Have you ever thought that even when we are just sitting still, that is, lying in bed or in a chair, our bodies are constantly working? Breathing, our heart beating, and regulating our body temperature are just a few of the many things that we do. So all of this requires energy, which is calories. That minimum amount of energy is what we call our BMR.
What is BMR (Basal Metabolic Rate)?
Simply put, BMR (Basal Metabolic Rate) is the minimum number of calories your body uses to maintain the basic processes necessary for survival when you are not doing any work, just at rest. Imagine, even if you were lying in bed all day, your breathing, blood circulation, cell repair, and maintaining body temperature are still happening, right? That's what this energy is used for. This BMR value varies from person to person. There are many reasons for that, let's talk about that too.
In fact, about 60% to 70% of the total energy we expend in a day goes to this BMR . Another 10% goes to digesting the food we eat and converting it into energy. The rest is spent on things like moving around and exercising.
Many people are interested in knowing about BMR, thinking that it will help them control their weight. This can help you get a rough idea of how much energy your body actually needs per day. But remember, BMR is only one factor when it comes to weight control. There are many other factors that come into play.
What factors affect our BMR?
Okay, now let's look at the factors that can affect the BMR value. Some of these things we can't change, but some things are within our control.
Permanent factors that we cannot change much:
- Body size: The larger your body, meaning the more tissues and cells it has, the more energy it takes to maintain them. Just like a bigger house costs more to maintain.
- Amount of lean muscle tissue: Muscle tissue is like the engines in our bodies. It takes a lot of energy to maintain it. The more muscle you have, the higher your BMR will be.
- Amount of adipose tissue (body fat): It takes less energy to maintain adipose tissue than muscle tissue. However, adipose tissue also requires energy. So, the amount of fat also affects BMR to some extent.
- Sex: Men generally have a slightly higher BMR than women. This is because men are generally larger than women and have more muscle mass due to the hormone testosterone.
- Age: BMR gradually decreases as we age. The main reason is the loss of muscle mass as we age. In addition, hormonal changes and neurological changes can also affect BMR.
- Race: Research has found that your race or ethnicity can also affect your BMR, but more research is needed on this.
- Genetics: Our genes also have a big impact on BMR. Some people are born with a fast metabolism, while others have a slow one. Researchers are still figuring out exactly how these genes work.
Things that temporarily affect BMR:
- Skipping meals, fasting or starvation: Imagine, if you don't eat properly, if the amount of calories your body receives decreases, your body tries to conserve energy. This is something that evolved to help us survive. Then your body lowers your BMR, which means it slows down the rate at which you burn energy.
- Environmental temperature: If you are in a very cold environment (e.g., when you are sweating) or very hot (e.g., when you are sweating), your body has to work harder to maintain a normal body temperature. Your BMR increases during these times.
- Thyroid hormone levels: Thyroid hormone, which is secreted by the thyroid gland, is very important for our metabolism. If thyroid hormone levels increase, which is a condition called hyperthyroidism, BMR increases. Similarly, if thyroid hormone levels decrease, which is a condition called hypothyroidism, BMR decreases.
- Illness or injury: When you have a fever or an injury, your body has to do extra work. That means fighting off illness and repairing tissues. This increases your BMR.
- Stimulants: BMR can temporarily increase when you use stimulants such as caffeine (found in coffee and tea), nicotine (found in tobacco), and amphetamines.
Effects of different stages of life on BMR:
- Growth: Young children, especially babies, are growing rapidly. They need more energy to grow new tissue and gain weight. Therefore, their BMR is higher.
- Pregnancy: During pregnancy, a mother's body mass increases, and the growth of the fetus in the womb requires additional energy. This increases the BMR of a pregnant mother.
- Lactation: Breastfeeding also requires extra energy from the body. Research has shown that producing breast milk requires between 15% and 25% extra energy .
- Menopause: Hormonal changes that occur with menopause can cause a loss of muscle mass. This is usually the cause of a decrease in BMR.
Is there a "normal" BMR value?
There is no such thing as a 'normal' BMR value. Because of the many factors we discussed earlier, each person's BMR is different. Scientists can only give average values. Remember, these are just rough estimates.
The average BMR for a man is about 1,696 calories (7,100 kilojoules) per day . For a woman, it is about 1,410 calories (5,900 kilojoules) per day . However, these values can vary slightly depending on your race/ethnicity.
The important thing is, these calories are only used to perform basic bodily functions. This doesn't include the calories we burn from food, or the calories we burn while walking, working, or exercising!
If you want to know exactly how many calories you need per day, it's best to talk to your doctor or a registered dietitian. They can calculate this for you based on your situation.
How do I calculate my BMR?
To accurately measure BMR, it must be done in a lab setting, following very strict rules. That is:
- You need to be completely relaxed.
- You need to be completely calm, both mentally and physically.
- The measurement is taken after waking up after a good night's sleep, 12 to 14 hours after the last meal.
- You should stay in a room with a comfortable temperature.
Now, not everyone can go to a lab like this and measure their BMR. That's why scientists have developed equations to roughly calculate BMR. One of the most commonly used is the Harris-Benedict equation .
How to calculate BMR using the Harris-Benedict equation:
For men:
`BMR = 88.362 + (13.397 x weight in kilograms) + (4.799 x height in centimeters) - (5.677 x age in years)`
For women:
`BMR = 447.593 + (9.247 x weight in kilograms) + (3.098 x height in centimeters) - (4.330 x age in years)`
It is important to remember that these equations only provide a rough estimate .
Let's also learn about RMR (Resting Metabolic Rate) calculations.
You may have heard the term RMR (Resting Metabolic Rate) . RMR and BMR are similar, but there is a slight difference. RMR is the amount of energy your body uses to function when you are at rest. However, it also includes calories burned for small, low-energy activities like going to the bathroom or getting dressed. That's why RMR is usually about 10% higher than BMR.
There are also equations to calculate RMR (these are usually based on weight in pounds and height in inches):
For men (RMR):
`RMR = (4.38 x weight in pounds) + (14.55 x height in inches) - (5.08 x age in years) + 260`
For women (RMR):
`RMR = (3.35 x weight in pounds) + (15.42 x height in inches) - (2.31 x age in years) + 43`
These are just rough calculations, right?
Can I increase my BMR?
Most of the time, there's little we can do to significantly change our BMR. Because we can't change things like genes, age, or height. But one way to increase our BMR in a healthy way is to increase our lean muscle mass . As we've said before, it takes a significant amount of energy to maintain muscle tissue. So, as muscle increases, BMR also increases.
Exercise, especially resistance training and strength-training exercises – which are different from aerobic exercise – can help build muscle when done regularly. Examples include lifting weights, Pilates, and kettlebell training.
But, remember, intentionally increasing your BMR too much isn't always a good thing. For example, someone with a serious illness like cancer may develop a condition called hypermetabolism, which means their metabolism is too fast. Also, conditions like hyperthyroidism or the use of certain stimulants can increase your metabolism, but they can also be harmful to your health.
If you have questions or concerns about your metabolism, how it affects your weight and health, or if you have any doubts, be sure to talk to your doctor.
So, what are the most important things we should take home from this story?
Knowing your BMR, the minimum amount of energy your body uses at rest, is a good first step in taking control of your weight and health. Of course, we can't change BMR much. But it's only one important part of the bigger picture.
If you'd like to learn more about your body and the factors that affect your weight, don't hesitate to see your doctor or a metabolic specialist. They can create a personalized plan that's tailored to your body and your goals. That way, you can be on your way to a healthier life.
Remember, a healthy lifestyle isn't something that happens overnight. It's a journey. Start small, know what's right, and move forward with patience.
` BMR, Basal Metabolic Rate, Calories, Energy, Metabolism, Weight Management, Health
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