BMR, TDEE and metabolism. These terms can be overwhelming for anyone who wants to start the weight loss journey or may be gain muscles. We will approach metabolism in the most simplest way possible and figure out how many calories we exactly need to reach our goals.
Basal Metabolic Rate (BMR) and factors that influence it
Before we jump to BMR lets understand the basics.
What are calories?
A calorie is the amount of energy needed to raise the temperature of water by 1 degree. When you eat food, it is broken down in the body to produce heat energy. It is this heat energy that fuels your body in the same way gasoline fuels a car.
Calories in food are measured in kilocalories (1000 calories). They are commonly referred to as Calories (calories with capital C).
Simply put, 1 Calorie from food = 1000 calories.
What is metabolism?
We eat food and drink beverages to fuel our body. But, the energy from it doesn’t become readily available to the cells. Our body needs to convert the food into energy that can easily be used by the cells.
This is achieved through metabolism.
Metabolism is a series of complex biochemical process. It occurs in every living organism (including humans).
In simple words, its a process of breaking down what you eat and drink into energy. Calories in food and beverages are combined with oxygen to release energy. This energy is utilized by various parts of your body. At a cellular level, this energy is called ATP.
Digestion of food is the beginning of this process. It ends with the excretion of waste produced during a complete cycle of metabolism.
It’s the metabolism that keeps us alive. Our body is able to grow, reproduce, repair itself by metabolizing the food that we eat.
The number of calories that our body needs to metabolize varies from person to person.
How many calories do you need to eat?
The number of calories that our body needs vary based on the below factors:
- Gender – In general, men need more energy than women to support their current weight. This can be due to the fact women store more fat than men. Also, men carry more muscles than women. But, there is no conclusive study to support this.
- Age – Energy demands decrease as we age. Teenagers have high energy demands when compared to individuals in their 30s or 40s. Body energy demands are very high during growth years and peak at teens.
- Weight – Individuals who weigh more, need more energy to support their weight. Body’s energy requirement is directly proportional to weight.
- Lean Body Mass – Muscles are energy hungry. The more muscle you have, greater will be body’s energy demand.
- Activity Level – Body’s energy demand increase with more active the individual is. People who do the 9-5 job will have significantly less energy demand when compared to a construction worker.
- Weather/Climate – Even the weather can affect the number of calories you need. If you stay in a country where it is mostly cold, you would need more calories to maintain your normal body temperature.
Basically, no two people will have same caloric need even if there were twins.:)
Now that you understand that you can’t just guess your calories, let’s see how we go about calculating it.
Before we jump to the calculations, we need to dig a little deeper.
What is Basal Metabolic rate (BMR)?
Our body is a power hungry machine. Yes, you heard it right. We are nothing but a complex biological machine.
Our body needs fuel to do simplest of the tasks like maintaining body temperature. Every time you breathe, you burn calories. Your heart consumes calories every second, to circulate blood in your body. Organs in your body need the energy to perform various functions.
The calories that are needed for your body to perform these tasks, make up your basal metabolic rate, or BMR.
BMR measures the energy needed by your body to support tasks that keep you alive for a period of 24 hours. Change in your day to day activities cannot raise or lower your BMR.
Think of it as the number of calories that you need just to stay alive while doing nothing (sleeping or resting).
Couple of things to consider here though:
- Women have less BMR than men. This is mainly attributed to muscle mass. Men, in general, carry more muscles than women. Muscles are energy-hungry. This means you can get away with eating more when you carry more muscle mass. 🙂
- In my teens, I could get away with eating chips, donuts, and pastries. If I try that now, I will easily add an inch or two to my waistline overnight. This is because, during our teenage, we had the highest metabolic rate. BMR tends to decline over time as we age.
How to calculate BMR?
Harris-Benedict Principle is the most common way to calculate your resting energy demand (BMR).
However, there have been multiple revisions of the formula.
The Harris-Benedict equations revised by Mifflin and St Jeor in 1990 is the most accurate formula
Men BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
Women BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
So, if you are a 35-year-old man with a height of 180cm, weighing 80kg
Your BMR = (10 × 80) + (6.25 × 180) – (5 × 35) + 5= 1755 Calories
Whereas, if you are a 35-year-old woman with same height and weight
Your BMR = (10 × 80) + (6.25 × 180) – (5 × 35) – 161 = 1589 Calories
You can clearly see that women have less BMR than men. This is one of the reasons why women are more likely to gain fat compared to men when consuming the same amount of food.
What is Resting Metabolic Rate(RMR)?
The body’s demand for calories goes beyond just sustaining life functions. Your body consumes calories even for digesting the food that you eat.
You also burn calories when performing mundane tasks like moving from one place to another or lifting a fork to eat food.
Your Resting Metabolic Rate (RMR) takes into basic body movement as well as digestion of food.
RMR = BMR + Calories consumed during digestion of food & basic body movements
How to calculate RMR?
I don’t recommend calculating RMR as the amount of energy consumed during digestion depends on what you eat in the first place.
Food is mainly (Macros) categorized into Fats, Proteins, and Carbs. Protein consumes the maximum amount of calories to digest, while carbs need the least.
Also, our day to day activities may vary. I am sure during the weekend you love to chill out with friends and family. 🙂
Difference between BMR & RMR and which one is more accurate?
The calculators available online, only provide an estimate of your calorie consumption. Both BMR and RMR can only be measured accurately in a lab setting.
They are measured using gas analysis in a lab.
BMR measurements are taken after 8 hours of sleep and 12 hours of fasting to ensure there is no digestive activity. The lab needs to be a darkened room and the measurement is taken in a reclined position to allow maximum relaxation.
RMR measurements are not so restrictive and can be taken at any time of the day.
Your RMR would always be higher than your BMR. Though, the difference will be small (less than 10%).
Most doctors and health practitioners regard BMR as more accurate than RMR due to the controlled nature of the test.
However, neither of them tell you how many calories you need to eat less to lose fat or more to gain muscle.
That’s where TDEE or Total Daily Energy Expenditure comes into the picture.
What is Total Daily Energy Expenditure (TDEE)?
If you are serious about losing weight or gaining muscle, you need to know exactly how many calories you burn every day.
Total Daily Energy Expenditure is an estimate of total energy that you burn daily. It takes into account energy needed by your body to sustain life (BMR), energy burned through digestion and all your day to day activities. It even includes the calories burned by you while playing with your dog or working out at the gym.
Let’s break it down further:
Apart from burning calories at rest (BMR), your body consumes energy in the following ways
Thermic Effect of Food (TEF)
When you eat food, your body uses a part of the energy from the food to digest the food. It also needs energy for other metabolic processes that are induced by the food.
Every time we eat something our body temperature goes up too. This heat is produced by the brown fat (adipose tissue). The sum of the calories burned during this process is called Thermic Effect of Food (TEF).
Non-Exercise Activity Thermogenesis (NEAT)
From the time you get up till the time you go back to sleep, you perform a lot of activities. Probably you cook food, help your children get ready for school or go to work.
All these activities burn calories. This is called Non-Excercise Activity Thermogenesis (NEAT).
Your NEAT depends on what kind of work you are involved in. A door to door salesman will have a higher NEAT compared to a person with a 9-5 job.
When you hear people saying that move more to lose weight, they are actually referring to NEAT.
To lose weight, you need to burn more calories than you consume. An easy way to burn more calories is to become active.
Thermic Effect of Activity (TEA)
If you are involved in some form of sport or workout regularly, then you burn more calories than the majority of the crowd. The energy consumed while performing a sport or during a strength training or cardio workout is called Thermic Effect of Activity (TEA)
You can burn up to 500 additional calories by picking up a sport or working out consistently.
In essence, the total amount of energy that you need to execute all voluntary and involuntary actions is your TDEE.
Once you know your BMR, you can use the below multipliers based on your activity level to get your daily TDEE
- Sedentary – Spend most of the day sitting (e.g. bank teller, desk job): 1.0 – 1.3
- Low-Active – Spend a good part of the day on your feet (e.g. teacher, salesman)): 1.4 – 1.5
- Active – Spend a good part of the day doing some physical activity or working out 3 days/week): 1.6 – 1.8
- Very Active -Spend most of the day doing heavy physical activity or working out 5 TO 6 days/WEEK): 1.9 – 2.5
If you are unsure about your activity level, stick to 1.3 multiplier. It’s a safe place to start.
Continuing, with the example of the man and woman above.
Female TDEE = Your BMR x 1.4 = 1583 x 1.3 =2058 calories
Male TDEE= Your BMR x 1.4 = 1637 x 1.3 =2128 calories
The Calorie Chart from USDA provides a very good estimate of your daily energy requirement.
Bottom line – BMR doesn’t tell you how many calories you should to eating. It’s your total caloric need that matters. TDEE is the number of calories you need to maintain your current body weight. In fact, its the number of calories that you have been eating on an average.
Hey, isn’t there an easy way to calculate all this in one go?
Sure there is :). Follow the link below.
If you want an easy way to know your total energy expenditure you can use a weighing scale machine that provides TDEE along with your weight. Below are a couple that I recommend.
How to play with TDEE to lose weight
- Caloric Deficit: Once you know the total number of calories you actually need (TDEE), you can carve out a meal plan accordingly. The goal should be to eat about 200-300 calories less than what you are currently eating. You should aim not to go below your BMR as that can slow down your metabolism in the long run.
- Increase NEAT – Instead of sitting all day and watching Netflix, you should try to get involved in something more productive. Maybe pick up a hobby or fun activity.
- Increase TEA – Though the amount of food you eat is the most important factor for losing or gaining weight, physically strenuous activities does have a significant role to play as well. You should aim to workout at least 3 times a week. A strength training routine of 20 mins followed by 10 mins cardio would be a perfect way to burn away the fat sitting on your belly.
You should try to cut down on your calories slowly. Do not cut down your calories more than 10-15% of your current TDEE. Drastically, cutting down on calories can have a rebounding effect. Your metabolism might slow down and once you start eating normally, you will end up gaining more fat. You can learn from biggest losers and don’t repeat their mistakes.