What is BMR and How Can it Help Your Weight Loss Journey?

When it comes to trimming fat, there is a simple roadmap to follow: burn more calories than you consume. To determine how many calories you burn in a day, you must first know what your basal metabolic rate (BMR) is. We will explain what BMR is, how you can calculate it and the role it plays in your health goals.

What does BMR stand for?

BMR is an acronym to describe basal metabolic rate, or the energy (calories) your body needs to perform basic functions such as breathing, blood circulation, cellular growth, body temperature regulation, hair growth and hormone production. 

Many people get confused with BMR and activity levels, but BMR only has to do with essential bodily functions. In other words, BMR only includes what your body does at rest.

Basal metabolic rate is just one aspect of metabolism, the process of converting solid and liquid foods into energy. Every time you eat, food mixes with oxygen to provide energy. Although you may only eat three times a day, your body’s metabolic activity is a 24/7 process.

In addition to BMR, your metabolism also includes calories burned during daily activities and calories burned during exercise. Together, these factors add up to your total energy expenditure. Here is a brief overview:

Resting calories: About 70 to 80 percent of calories burned occur as part of your basal metabolic rate. This includes sleeping, when the body can burn about 50 calories per hour.

Thermal effect of food: It takes energy to digest food. About 10 percent of your daily caloric expenditure comes from breaking down and storing the food you eat.

Activity calories: This includes any calories burned not exercising. It is also called nonexercise activity thermogenesis (NEAT) and includes everything from brushing your teeth to walking to the kitchen to fix lunch. You can burn anywhere from 100 to 800 calories depending on what you do each day.

Exercise calories: As the name suggests, these are the calories burned when working out, such as walking, biking, running or strength training.

BMR vs RMR?

Some people confuse basal metabolic rate with resting metabolic rate. While similar, BMR describes the calories needed to carry out necessary functions at rest, and RMR (also called resting energy expenditure) is the actual number of calories burned while at rest. RMR includes low-energy activities such as going to the bathroom or fixing a sandwich for lunch.

To calculate RMR, oxygen intake and carbon dioxide output is measured after you’re sitting or lying down for 15 minutes and haven’t exercised that day.

In general, your BMR will be lower than your RMR since RMR accounts for low-effort tasks in addition to carrying out necessary bodily functions. BMR is a way to measure how many calories your body needs each day to perform basic functions. By contrast, RMR is a better tool to gauge how many calories you burn each day without exercise.

What impacts BMR?

Each person’s BMR is based on a variety of factors, some of which you can control (body composition) and others you can’t control (age, gender, hormones).

• Age: BMR and age are inversely related – children have a higher BMR compared to older adults who have a lower BMR. In general, the older you get, the less muscle mass you have. As a result, BMR decreases.
• Body composition: Muscle needs more energy than fat (fatty tissue doesn’t require as much energy), so people with more muscle mass and a lower body fat percentage have a higher BMR.
• Body shape: People with a larger body surface (tall and thin) area have a higher BMR. People who are shorter and weigh more have a lower BMR.
• Gender: Men usually are taller and have more muscle mass than women, which leads to a higher BMR.
• Hormones: Thyroxine, a hormone produced by the thyroid, controls how much energy your body uses. People with higher levels of thyroxine have a higher BMR.

What can BMR help with?

The calories your body needs during an inactive stage may not seem like important information, but BMR is helpful for many reasons.

For starters, it helps you understand your calories needs and goals regardless of if you’re dieting. At a baseline, knowing your BMR provides a caloric goal your body needs to perform basic functions. For example, a BMR of 1,500 means you need to consume at least 1,500 calories to help your body work efficiently. This knowledge is important if you plan to gain, lose or remain the same weight.

If you plan on dieting, BMR also acts as your starting point to know how many calories you need to consume and burn to lose weight. For example, if your BMR is 1,700, you burn an additional 300 calories doing low-energy tasks and go for a run that burns an extra 250 calories, you know 2,250 calories is your break-even number for the day. Eating anything fewer than 2,250 calories will help you lose weight in what is called a negative energy balance – the difference between the energy you take in (calories in) and the energy you burn (calories out).

Finally, BMR can help you track strength and muscle growth. BMR can increase as muscle mass increases and fatty tissue decreases.

What is a good BMR?

Each person’s BMR is unique to them and shouldn’t be compared. Therefore, there isn’t a good BMR or a bad BMR. Even people who are the same age, sex, height, weight and body composition can have BMRs that vary by as much as 10 percent. Factors such as genetics or even organ size – some people have large organs, which require more energy to function – account for these differences.

Typically, BMR is between 1,000 and 2,000, meaning you need 1,000 to 2,000 calories to fuel basic functions. BMR for women average around 1,400, while BMR for men average between 1,600 and 1,800.

BMR calculator

There are two types of equations that serve as a way to calculate your BMR – the Miffin St Jeor equation and the Harris Benedict equation.

The Mifflin St Jeor is a newer and more accurate formula that also adds your weight and height then subtracts it by your age plus a preset number – 161 for females and 5 for males.

The Harris Benedict equation dates back to 1919. This equation takes a preset number – 655.1 for females and 66.47 for males – and adds your weight and height and subtracts your age.

Here is an example using both formulas: A 20-year-old male who weighs 180 pounds and is 6-foot tall would have a BMR of:

• Miffin St Jeor: BMR = (10 x 81.6466 = 816.466) + (6.25 x 182.88 = 1,143) - (20 x 5 = 100) + 5 = 1,864.466
• Harris Benedict: BMR = 66.47 + (13.75 × 81.6466 = 1,122.64 ) + (5.003 × 182.88 = 914.95) − (6.755 × 20 = 135.1) = 1,968.96

As you can see, the Miffin St Jeor equation gives you a total calorie output of 1,864. This means your body will burn 1,864 calories if you lay in bed all day.

Using the same equation, an 80-year-old man who is the same height and weight will have a BMR of 1,564 when adjusted for age. The difference of 300 calories explains why many older people don’t eat as much because they don’t need as many calories per day.

Can you increase BMR?

While there are several uncontrollable factors that play a role in BMR such as age, sex, height and genetics, alterations to your body composition may slightly increase your BMR. However, any changes to BMR will be minimal and require strenuous resistance training.

Lean muscle mass burns more calories than fat – 6 calories per pound compared to around 2 calories per pound. That means the more muscle you have, the higher your BMR will be. Using simple math, you can increase your BMR by about 30 calories if you add 5 pounds of muscle.

Talk to your primary care physician if you want to learn more about your basal metabolic rate and the role it plays in your metabolism. For more healthy eating tips, visit the INTEGRIS Health For You blog.