Why Your Resting Metabolic Rate (RMR) Matters

January 20, 2021 Fitnescity, Inc

Understanding your unique RMR gives you the power to make more efficient and data-driven lifestyle choices.

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Your resting metabolic rate (RMR) is the number of calories your body burns when completely at rest. Even as you lounge by the pool, relax on the couch watching Netflix, or even sleep, your body is performing basic, life-sustaining functions like breathing, cell growth and repair, and blood circulation. The amount of energy or number of calories that your body expends to sustain these vital organ functions is your RMR.

Here, we discuss RMR in more detail, including its impact on your metabolism, determining factors, and the importance of knowing your unique rate.

How your resting metabolic rate influences your metabolism

In a nutshell, your metabolism is all the chemical processes that your body needs to stay alive. It dictates the number of calories you burn each day. A calorie is a unit that measures the energy you get from the food you consume and the energy you expend through physical activity. The faster your metabolism, the higher your daily calorie burn.

The following factors impact your metabolic speed:

Resting metabolic rate: This is the number of calories you burn when your body is in a state of complete rest. Put another way, your RMR is the minimum number of calories you need to keep your body functioning properly.
Thermic effect of food (TEF): Your thermic effect of food refers to the number of calories you burn through digesting food and absorbing nutrients. Your TEF typically accounts for 10 percent of the total calories you burn each day.
Exercise activity thermogenesis (EAT): EAT is the number of calories you burn each day through physical exercise.
Non-exercise activity thermogenesis (NEAT): NEAT refers to the number of calories you burn through non-exercise activities, like typing on your computer, driving your car, or standing up.

Of these four factors, your RMR has the biggest impact on your total daily energy expenditure (TDEE), accounting for around 70 percent of the total number of calories you burn per day. It’s followed by your NEAT (as much as 15 percent of your TDEE), your TEF (around 10 percent), and EAT (around 5 percent).

What factors influence your resting metabolic rate?

Everyone’s resting metabolic rate is different. Your resting metabolic rate is influenced by various factors, including:

Age. As you age, your resting metabolic rate decreases almost linearly. Metabolic rate is estimated to decrease by around 1-2 percent per decade.
Height and weight. Larger and/or taller bodies with higher amounts of lean muscle tissue and/or body fat tend to burn more calories. This is because bigger bodies have to work harder to support and maintain additional weight.
Body composition. Because muscle requires more energy to maintain than subcutaneous or visceral fat, you tend to burn more calories if you have a higher proportion of lean body mass.
Gender. Because men tend to have a higher body mass, their metabolism is typically higher compared to women. And because of higher amounts of testosterone, men typically have more muscle mass, which requires more energy to maintain.
Hormones. Hormonal imbalances, like hypo- and hyperthyroidism, can impact your metabolism. Similarly, during the luteal phase of a woman’s menstrual cycle—which begins after ovulation and ends before the start of the period—resting metabolism is thought to increase as much as 5 percent.
Genetics. Some people are born with faster metabolisms, while others are born with genetic disorders that can impact RMR.
Medication. Both prescription and over-the-counter medications can result in an increase or decrease in your metabolism.
Calorie restriction. Restrictive diets that force your body into starvation mode can result in a sharp decline in your RMR as your metabolism slows to preserve energy.
Stress or excitement. Both stress and excitement can raise your RMR due to an increase in heart and respiration rate.
Environment. Cold or hot weather can force the body to work hard to maintain its normal temperature, thus increasing your RMR.

Why you should know your resting metabolic rate

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Impacted by a wide range of factors, resting metabolic rate can vary vastly from person to person, even among those of the same gender, age, and weight range. Knowing your unique RMR can help you understand the number of calories you need to consume each day to achieve weight optimization and your overall health goals.

For example, let’s say you determine your RMR to be 1,800 per day. Let’s also say that every day, you work out for an hour and burn 500 calories. If you add these caloric values together, you’ll get a figure that roughly represents the number of calories you burn per day: 2,300.

To maintain your weight in this scenario, you would need to consume 2,300 calories per day. To lose one pound, you would need to burn around 3,500 calories more calories than you eat. To do this in a week, then, you would need to adjust your food consumption so you’re taking in around 500 fewer calories (1,800 calories per day). To gain weight, you would need to eat around 500 more (2,800 calories per day).

The bottom line: Knowing your unique RMR lets you make more efficient, data-driven and educated choices about your nutrition, exercise and lifestyle.

How to find out your resting metabolic rate

You’ll find plenty of resting metabolic rate calculators across the internet. These calculators typically factor in your age, gender, height, and weight to come up with a rough estimate of your RMR. Alternatively, you can get a general idea of your RMR with the following formula known as the Mifflin-ST Jeor equation:

Men: 10 x weight (kg) + 6.25 x height (cm) – 5 x age + 5 = RMR
Women: 10 x weight (kg) + 6.25 x height (cm) – 5 x age – 161 = RMR

However, it’s important to understand the limitations of these estimates. Because your RMR is influenced by a wide range of factors beyond your age, weight, height, and gender, relying on general RMR calculators or formulaic estimates can put you off track by hundreds of calories.

The most accurate way to determine your resting metabolic rate is through a Resting Metabolic Rate test. These tests accurately assess the number of calories your body burns at rest using an advanced metabolic cart that measures your expired oxygen (O2) and carbon dioxide (CO2) values. During the test, you typically sit or lay in a relaxed position and breathe into a hood, mask, or mouthpiece as the test measures the amount of CO2 you exhale.

With your O2 and CO2 values, the technician can assess the number of calories you expend at rest. This number is then projected out into 24 hours to tell you a highly accurate estimate of calories you expend in one day without performing any activities.

Your RMR test results also reveal your respiratory exchange ratio (RER), or the ratio between the volume of CO2 your body produces and the amount of O2 it consumes. Your RER lets you know whether your body burns more fat or carbohydrates for energy.

A resting RER of .70 indicates your primary energy source is fat, while an RER of .85 shows you rely on a combination of fat and carbohydrates. A resting RER of 1.00 means your primary energy source is carbohydrates. Ideally, your body at rest should have an RER between .70 and .85, indicating it relies more on fat than carbohydrates. Burning more fat at rest means you preserve carbohydrates for brain function and intense physical activity.

How often to test your resting metabolic rate

Because your RMR is a dynamic number impacted by factors listed above—like your age or changes in your body composition, diet, or medication—it’s a good idea to test yours every three to six months. Because your unique resting metabolic rate informs your nutritional consumption and exercise needs, knowing your current RMR tells you the precise number of calories you need to gain, maintain, or lose weight.

When you follow a fitness or nutrition program, your body’s calorie demands may change. If you are trying to lose weight and you hit a plateau, you may find upon retesting your RMR that your daily caloric needs have gone down. Alternatively, if you are following a fitness plan that increases your lean muscle mass, you may learn your RMR has increased. An up-to-date RMR can help you manage your daily food intake and make smart choices about exercise based on your personal goals.

Learn more about RMR testing or get started now by finding a partner location near you.

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