Calculate Basal and Resting Metabolic Rate

abs mWhen we calculate our Basal Metabolic Rate (BMR) or very similar Resting Metabolic Rate (RMR), we calculate the amount of energy expended while at rest, per day. It must be noted that this is calculated for resting in neutrally temperate environment while digestive system is inactive (at least 12 hours after eating food).

Energy released in this state is enough for functioning of vital organs (brain and nervous system, hart, lungs, liver, kidneys, liver, sex organs, muscles, intestine, skin).

RMR is the calories body burns while at rest. If you got up in the morning and went from your bed to the couch and watched TV the entire day (or even better, you watched TV from your bed), this would be a pretty good estimate of your daily calories.

Daily calories depend on BMR, working habits and environment. So every result for BMR must be corrected (multiplied) with some factor (generally 1.2 - 2.0) to obtain daily needed calories for maintenance only. If we want to lose fat, we will subtract for example 500 kcal and if we want to bulk up (build muscles), we will add for example 500 kcal per day. Since, people are all different, these numbers are just general guidelines and some corrections from time to time are needed - you should check your weight once a week and accordingly eat more or less.

There are many methods and formulas for calculating BMR, some of them are presented here.

Harris-Benedict Equation (BMR)

Harris-Benedict equation is method used to estimate BMR of individual based on gender, weight, height and age.

BMR (men) = 66 + (13.7 x weight in kg) + (5 x height in cm) - (6.8 x age)
BMR (women) = 655 + (9.6 x weight in kg) + (1.7 x height in cm) - (4.7 x age)

These formulas don't take into account difference in metabolic activity between metabolically active cells (muscle cells for example) and fat cells (which don't need much calories for maintenance). Formulas that take into the account lean body mass (LBM) is the Cunningham formula (which is used to predict RMR, not BMR) and the Katch-McArdle Formula (BMR).

The Katch-McArdle Formula (BMR):

The Katch-McArdle Formula calculate BMR based on LBM (Lean Body Mass):

BMR = 370 + (21.6 x LBM)

Since LBM is mass of body without body fat, this formula is more accurate for athletes who have above average lean mass and not much of body fat.

The Cunningham Formula (RMR)

The Cunningham Formula calculate RMR based on the LBM (Lean Body Mass).

RMR = 500 + (22 x LBM)

Just as the Katch-McArdle formula, the Cunningham formula uses LBM and not the full body mass - this formula is more accurate for athletes who have above average lean mass and less body fat.

 IMHO, fastest way to approximately calculate your BMR is to simply multiply your weight in pounds with 10 or your weight in kilograms with 22. This method many consider also as the least accurate method, which I doubt (check table with examples of calculated BMR and RMR).

After calculating BMR (RMR), in order to get real energy expenditure, we multiply obtained BMR (RMR) with factor that depends on physical activity:

Physical Activity Level Factor

1.2

1.4

1.6

1.8

2.0

Physical Activity Level

Very Light Activity

Light Activity

Moderate Activity

High Activity

Very High Activity

Very light activity would be doing nothing physical (just desk job) and no physical activity all day long.

Light activity would be having desk job and some sort of physical activity like walking for few kilometers, but no workout.

Moderate activity would be desk job in combination with some sort of activity during the day and workout session in the gym (or cardio on track) - this is where most of trainees are.

High activity would be combination of non-physical job and two daily workout sessions or physical job and workout session.

Very high activity would be hard physical job and workout session.

Example:

We have two persons:

- woman, 30 years, 170 cm, 70 kg, 15% bf

- man, 30 years, 185 cm, 100 kg, 10% bf

Their results are given in following table:

Person The Harris-Benedict Equation (BMR) The Cunningham Formula (RMR) The Katch-McArdle Formula (BMR) Multiply by 22 (10) Method
Woman 1475 kcal 1809 kcal 1655 kcal 1540 kcal
Man 2157 kcal 2480 kcal 2314 kcal 2200 kcal

As one can see, 'scientific formulas' are comparable with simple 'Multiply by 22 (10) Method' :o)

BMR for woman in example would be around 1550 kcal and for a man BMR would be around 2200 kcal. If we multiply with Physical Activity Level Factor of 1.6 (Moderate Activity), we obtain necessary calories for both persons needed to keep current weight at present physical activity: woman - 2480 kcal, man - 3520 kcal.

Now, after crunching numbers, we know how many calories woman and man from example need to consume to lose mass, stay at current level or even gain more mass.

Of course, these numbers are just approximation of real life, but IMHO very good starting point.