Calculating your caloric needs

Having learned the basic theoretical aspects of performance-oriented nutrition, we are now in a position to put what we have learned into practice. And what better way to do this than to start planning our own meal plans step by step.

In this presentation we will learn how to calculate our energy needs, because as we have already explained they are the first element we must take into account when planning our diet. Let's remember that if there is not an adequate correspondence between the amount of calories we spend daily and the calories provided by the diet, the meal plan will lead us to obesity or malnutrition.

How many calories does your body expend to maintain all vital functions?

The first thing to know is approximately how many calories your body uses to maintain the vital functions of the organism (blood circulation, heartbeat, temperature, liver function, nervous system, kidney function, etc.). This amount of energy your body uses to keep you alive is called the basal metabolic rate.

We might think that we expend few calories when we are at rest, but this is not the case; the basal metabolic rate represents between 60% and 75% of the total energy expenditure. Only those people who perform very intense physical activities use more calories than they need to keep all their organs and systems functioning.

Do all people have the same basal metabolic rate?

Of course not, organisms with a greater amount of metabolically active body tissues expend more calories to maintain all their vital functions. To better understand this, let's look at the following example:

• Between two people of the male sex, of the same age, with equal body weight, the one with more muscle tissue will have a higher basal metabolic rate, since muscle tissue is more active than adipose tissue.

• Therefore, in general, men have a higher basal metabolic rate than women, young people more than the elderly, muscular people more than obese people, and so on.

But there are other factors that also influence the basal metabolic rate, for example:

• The stages of the life cycle (stages of growth, pregnancy, etc.).

• Body temperature (high ambient temperature, body fever, etc.).

• Stress, consumption of stimulating substances (coffee, tea, etc.).

How is the basal metabolic rate calculated?

The formulas for calculating the basal metabolic rate obviously offer only an approximate figure, because the exact value, as we have just explained, depends on many factors.

One of the most accurate formulas is the Katch-McArdle formula because it takes into account muscle mass and lean mass, but the measurement of these parameters is also inconvenient for many.

This is why we will show you how to calculate your basal metabolic rate using the Harris-Benedict formula, which is undoubtedly the most commonly used, although it can give a considerable margin of error when the individual has a high rate of muscle or fat mass.

Basal metabolic rate using the Harris-Benedict formulas (BMR) from weight (W) (kg), height (T) (cm) and age (years):

• For women -» BMR = 655 + [9.6 x P (kg)] + [1.8 x T (cm)] - [4.7 x age (years)].

• For men -» BMR = 66 + [13.7 x P (kg)] + [5 x T (cm)] - [6.8 x age (years)].

Example: Let us calculate the basal metabolic rate of a woman weighing 65 kilograms, 170 centimeters tall and 40 years old.

We will substitute the values in the formula for women and calculate:

• BMR = 655 + (9.6 x 65 kg) + (1.8 x 170 cm) - (4.7 x 40 years old).

• TMB = 655 + 624 + 306 - 188

• TMB = 1585 - 188

• TMB = 1397 kcal.

Calculation of daily energy requirements

We already know the amount of calories our body spends when we are resting, lying down, doing nothing else; but we need to know the amount of calories we spend throughout the day, since even the most sedentary people need calories to walk, read, watch TV, work on the computer, and so on.

The total daily energy requirements are calculated by multiplying the value we obtained from the basal metabolic rate by an index that represents the level of physical activity we perform daily. Of course, the index is higher when a greater number of physical activities are performed throughout the day.

The formula is as follows:

• Daily caloric needs = BMR x physical activity index.

There are different tables to obtain the physical activity index. Below we will show those proposed by Harris Benedict:

• Example of the calculation of daily caloric needs.

• Daily caloric needs = BMR x physical activity index.

For the value of the basal metabolic rate (BMR) we will use the result we obtained in the previous example, which was 1397 kcal.

We will consider that the level of physical activity is moderate (between 3-5 days a week), so we look in the table for the index that corresponds to it (1.55). Then we substitute and calculate:

• Daily caloric needs = 1397 kcal x 1.55.

• Daily caloric requirements = 2165 kcal