Energy Requirements

Energy requirements should be stated as MJ (mega Joule); in reality, kcal (kilo-calories) are used more commonly. 1 MJ = 239 kcal, and 1 kcal = 4.184 kJ.

A variety of models are available for the calculation of individual energy requirements.

Here is a simple formula: 1 kcal/kg BW/h is required to maintain basic metabolism (BMR). Light physical activity increases this amount by -V3 and moderate physical activity by ~2A Intense physical activity doubles it. Here is an example: A 70 kg man would have a BMR of 1 kcal x 24 h x 70 kg = 1680 kcal/d. Add 1/3 for light physical activity, for example, no exercise, sedentary occupation. The resulting daily requirement is 2230 kcal. This simple formula disregards differences based on gender, age, or other individual factors.

Using empirical data, the WHO established tables (A) that are commonly used to predict BMR. This calculated BMR is then multiplied by a factor called Physical Activity Level (PAL). To obtain a precise result, the PAL should be used in combination with the duration of the respective activity, e. g. seven hours of sleep at PAL 0.95, three hours housework at PAL 2.4, etc.

The recent introduction of the method using labeled water permits long-term BMR measurements, allowing the establishment of PAL values for defined categories of activity (B). The BMR of various occupational groups was determined, also taking into account various types of leisure activity. The resulting several-day average is more "user-

friendly" than the calculation of individual activities.

Simplification of the BMR calculations according to WHO and their combination with PAL values yield a practical table (C).

Let's use our example: According to the table, our middle-aged 70 kg man's BMR is 1740 kcal. Combined with a PAL of 1.4, his daily energy requirement would be 2400 kcal/d. According to WHO, the same man would have a BMR of 0.048 x 70 x 3.653 = 7.013 MJ or 1676 kcal/day (see Fig. A). Combined with a PAL of 1.4, his daily energy requirement would be 2346 kcal/d.

The simplest method results in a BMR of 1680 kcal/d (add 1/3 for light physical activity) and a total energy requirement of 2240 kcal/d.

The difference between the table, the exact calculation, and the simple method is no more than 160 kcal/d. Due to the large inter-individual differences in energy requirements, this difference is usually irrelevant for practical purposes.

All of these calculations of energy requirements share one property, though: they only apply to healthy individuals of normal weight, and even then, they represent only a guideline. What counts, in the end, is whether the respective caloric intake achieves long-term stable weight.

I- A. Estimating the BMR (according to WHO 1985)

Age group

Formula for BMR estimate

Women

10 - 18 y

BMR = 0.056 x kgBW + 2.898

19 - 30 y

BMR = 0.062 x kgBW + 2.036

31 - 60 y

BMR = 0.034 x kgBW + 3.538

> 60 y

BMR = 0.038 x kgBW + 2.755

Men

10 - 18 y

BMR = 0.074 x kgBW + 2.754

19 - 30 y

BMR = 0.063 x kgBW + 2.896

31 - 60 y

BMR = 0.048 x kgBW + 3.653

> 60 y

BMR = 0.049 x kgBW + 2.459

Calculation result represents BMR in

MJ/d; multiply by 239 to obtain BMR in kcal/d

Life style and level of activity

PAL

Examples

Chair-bound or bed-ridden

1.2

Elderly, frail

Seated work with no option of moving around and little or no strenuous leisure activity

1.4 - 1.5

Office workers, precision mechanics

Seated work with discretion and requirement to move around but little or no strenuous leisure activity

1.6 - 1.7

Lab technicians, drivers, college students, assembly line workers

Standing work (e.g., housework, shop assistant)

1.8 - 1.9

Housewives, sales persons, waiters, mechanics, craftsmen

Strenuous work or highly active leisure

2.0 - 2.4

Construction workers, farmers, miners, performance athletes

r C. Guideline Table

Teens and adults

MJ/d kcal/d

MJ kcal

15 to < 19 y 19 to < 25 y 25 to < 51 y 51 to<65 y > 65 y

6.1 1460

4.9 1170

  1. 5 2000 8.1 1900
  2. 8 1900 7.4 1800

6.9 1800

9.8 2300 9.3 2200 9.0 2100 8.5 2000 7.5 1800

11,0 2600 10.4 2500 10.1 2400 9.5 2300 8.8 2100

12.2 2900 11.6 2800 11.2 2700 10.6 2500 9.8 2300

Male

15 to < 19 y 19 to < 25 y 25 to < 51 y 51 to < 65 y > 65 y

7.6 1820 7.6 1820 7.3 1740 6.6 1580 5.9 1410

10.6 2500 10.6 2500 10.2 2400

9.2 2200

8.3 2000

12.2 2900 12.2 2900 11.7 2800 10.6 2500 9.4 2300

13.7 3300 13.7 3300 13.1 3100 11.9 2800 10.6 2500

15.2 3600 15.2 3600 14.6 3500 13.2 3200 1 1.8 2800

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