If you think that you have some excessive body fat and are going to lose weight, you should find out how many calories1 you burn during a day. It will help you to understand what number of calories you can eat per day. Then you will have to adjust the calorie count and start losing weight and burning fat.
According to the USDA:
An average man consumes about 2500 calories in a day
An average woman consumes 2000 calories in a day
If they do not put on weight, it means that they burn these calories during a day.
But the numbers are too approximate, and if you want to know more exactly how many calories you burn in a day, you have to take into account three main aspects: basal metabolic rate2, physical activity level, and digesting food.
Let’s talk about them in detail.
Basal Metabolic Rate
Your body is working without rest. Your heart is constantly pumping blood, your hair and nails are growing, your lungs are supplying you with fresh air. The body has to repair small damages and keep normal temperature. This work requires a lot of energy. In fact, more than 60% of all the calories burned in a day are burned by keeping your body working.
The minimum number of calories required for completing the basic functions of the body is known as the basal metabolic rate. And the BMR lets you know how many calories should be eaten in a day if you don’t want to damage your health.
The basic metabolic rate depends on your weight, height, age and gender. Some factors (like walking in a park, general swimming or moderate effort bicycling) can increase the BMR, while others (age, fasting or starvation) decrease it. Men have the higher BMR than women.
Factors, Affecting the Basic Metabolic Rate
Very hot or very cold weather
Estimating the BMR is a rather complicated process, but there is a simple method giving rough results. Here is the formula:
BMR = a body weight (in lb) x 10
E.g. 200 pounds x 10 = 1860 calories.
If you need more exact calculations, you may use Harris-Benedict equation or online BMR calculators.
Finding out your BMR is the first step to calculating the daily caloric expenditure. The second step is estimating how many calories you use in physical activity.
Physical Activity Level
Any physical activity causes calorie expenditure. Simple walking, vigorous effort bicycling, pound load climbing will help you to lose weight. The percentage of calories burned by physical activity can be from 20% to 50% of all the calories you spend in a day. It depends on you activity level. Look at the table below.
You are sitting almost all the day
You are walking, doing daily chores
You are walking much, doing exercises
You are a sportsman
You know your BMR and can calculate the number of calories burned due to your physical activity by using the appropriate percentage from the table. For example, you weigh 200 pounds, your BMR is 1860 calories, and you are lightly active. So, 1860 x 35% = 651 calories.
Now you are almost ready to calculate the daily caloric expenditure, but you need to take into consideration one more factor. It is the energy which is burned while digesting food. Are you surprised? Digesting food does require energy.
What is more, for digesting some kinds of food, like protein, your body needs more energy than for digesting others. But don’t think that you can eat nothing but protein, because you must get a balanced diet.
Digesting food burns about 10% of the daily caloric expenditure
For the lightly active man who weighs 200 pounds and has BMR equal to 1860 calories, the number of calories burned from digesting food will be following: (1860 + 651) x 10% = 251 calories.
Daily Caloric Expenditure
Now you can easily calculate the total daily caloric expenditure by adding numbers of calories burned by BMR, physical activity and digesting foods.
E.g. 1860+651+251=2762 calories.
This is the calorie expenditure for the man we talked about above. If he wants to lose weight without changing his life-style, he has to eat less than 2760 calories in a day.
Remember that one pound of body fat equals to about 3500 calories. If you are going to lose one pound per week, you must cut off 500 calories per day. It means that you have to eat less or do more exercises.
The calorie is a widely-spread unit of heat energy, which is commonly used for measuring the food energy value. It was defined in 1824 by scientist Nicolas Clement.
The basal metabolic rate (BMR) is an amount of energy that a human being or an animal uses in dormant state. This amount of energy is sufficient for the vital organs (heart, kidneys, lungs, skin, etc) to function properly.