Basal metabolic rate BMR is one of the most reliable ways to calculate your daily calorie intake. If you want to gain muscle or lose some pounds (and following a low calorie diet), t is important to calculate your BMR to understand minimum energy that your body requires.
In this post, we explain the basal metabolic rate BMR and what factors influence it. We elaborate on the BMR calculator, Harris-Benedict equation, and other multiple formulas it uses, and how it can help you gauge your daily calorie needs (since BMR is 60% of your total daily energy expenditure).
What Is Basal Metabolic Rate BMR?
Basal metabolic rate BMR is the minimum number of calories body requires to adequately perform functions vital for survival.
Even when you’re at rest, energy generated from the metabolism (breakdown) of food is used for breathing, pumping blood (circulation), cell production, etc.
This minimum value of calories utilized at rest or BMR is obtained by BMR calculator when a person:
- Is awake, but inactive physically and completely rested mentally, i.e., not stressed or excited. This is because more calories are burned when you’re exercising or engaged in physical activities, as well as in a state of anxiety /excitement because the body is setting up a fight-or-flight response.
- In post absorptive state or fasting for 6 to 12 hours, since food intake (especially protein-rich food) increases metabolism for a few hours. This is called TEF or the thermic effect of food.
- In a comfortable environment of moderate temperature, i.e., 20 to 25°C, the rate of metabolism increases in hot weather, followed by a rapid decline at extremely high temperatures.
Being in a cold environment burns more number of calories, which is why you need a neutrally temperate environment to obtain an accurate BMR reading.
Factors Affecting Basal Metabolic Rate
Here are the major variables of BMR:
Muscle Mass and Activity Level
Higher muscle mass is associated with a high basal metabolic rate.
Muscles need the energy to contract and relax. According to research, muscles use almost 10 to 15 kcal/kg a day. This is why the body burns more number of calories in people having higher lean body mass (hence they have higher BMR).
In the case of high-intensity exercises and athletic sports, too, BMR is high because activity increases lean mass.
Activity level is generally categorized as follows:
- Little to no exercise
- Exercise 1-3 times a week
- Exercise 4-5 times a week
- Daily exercise or intense exercise 3-4 times a week
- Daily intense exercise
Note that in the above classification, exercise and intense exercise imply 15 to 30 minutes and 45 to 120 minutes of increased heart rate activity, respectively.
Gender and Body Composition
The difference in BMR between men and women has also been chalked up to variances in their lean mass and fat percentage. Men naturally have a higher BMR due to more muscle mass (consumes more energy).
In contrast, women tend to have more body fat mass. When it comes to the breakdown of food and energy production, fat cells are described as “sluggish” as they burn fewer calories than muscles and other tissues. Hence, women have low BMR.
Men have a higher rate of fat loss (thus more fat free mass) than women, and hence, they comparatively requires energy in greater amounts.
As we age, our height and lean mass reduce, whereas body fat percentage gradually increases. Moreover, hormonal changes associated with age also impact BMR.
Therefore, BMR also naturally decreases with age.
The exact mechanism by which genetics influence BMR is not yet known. However, scientific data suggests that your hereditary traits highly impact your metabolism and energy utilization.
Some people naturally have an efficient metabolism (better digestive system), and hence, they need fewer calories (thus, they have a low BMR).
A research paper reports significant differences in the BMR of individuals due to genetic variations.
Generally, people inhabiting warm areas tend to have lower BMR than those living in cold climates.
This is driven by the natural homeostatic system in the human body, which involves self-regulation of features like metabolism, heart rate, blood pressure, the diameter of veins and arteries, etc., to maintain a constant and stable internal environment.
Food intake is directly related to an increase in BMR. Understandably, starvation thus reduces BMR calorie utilization is lowered to adjust to the energy deficit.
With increased weight, the basal metabolic rate rises in pregnant women. However, nearing the term, a small drop in BMR has been noticed.
Weight and Height
Your current weight and height are important determinants of minimum number of daily calories needs or BMR, and are therefore asked in a BMR calculator. This is because, with a higher body surface, you would need more energy to function.
Apart from this, taller people also have larger organs that weigh more, which is also linked with high BMR.
Caffeine and Drugs Intake
100 mg of caffeine can increase your basal metabolism and BMR by 3% to 4%. Similarly, other factors and stimulants like nicotine, cocaine, amphetamines, etc also increase metabolism.
Certain supplements, particularly the ones used for weight loss, can raise your BMR.
What Is Resting Metabolic Rate RMR?
Resting metabolic rate RMR is often confused with BMR.
However, in contrast with BMR, which indicates the minimum calories you need for survival, resting metabolic rate is the total number of calories your body burns when at rest. Understandably, the RMR value or resting energy expenditure is higher than the BMR.
How Does BMR Calculator Help You Lose Weight?
BMR is considered one of the best and safest ways to hack your weight loss journey.
To lose weight and for calorie calculations, BMR is considered a better and more dependable result as it’s the calorie count you absolutely need. The additional amount can be worked out depending on your ideal weight.
It is also important to mention that according to an American journal, basal metabolism is also helpful in predicting weight gain.
How Many Calories Do You Need In A Day?
To fully grasp how you can use BMR to lose fat, let’s first discuss total energy requirements.
Remember that BMR is the minimum amount of calories you need in a resting state. You still need additional energy for walking, talking, running, food digestion, and other daily activities.
Therefore, while BMR estimates calorie, it is crucial to know exact energy needed in a day (calories burned in a day), which in other words, is termed total daily energy expenditure or TEE in clinical nutrition.
The basal metabolic rate is 60% to 80% of TEE.
Your daily energy expenditure or TEE has four components:
- Sleeping metabolic rate or SMR
- Thermic effect of food
- Physical activity
- Energy cost of arousal
Online TEE calculators can help you figure out energy expended or TEE.
Now once you have daily energy expenditure or TEE in hand, you can get to your calorie needs for weight loss.
One of the most popular methods used in clinical nutrition is the 500-calorie deficit, which says your calorie intake should be 500 calories less than TEE. Theoretically, this practice guarantees the loss of 1 lb of fat in a week.
Some experts also recommend reducing your calories by 10% to 20% of TEE.
Nevertheless, it is crucial to talk to a nutritionist, especially when aiming for significant loss of fat.
Once you’ve figured out your caloric needs and restriction, it’s time to divide your macros.
Macros are the three vital nutrients, i.e., protein, carbohydrates, and fat, that are essential to carry out vital body functions.
Ideally, the distribution of the three macronutrients in your diet should be as follows:
- Proteins – 10% to 35%
- Carbs – 45% to 65%
- Fats – 20% to 35%
One gram of protein, carbohydrates, and fats metabolize to give 4, 4, and 9 calories, respectively.
Work your way around these macros, keeping your ideal body in mind, and you would be able to lose weight (in a healthy manner) in no time.
Other than an individual’s BMR, tools like online calorie calculator can also be used to calculate appropriate calorie requirements in diet.
What Is a Basal Metabolic Rate Calculator Tool?
A basal metabolic rate calculator is an online tool that employs Mifflin-St Jeor, Katch McArdle, or Harris-Benedict equations to for calculating BMR.
All you need to do is put in your age, gender, height, and weight, and the calculator will generate a rough estimate of your BMR for different levels of physical activity.
Here are the different formulas used for BMR calculation:
Mifflin St Jeor Equation
Mifflin St Jeor equation is generally considered the most accurate method for close-to-accurate BMR results.
BMR = 10 x weight in kg + 6.25 x height in cm – 5 x age + 5
BMR = 10 x weight in kg + 6.25 x height in cm – 5 x age – 161
Revised Harris Benedict Equation
Harris Benedict equation is the first BMR formula, however, it has been revised for accuracy.
The revised Harris Benedict formula used as a basal metabolic rate formula is as follows:
BMR = 13.397 x weight in kg + 4.799 x height in cm – 5.677 x age + 88.362
BMR = 9.247 x weight in kg + 3.098 x height in cm – 4.33 x age + 447.593
Note that Harris Benedict formula is still less accurate than Mifflin St Jeor equation.
Katch Mc Ardle BMR Formula
BMR = 370 + 21.6 (1 – body fat percentage) x weight in kg
When using the above formula, an online body fat calculator can be used for fat percentage.
Although Mifflin St Jeor equation is overall more accurate, Katch Mc Ardle is considered more reliable to calculate BMR in leaner people, as it takes body fat into account. It is primarily used for resting metabolic rate RMR.