Basal metabolic rate, or BMR, is the minimum amount of energy (calories) needed to keep the body’s vital functions going. This includes breathing, digestion, circulation, and all other functions that happen without you thinking about it.
BMR is just a number you need to know if you’re trying to lose weight. Weight loss mainly depends on calories, those you eat versus those you burn.
The total calories burned in a day is called Total Daily Energy Expenditure, or TDEE. BMR is one part of the TDEE.
If someone can raise their BMR and thus boost their total daily energy use, they can burn more calories and control their weight better.
In this article, we’ll learn how to calculate BMR, what affects it, and how to change it to meet your goals.
How to calculate Basal Metabolic Rate (BMR)
There are several formulas to calculate BMR, and you can easily use an online calculator. The formulas differ for men and women and have been updated since they were first created.
There is a common formula many experts use to calculate Basal Metabolic Rate, which is the modified Harris-Benedict formula. So, grab a calculator and see what you get.
Here are the Harris-Benedict equations to calculate Basal Metabolic Rate BMR:
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For men: (88.4 + 13.4 × weight in kilograms) + (4.8 × height in centimeters) - (5.68 × age).
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For women: (447.6 + 9.25 × weight in kilograms) + (3.10 × height in centimeters) - (4.33 × age).
When using these formulas, weight must be in kilograms and height in centimeters. For example, if a woman is 40 years old, 165 cm tall, and weighs 70 kg, you use these numbers in the equation like this:
(447.6 + 9.25 × 70) + (3.10 × 165) - (4.33 × 40) = 1433.4 is the amount of calories the body needs daily to burn just to stay alive (to do vital functions).
Online calculators
You can also use online calculators to figure out your basal metabolic rate BMR. Usually, these calculators ask for gender, height, weight, and age to estimate your BMR.
Basal Metabolic Rate BMR vs Resting Metabolic Rate RMR
BMR and RMR are different measures. As the name suggests, RMR is how many calories your body burns at rest, while BMR is how many calories it burns just to exist.
People often use these terms interchangeably, but BMR is more accurate.
To measure BMR in labs, the test is done in a dark room after 8 hours of sleep and 12 hours of fasting to make sure the digestive system is not too active. Measuring RMR is much less strict.
Factors Affecting Basal Metabolic Rate BMR
Some things can temporarily change your BMR, like eating spicy food or being in cold weather. But some factors can affect your BMR in the long run.
Factors that affect the basal metabolic rate BMR include:-
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Age: BMR usually decreases with age. So many people need to adjust their diet as they get older to avoid gaining weight.
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Weight: Heavier people have a higher basal metabolic rate.
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Height: Taller people likely have more mass, which raises their BMR. Height also helps compare muscle mass versus fat mass in the body, which also affects BMR by increasing it.
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GenderMen usually have a higher basal metabolic rate than women because of more muscle mass and bone density.
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GeneticsFactors may affect a person's basal metabolic rate, and these are factors we can't control or calculate.
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Body composition: Muscle mass uses more energy than fat mass, so the more muscle compared to fat, the higher the basal metabolic rate.
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MenopauseIf a woman is going through or has gone through menopause, she probably knows her basal metabolic rate usually drops during this time.
Changing Basal Metabolic Rate BMR
Body composition can be changed with weight training, especially high-intensity interval training HIIT which can change the basal metabolic rate.
Basal metabolic rate goes up during exercise and shortly after, but this doesn't last long. Building muscle can also raise basal metabolic rate somewhat. Also, some foods can raise it a bit. But these effects are small compared to other factors.
The best way for someone to change their basal metabolic rate is to increase activity level, which raises active metabolic rate AMR, the total calories burned daily.
You can estimate a person's active metabolic rate AMR by multiplying their basal metabolic rate BMR by a factor from 1.2 if not active to 1.9 if very active.
Formulas to calculate active metabolic rate AMR:
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Person with low activity (No exercise or very little exercise), then Active Metabolic Rate = Basal Metabolic Rate × 1.2
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The person is slightly active (Exercises 1-3 days per week), then Active Metabolic Rate = Basal Metabolic Rate × 1.375
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The person is moderately active (Exercises 3-5 days per week), then Active Metabolic Rate = Basal Metabolic Rate × 1.55
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The person is active (Exercises 6-7 days per week), then Active Metabolic Rate = Basal Metabolic Rate × 1.725
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The person is very active (Does intense exercise 6-7 days a week), then active metabolism rate = basal metabolic rate × 1.9.
For example, in the case above when calculating the basal metabolic rate, the active metabolism rate for this woman if she is low active is 1433 × 1.2 = 1719.6 calories, and if she is very active it's 1433 × 1.9 = 2722 calories.
Hormones responsible for determining basal metabolic rate BMR
The basal metabolic rate is mainly determined by thyroid hormones TSH. Thyroid hormones T3 and T4 bind to mitochondrial receptors, which increases ATP production and glucose usage.
ATP helps transfer and use energy, these effects lead to an increase in the cell's basal metabolic rate.
Good basal metabolic rate BMR
Basal metabolic rate BMR is neither (good) nor (bad), really it’s just info that can be used to understand a person's health condition and set weight goals and plans.
If someone wants to lose weight, they can work on lowering the basal metabolic rate, along with adjusting calorie intake to create a calorie deficit.
If someone wants to gain weight, the basal metabolic rate helps to understand the minimum calories the body needs, so they can consume more than that.
In the end, the BMR helps to better understand the body's daily calorie needs. But keep in mind it's just an estimate. To change body composition by losing or gaining weight, you need to consider BMR and activity levels. Also, some factors you can't control affect BMR and calorie burning.
