5.14 Basal Metabolic Rate
Alright, the next term we need to know is the basal metabolic rate. The basal metabolic rate or BMR is the number of calories that your body uses each day to do normal bodily functions, even if you did nothing but laid in bed all day. The metabolism of the body is quite complicated as behind the scenes there are a lot of things going on everyday in your muscles and organs. A person’s basal metabolic rate will be different based on a number of factors including:
- Weight (including muscle mass)
- Athletic ability
- Calorie intake (avoid crash diets which lower your BMR)
Now, the most accurate way to know your exact basal metabolic rate is to do a specific test called a “resting metabolic test” during which your heart rate, oxygen use and CO2 elimination are measured. This requires some specific equipment and is not something you can do at home. To be very accurate, you can find a local fitness center that offers this test, but it may cost you near $100.
We can get a free estimate of your basal metabolic rate with a simple calculation.
For men: BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years) + 5
For women: BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years) – 161
Lets do some quick examples. Here are 3 men.
Note that the older you are, the lower your basal metabolic rate by about 5 calories per year. So when you hear people say that it is more difficult to lose weight as you get older, this is one of the reasons why.
Another interesting fact to know is that for every pound of muscle mass that you build, your basal metabolic rate increases by 50 calories per day! This is why resistance training (weight lifting) can be quite helpful in your exercise routine. If you build a little muscle mass through weight lifting, you will burn off more calories every day. This fact is not included in the generic basal metabolic rate equation, but will be counted during a resting metabolic test if you pay for one.
OK…Lets put some of this information that we have learned together to figure out how many calories you use in a day, which is based on this simple equation:
Calories burned each day = Basal metabolic rate + calories used during normal daily activity + calories burned during exercise
The calories you use during normal activity simply depends on what you do throughout the day. If you have a desk job and sit most of the day you will burn much fewer calories than if you have a physical job. We do have ways to estimate this number including the increasingly popular gadgets like the Apple Watch and the Fitbit. Most people burn about 200 to 400 calories per day with activity, but again that depends on your specific activity level.