BMR (Basal Metabolic Rate)

What is basal metabolic rate (BMR)?

Your basal metabolic rate (BMR) refers to the minimum number of calories your body needs to function at a basic level. This includes maintaining all your cells and essential bodily functions, like breathing, blood circulation and body temperature. BMR varies from person to person based on several factors.

Your BMR is your body’s major source of energy expenditure. It fulfills 60% to 70% of the total energy your body uses. Your body uses about 10% of its total energy to process food into fuel. The remaining energy fuels your physical movement.

You may want to learn more about BMR to help manage your weight. It can help provide a general understanding of what your body needs to function. But know that your BMR is just one piece of the puzzle when it comes to weight management and calorie usage.

What factors affect my basal metabolic rate?

Several factors influence your basal metabolic rate, including:

• Body size. The more body tissue and cells you have, the more energy your body requires to maintain them.
• Amount of lean muscle tissue. Muscle tissue requires a lot of energy to maintain itself.
• Amount of adipose tissue (body fat). Compared to muscle tissue, fat cells require less energy to maintain themselves, but they require energy, nonetheless.
• Sex. People assigned male at birth (AMAB) generally have a faster BMR because they’re generally larger than people assigned female at birth (AFAB). People AMAB also tend to have more lean muscle mass due to higher testosterone levels.
• Age. Your BMR decreases with age mainly due to a loss of muscle mass. But hormonal and neurological changes can also affect your BMR as you age.
• Race. Your race and/or ethnicity may affect your BMR. Researchers are still studying this.
• Genetics. Your genes likely influence your BMR. Researchers are still studying how genetics affect metabolism.

Temporary situations that can affect your BMR include:

• Skipping meals, fasting or starvation. Thanks to evolution, your body is always trying to protect itself from losing weight. If you consume too few calories, your body will slow down your BMR.
• Environmental temperature: If you’re in a very cold or very warm environment, your body must work harder to maintain a healthy body temperature (like through shivering or sweating). These scenarios increase your BMR.
• Thyroid hormone levels. Elevated thyroid hormone levels (hyperthyroidism) increase your BMR. Low thyroid hormone levels (hypothyroidism) decrease your BMR.
• Illness or injury. When you’re sick or hurt, your BMR increases because your body is busy fighting off an infection and/or repairing tissues.
• Stimulants. Stimulants like caffeine, nicotine and amphetamines can increase your BMR.

Life stages that affect your BMR include:

• Growth. Infants and children require more energy to actively build tissue as they grow.
• Pregnancy. Your BMR increases during pregnancy due to an increase in body mass and the energy that’s required to grow a fetus.
• Lactation. Your body requires more energy to make breast milk (chest milk). Studies show there’s a 15% to 25% increase in energy expenditure for milk production.
• Menopause. Hormone changes in menopause lead to a decrease in lean muscle mass. This typically decreases your BMR.

What is a normal basal metabolic rate?

There’s no such thing as “normal” when it comes to basal metabolic rates. Each person has a BMR unique to their body based on various factors. Scientists can only provide averages when it comes to BMR.

The average person AMAB has a BMR of around 1,696 calories (7,100 kilojoules) per day. The average person AFAB has a BMR of around 1,410 calories (5,900 kilojoules) per day. These estimates may change based on your race and/or ethnicity.

It’s important to remember that this energy (calorie) expenditure only involves the energy your body needs to maintain its basic functioning. These numbers don’t include the calories your body needs to turn food into energy and for physical activity.

If you have questions about how many calories you should consume in a day, it’s best to talk to your healthcare provider or a registered dietitian. They can help you calculate a realistic number based on your unique circumstances.

How do I calculate my BMR?

It’s most accurate to measure your BMR in a lab setting under very strict conditions. More specifically, an expert would calculate your BMR while you’re:

• At complete rest.
• Mentally and physically calm.
• In an awake state after sleep, 12 to 14 hours after the last meal you ate.
• In a room at a comfortable temperature (thermally neutral to your body temperature).

Because most people don’t have access to this kind of testing, scientists have developed equations to estimate your BMR. The most commonly used equation is called the Harris-Benedict equation:

• For people assigned male at birth: BMR = 88.362 + (13.397 x weight in kilograms) + (4.799 x height in centimeters) - (5.677 x age in years).
• For people assigned female at birth: BMR = 447.593 + (9.247 x weight in kilograms) + (3.098 x height in centimeters) - (4.330 x age in years).

Resting metabolic rate calculations

You may see or hear about resting metabolic rate (RMR) calculations. RMR and BMR are similar but different. RMR represents the amount of energy your body needs to function while at rest. But it includes the calories necessary for low-effort daily activities like going to the bathroom and getting dressed. RMR is slightly higher than BMR by about 10% due to the calorie needs of these low-energy activities.

Equations to estimate RMR include:

• For people AMAB: RMR = (4.38 x weight in pounds) + (14.55 x height in inches) - (5.08 x age in years) + 260.
• For people AFAB: RMR = (3.35 x weight in pounds) + (15.42 x height in inches) - (2.31 x age in years) + 43.

How can I increase my BMR?

In many ways, there’s not much you can do to change your BMR. You can’t alter several factors that contribute to your BMR, like your genetics, age and height. One healthy way to increase your BMR is to build lean muscle mass. This increases your BMR because lean muscle tissue requires significant energy to maintain its structure.

Incorporating regular resistance training and strength-training exercises into your routine (which are different from aerobic exercise) can help build lean muscle. Examples of these types of exercise include lifting weights, Pilates and kettlebell training.

Having a very fast metabolism (BMR) isn’t always a good thing. For example, a condition called hypermetabolism can happen when someone has a serious illness, like cancer. Also, things like hyperthyroidism or taking certain stimulants can make your metabolism faster, but they can also be harmful to your health.

If you have questions or concerns about your metabolism and how it affects your weight and health, reach out to your healthcare provider.