Losing and gaining weight are, in fact, pure mathematics. To lose weight, you need to take in less energy with your meals than what you spend on a daily basis to keep your body healthy, work, do your chores and exercise. If you want to gain weight, you need to supply more calories. While this may sound trivial, anyone who has ever tried to consciously control their body weight by manipulating the calorie content of their diet knows that practice proves otherwise. The first step is always to determine your calorie needs, and for this you need to learn the meaning of the abbreviations: BMR, TMR and PAL. I will explain everything to you step by step.
Grab a calculator and let’s go!
Basal metabolic rate (BMR) – the calories you burn without doing anything
BMR stands for the basal metabolic rate. BMR is expressed in calories and is defined as the energy required by your body to perform basic life-sustaining function, i.e. to sustain the activity of vital organs. More specifically, BMR means that calories you would use resting all day long, without the slightest movement, in a comfortable temperature, after fasting for 12 hours.
Most of the BMR calories are used up by:
- the nervous system and brain – ca. 25% of the energy,
- the liver – ca. 20% of the energy,
- the kidneys and heart: ca. 7% of the energy each.
The other organs account for the remaining 40% of your daily energy consumption. Note how energy-intensive the brain function is!
Two formulas are most often used for BMR calculations: the Mifflin formula or the Harris-Benedict formula. The calculations deliver similar results. In my practice, I usually use the Harris-Benedict formula.
Male BMR formula:
BMR = (13.7516 × W + 5.0033 × H – 6.7550 × A + 66.473)
Female BMR formula:
BMR = (9.5634 × W + 1.8496 × H – 4.6756 × A + 655.0955)
W stands for weight in kilograms
H stands for height in cm
A stands for age in years
You can calculate BMR with a calculator or use one of the online BMR calculators where you only need to input your sex, body weight, height and age.
BMR is the energy you absolutely need to stay alive. If you don’t deliver this amount of calories in food, your body will somehow have to draw that energy from glycogen, fatty tissue, or burning your muscles. It is very important to never set the calorific content of your meals below the BMR value. This upsets the metabolism and will easily push you into a vicious circle of weight loss, yo-yo effect and various metabolic disorders.
Total metabolic rate (TMR) – all the calories you spend in a day
TMR is another important abbreviation that stands for total metabolic rate, or your total daily energy expenditure. TMR includes the calories you burn to move, exercise, walk, work, or even sleep. To calculate TMR, you need to know your PAL.
Finding out your physical activity rate (PAL)
To calculate your calorie needs and determine the daily calorie intake, you need to know one more abbreviation: PAL (this is the last one, I promise). PAL stands for physical activity level and is an estimation of your daily activity and the related daily calorie expenditure. PAL is not specifically calculated but estimated based on certain descriptions by matching your activity level to the definitions that best reflect your lifestyle.
Accurate estimation of the PAL parameter requires some skill and experience, so if you have the opportunity, the easiest thing to do here is to consult a dietician, who will quickly assist you in selecting the right PAL for you. You can also try and choose the physical activity level that suits you best:
- PAL = 1.2 for people with extremely low physical activity, who spend time mostly without moving, bedridden patients and obese people with BMI>30, e.g. elderly people with limited mobility.
- PAL = 1.4 for people with low physical activity, spending most of their day sitting, walking occasionally (about 3 hours a week) or choosing low-intensity sports activities, e.g. students commuting to university by public transport, not exercising.
- PAL = 1.6 for people with moderate physical activity, e.g. people with non-sedentary occupations or sedentary work who devote several hours a week to exercise, e.g. postmen, office workers attending intensive group exercise classes 3 times a week, walking the dog every day.
- PAL = 1.8 for people with strenuous physical activity, who are manual workers or devote 1-2 hours daily on average to high-intensity sports, such as volleyball, football, continuous swimming, intense zumba.
- PAL = 2 for people with extremely strenuous physical activity, whether work-related or not. These are primarily athletes who train intensively every day (or even twice a day), but also miners or foundry workers.
If you are unsure which PAL to choose, you can of course pick a value ‘in between’ the above levels, e.g. PAL = 1.5 or PAL = 1.3. Besides, you need to be aware that unexperienced people tend to overestimate their physical activity levels.
Pay particular attention to what your daily life looks like. If you work with a computer from Monday to Friday, you usually choose reading or watching a TV show as your pastime, but you happen to go out for sports (but not more than three times a week), your PAL will be closer to 1.4 than 1.6. The examples in the last paragraph should help you choose your PAL.
Calculating TMR based on PAL
If you have already calculated your BMR (basal metabolic rate) and determined your PAL, you can easily calculate your TMR (total metabolic rate).
TMR = BMR × PAL
TMR is the exact calorie intake that you should stick to if you want to neither lose weight nor gain weight. This is the energy needed to keep your body weight constant, on the assumption that your daily habits will not change.
Energy needs: how to determine the calorie intake?
If you are calculating BMR and TMR to establish your recommended calorie intake, you are almost there. If you want to shed a few kilos, set your calorie intake below TMR, and if you want to put on weight, it must be higher than your TMR.
Determining the calorie intake in a weight-loss diet
A weight-loss diet should be higher in calories than your BMR (always, no exceptions!) and lower in calories than your TMR. You need to decide how many calories to subtract from TMR, or choose your calorie deficit.
To start with, you should go around 300-400 kcal below your TMR to see how the body reacts to the reduction. Subsequently, you can adjust the deficit to your needs if you find that it’s not working after a few weeks.
Determining the calorie intake in a bulking diet
To gain weight and muscle mass, you need to eat more than you burn. This is a bit of oversimplification, less-trained people can also build muscle while losing fat, but that’s a different story. To put on weight, you need to set your calorie intake above your TMR. Add 300-400 kcal or more to your calculated TMR if you want to gain fast.
Calculating the BMR, TMR and calorie needs: practical examples
Even if you read the article very thoroughly, this will not help you understand the calculation of calorie needs as much as practical application of these insights. For example:
Ewa, 29, is 168 cm tall, weighs 73 kg and is trying to shed a few kilos. Her work is sedentary, from Monday to Friday she spends most of her time in the office, commuting by car. For some time, she has been taking part in various sports activities 3 times a week, using her MultiSport card. She most often chooses aerobics, Pilates, salsa or yoga classes. She usually spends her weekends in the city, mainly exploring new eateries with her friends, in the summer she sometimes goes on a cycling trip or inline skating.
BMR (using the formula) = 1,528 kcal
PAL = 1.4
TMR = 2,139 kcal
Selected calorie deficit = ~400 kcal
Calorie intake in a weight-loss diet for Ewa = ~1,700 kcal
Peter, 43, is 184 cm tall, weighs 75 kg and is trying to put on weight. He works as a postman in a small town, gets around by bicycle at work, and has recently been going to the gym twice a week and doing classic strength workout there, which has been set up by a personal trainer.
BMR = 1,726 kcal
PAL = 1.6
TMR = 2,761 kcal
Calorie intake in a bulking diet for Peter = ~3,200 kcal