What Is Basal Metabolic Rate (BMR)?
Even on your rest days, your body burns energy as it keeps all your vital processes fully functioning. The amount of energy used by your body at rest is known as your basal metabolic rate or resting energy expenditure.
Basal metabolic rate (BMR) accounts for about 65-70 percent of total energy expenditure in adults, and it can vary due to many factors. BMR can be used as a tool to help determine your total energy requirements, factoring in your daily activities and exercise. A healthy, balanced diet will need to include meal portions that provide your total energy for each day.
What is basal metabolic rate?
Basal metabolic rate (BMR) is the amount of energy your body uses to stay alive, at rest.
Another way of thinking of this is your “baseline metabolism” — the amount of energy, in calories, that your body uses to keep you breathing and keep your organs functioning, if you were to do nothing but lie down, in a controlled environment, for a 24 hour period.
Basal metabolic rate varies from individual to individual. BMR is commonly calculated using an approximate formula for resting metabolic rate, however a 2015 literature review by the University of North Carolina and published in Medicine and Science in Sports and Exercise, found that resting metabolic rate can vary by as much as 20-30 percent between different demographics.
Factors affecting your BMR
Your basal metabolic rate depends on a variety of factors and this means that it may change over time in response to lifestyle, environmental, emotional or life-stage changes.
Temperature of the environment
When the temperature of the environment is very high or very low, the body requires more energy to maintain ideal core body temperature.
When the body is under stress, cortisol and other hormones are released. These hormones act to prepare your body for “fight-or-flight” by increasing your heart rate, directing blood flow to the muscles and tensing muscle tissue — burning additional energy in the process.
Crash dieting or fasting
Eating too few calories can encourage the body to burn less energy, reducing BMR by up to 15 percent.
Stimulants and medication
Stimulants such as caffeine or nicotine can increase the basal metabolic rate.
Disease, injury or infection
When you have an injury or illness, the body uses energy to build new tissues and create an immune response.
Larger adult bodies have more tissue that requires greater energy expenditure to sustain, resulting in a higher basal metabolic rate.
Lean muscle burns energy rapidly, even at rest. By comparison, adipose (fat) tissue uses much less energy than other organs and tissues of the body.
This means that exercise that promotes lean muscle growth, such as strength training, can help to increase BMR by increasing overall lean muscle mass.
Gender and age
Basal metabolic rate is calculated differently for men and women, and it tends to decline with age.
What and when you eat
It takes energy to digest meals and snacks, so after eating you will burn some energy in order to digest the macronutrients from food. Eating protein will raise the BMR by 20-30 percent, while eating carbohydrates raises BMR 5-10 percent. Spicy foods can also cause the body to increase energy expenditure.
Nutritional deficiencies, in particular low iodine, may act to slow down the metabolism.
How to calculate BMR
The only way to accurately calculate your BMR is to directly measure it using specific laboratory equipment. However, your BMR can be estimated using the following equation for resting energy expenditure.
A 1990 study by the University of Nevada, published in the American Journal For Clinical Nutrition, proposed the now widely adopted Mifflin-St Jeor equation, where the BMR for women within a healthy normal-weight and moderately overweight range is:
BMR (calories) = 10 x weight (kg) + 6.25 x height (cm) - 5 x age (y) - 161
It is important to remember that this equation will provide only a rough estimate of your BMR, and should be used as a guide only. Due to the demographics of the original study, which was based in the US, more research is required to confirm if this equation also applies to populations from different ethnic or geographic backgrounds.
Does your energy expenditure increase with exercise?
According to the World Health Organisation, an individual with a sedentary lifestyle will expend about 1.53 times their BMR, in calories, in the course of daily activities. However, if you do vigorous exercise this energy expenditure of calories can increase to around 2.25 times BMR or higher for 3-48 hours after the exercise session is complete.
During periods of intense and prolonged exercise, total energy expenditure can increase by as much as 4.5-4.7 times BMR, and remain elevated for a prolonged period once exercise is ceased.
In particular, high-intensity resistance training can effectively increase BMR. A 2000 study in women age 22-35, published by Colorado State University in the International Journal of Sport, Nutrition, Exercise and Metabolism, found that resting metabolic rate increased by after intense resistance training, and remained elevated for 16 hours after exercising.
Does BMR determine whether you will gain weight?
A 2016 study conducted by the Mayo Clinic and published in the American Journal Of Clinical Nutrition found that BMR alone was not a predictive indicator of weight gain.
The researchers found that adults with a low BMR did not gain more weight than adults with a high BMR, and concluded that habitual differences in food intake and activity levels of individuals counter the effect of the basal metabolic rate on weight gain in a Western population.
Knowing your basal metabolic rate can help you plan your nutrition
One way that BMR is used is to calculate your daily nutrition requirements. Understanding your BMR can help guide you when planning meals and snacks, to ensure that you meet your energy requirements each day.
However, healthy eating requires more than eating enough calories each day. It’s important to take a balanced approach to nutrition, ensuring you are eating enough macronutrients and micronutrients to fuel your body.
Including a variety of foods each day will ensure that you also promote muscle recovery, good digestion and overall good health.
* Results may vary. Strict adherence to the nutrition and exercise guide are required for best results.