How to Estimate Calories for Weight Loss

Weight loss in theory is a simple matter. It occurs when the number of calories burned by the body are greater than the number of calories consumed through eating. The number of calories the body uses on a daily basis is known as the Total Daily Energy Expenditure (TDEE). TDEE is also known as the "maintenance level". If a person consumes fewer calories than their maintenance level, then they should lose weight. On the other hand, if a person consumes more calories than their maintenance level, they will gain weight.

About 70% of TDEE is comprised of the Basal Metabolic Rate (BMR). The Basic Metabolic Rate is the number of calories that the body needs to sustain its essential functions and processes. A person's BMR depends on a variety of factors. Some of the factors, which affect BMR are;

1)Weight-Higher weight means a higher BMR. This fact contradicts the idea that people with weight problems suffer from a low metabolism. In fact, over weight people often have a higher metabolism than thin people.

2)Height-Obviously, a person's weight alone cannot be used to determine whether that person is overweight or obese. A person weighing 215 lbs is not likely overweight when they are 6'3". However, a person who is 5'4" and weighs 215 lbs is likely overweight or even obese.

3)Gender-Men, in general, have higher percentages of lean body mass than women. Lean body mass burns more calories than does fat. Accordingly, men will usually burn more calories throughout the day than will women.

4)Age-Unfortunately, people's metabolism tends to slow down when they age, meaning that their bodies will burn less calories throughout the day.

Their are really two ways for people to measure their BMR. One is by direct measurement. Direct measurement is the most accurate method. The direct measurement method is kind of a complicated process. It is usually done through indirect calorimetry. Indirect calorimetry is method of determining energy expenditure through the analysis of gas. Because it is somewhat complicated, direct measurement of BMR is not used most of the time. The more common method of determining BMR is to calculate it by the use of a formula. Several different formulas have been established to determine BMR. Each formula has its strengths and weaknesses for predicting BMR.

One of the most commonly used and oldest BMR formulas is the Harris Benedict Formula. The Harris Benedict Formula is given by the following mathematical expressions:

Metric System of Measurement

Women: BMR=655+(9.6 x weight in kilos)+(1.8 x height in cm)-(4.7 x age in years)

Men: BMR=66+(13.7 x weight in kilos)+(5 x height in cm)-(6.8 x age in years)

English System of Measurement

Women:BMR =655+(4.35 x weight in pounds)+(4.7 x height in inches)-(4.7 x age in years)

Men: BMR=66 + (6.23 x weight in pounds) + (12.7 x height in inches)-(6.8 x age in years)

The Harris Benedict Formula does a pretty good job in predicting BMR. However, it does have a couple of weaknesses that should be understood. For the very muscular, the Harris Benedict Formula will underestimate calories. For the very fat, the formula will over estimate calories. The main reason for the Harris Benedict Formula's weaknesses is that it does not directly take percentage of lean body mass into account. As noted previously, lean body mass burns many more calories than fat. The Harris Benedict Formula implicitly assumes a normal range of lean body mass. Accordingly, people with higher and lower than normal lean body mass will not get accurate predictions. BMR formulas have been developed that directly take lean body mass into account.

Once BMR is determined, TDEE can be computed. Usually, TDEE is computed by multiplying BMR by an "activity factor". An activity factor is dependent upon a person's level of activity. Determining the appropriate activity factor is a matter of judgement. There are no hard and fast rules. Activity factors are shown by the following:

Sedentary 1.2 (little to no daily exercise. Job not physically demanding.)

Lightly Active 1.375 (light exercise 1 to 3 days per week)

Moderately Active 1.55 (moderate exercise 3 to 5 days per week)

Very Active 1.725 (rigorous exercise 6 to 7 days per week)

Extremely Active 1.9 (daily rigorous exercise and physical job)

As an example of the foregoing, consider a 6'4 (76 inches) man, 33 years old, and weighing 220 lbs. Also, assume that the man gets a moderate amount of exercise every week. Putting the relevant information into the Harris Benedict Formula gives:

BMR=66 + (6.23 x 220) + (12.7 x 76)-(6.8 x 33)

BMR=66+1386+965.2-224.4=2192.8

Now TDEE has to be determined. Remember that TDEE is found by multiplying BMR by the appropriate activity level. Because it is assumed that the man in our example gets a moderate amount of exercise, his activity level would be 1.55. Accordingly, TDEE is given by the following:

2192.8 x 1.55=3398.8 (rounded to the nearest decimal)

Accordingly, the man in our example will burn approximately 3398.8 calories per day. In order for him to lose weight, he must consume less than 3398.8 calories each day, until he reaches his desired weight. On other hand, he will gain weight if he consumes more than 3398.8 calories per day.

Readers should keep in mind that the foregoing is a very simplified discussion of BMR and TDEE. Their is much more to both of them. However, for many people, the above should permit a reasonable estimation of both BMR and TDEE.