total calories you burn each day. But it does not include calories needed for physical activity like exercising, walking, or even just brushing your teeth.

Knowing how to calculate your BMR can help you better understand how many calories you need to eat each day to maintain or lose weight. Here's how to calculate BMR and tips to increase it.

How to calculate BMR

BMR can vary based on several factors, and may even fluctuate throughout your life, says Dimitar Marinov, MD, an assistant professor at the Medical University of Varna, Bulgaria.

Factors that affect BMR include:

• Age
• Sex
• Weight
• Body composition, which is how much fat or muscle you have on your body
• Genetics

There are two commonly used equations to calculate BMR:

1. Harris-Benedict equation
2. Mifflin-St. Jeor equation

The Mifflin-St. Jeor equation is considered more accurate and is more widely used, Marinov says.

You can use an online calculator to determine your BMR using the Mifflin-St. Jeor equation or do the equation yourself.

Mifflin-St. Jeor equation for men and women

• Men: (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) + 5
• Women: (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) - 161

How to use BMR to lose weight

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Understanding your BMR is an important starting point to making a weight loss plan because it enables you to determine your overall energy expenditure and how many calories you need to remain in a calorie deficit, says Alex Rothstein, the coordinator of the Exercise Science program at the New York Institute of Technology.

Important: Consuming fewer calories than your BMR may actually cause you to hang on to extra weight, Rothstein says. It may slow your metabolism and put you at risk of starvation mode, which is when your body conserves energy and fat, making it difficult to lose weight.

If you are trying to lose weight, Rothstein recommends, "eating at least as many calories as your estimated BMR and increasing calorie expenditure with increased exercise and daily activity."

How much weight you should aim to lose will vary depending on the individual, but experts recommend losing weight at 0.5% to 1% of your body weight every week. For a 180 pound person with a goal weight of 140 pounds, it would take 25 to 50 weeks to hit that point:

How to increase BMR

Your BMR is based on several factors that are out of your control, like your age and sex. But you can change your body composition by building more muscle, which may slightly increase your BMR.

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Muscle burns more calories than fat, so the more muscle mass you have, the more energy your body needs to maintain it, Marinov says. Strength or resistance training can help build muscle by stimulating muscle growth.

Exactly how much muscle you would need to increase your BMR depends on several individual factors, but in general, one pound of muscle burns about 6 calories a day, which is about three times the calories burned by a pound of fat. So, putting on about 10 pounds of muscle could increase your BMR by about 60 calories.

A 2012 review found several weeks of resistance training may increase resting metabolic rate by as much as 7%. Meanwhile, in a small 2014 study, nine months of resistance training increased participants' BMR by about 5%.

While it is possible to slightly increase your BMR by building muscle, the best way to burn more calories in the day is through regular exercise, whether that be strength training, cardio, or a combination of the two, Marinov says.

Insider's takeaway

BMR is the number of calories your body needs every day to perform basic functions. BMR can vary based on several different factors, including age, weight, sex, body composition, and genetics.

You may be able to slightly increase your BMR by building muscle, but you should consult with your doctor before beginning any strength training regimen.

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