All formulas for determining our daily calorie requirement are only an approximation, albeit a very good one. They can be used very well since the daily calorie consumption can be calculated for both the basal metabolic rate and the total metabolic rate.
The calculated values give primarily a good quantitative reference point about our nourishing way. So how many calories we consume per day.
Formulas for calculating the calorie requirement
Secondarily, we learn about how low or how high our calorie requirement for our activity of daily life (ADL) is. The following 2 formulas can be used for this purpose, which I will discuss later in this article:
- PAL (= Physical Activity Level)
- MET (= Metabolic Equivalent of Task)
However, the most important thing – with all formulas and numbers – is to regard them merely as help and means to an end. We must not lose common sense and rely blindly on these formulas. Because numbers and formulas are without soul and feelings. But humans may – and must – also from time to time hit over the strands may.
Definition and calculation of the Basic Metabolic Rate (BMR)
Basic metabolic rate is the amount of calories required by the body per day (= 24 hours) at complete rest, at indifferent room temperature (28 °C) and sober to maintain its function. The basal metabolic rate depends on factors such as gender, age, weight, height, muscle mass, thermal insulation through clothing and the state of health (fever).
Example Basal Metabolic Rate:
A woman / a man, weight 70 kg, height 170 cm, age 30 years, have approximately the following basal metabolic rate in watts.
Mann: 6997 kJ/24 h (1671 kcal/24 h) = 6997 kJ/86400 sec = 0.080 kW = 80 W Woman: 6248 kJ/24 h (1492 kcal/24 h) = 6248 kJ/86400 sec = 0.072 kW = 72 W
70-80 % of the energy is given off as heat. The heating output of a human being corresponds approximately to the output of a 60 W light bulb or a candle. Per day the body loses 1-2 liters of water by sweating, this corresponds to a cooling capacity of about 30 W. The consumption (in watts) increases with increased physical activity. This is referred to as power consumption. More on this later.
Measurement of basal metabolic rate
Already in the 18th century, the basal metabolic rate was measured by the so-called calorimetry. In humans, so-called indirect calorimetry was used. This indirectly calculates the released energy via the measured oxygen consumption of an organism. For everyday life outside scientific research, however, this is too costly and outdated. Nowadays, in spirometers within a spiroergometry, the O2-consumption and the CO2-emission in the breathing air is measured and the basal metabolic rate is calculated from it (relatively complex).
Calculation of the fundamental metabolism with a formula
Already in 1918 J. A. Harris and F. G. Benedict published the “Harris-Benedict formula” named after them. In this formula, some influencing factors such as weight, height, age, and sex are included in the calculation of the basal metabolic rate. The formula is still a generally accepted, good approximation of the measured basal metabolic rate in nutritional medicine today:
For Men: Basal metabolic rate [kcal/24 h] = 66,47 + (13,7 × weight [kg]) + (5 × height [cm]) - (6,8 × age [years]) For women: Basal metabolic rate [kcal/24 h] = 655,1 + (9,6 × weight [kg]) + (1,8 × height [cm]) - (4,7 × age [years])
Here the difference of the first addend by almost a power of ten – 66.47 for men, 655.1 for women – stands out. This can be explained by the fact that the basal metabolic rate in men is more strongly determined by the body stature and the muscle mass dependent on it. Since the basal metabolic rate per kilogram body weight decreases with increasing body weight, the adjusted body weight should be used in the above formulas from a body mass index of 30 kg/m².
Calculation of the adjusted body weight
adapted weight [kg] = ideal weight [kg] + ((weight [kg] - ideal weight [kg]) × 0,25)
The ideal weight (according to Broca) is calculated here from body height in centimeters – 100. Apart from the calculation of the adjusted body weight, the ideal weight plays practically no role nowadays. The internationally standardized and recognized Body Mass Index (BMI) is used today to assess overweight and obesity, although it has also increasingly been the subject of criticism.
Other rules of thumb
simplified terms, and no longer suitable for everyday use in this day and age, the approximate assumption is that people consume 25 kcal per kilogram of body weight under today’s conditions. The following simplified formula is derived from this:
basic metabolic rate [kcal/ 24 h] = 25 × body weight [kg]
However, in numerous publications and by many specialist authors a somewhat different rule of thumb is used and the calculation is also differentiated according to gender. This is due to the following factors:
- Men are on average slightly taller,
- have more muscle mass (both absolute and relative to body weight)
have more muscle mass (both absolute and relative to body weight)
- and slightly less body fat as a percentage of body weight.
According to this rule of thumb, the daily basal metabolic rate (calorie requirement) is calculated as follows:
For men: Basal metabolic rate = [body weight in kg] x 24 x 1.0 For women: Basal metabolic rate = [body weight in kg] x 24 x 0.9
The multiplier 0.9 for women reduces the calculated value by 10%. The value 24 is used because the day has 24 hours. Both thumb formulas are too imprecise, as neither height nor age is taken into account. For this reason, they are also used as a basis for performance diagnostics such as a Spiroergometry or a lactate level tests and nutritional advice completely unsuitable!
Performance turnover (also work turnover or total energy turnover)
The actual energy requirement (calorie requirement) is calculated from the sum of basic and power consumption.
There are several calculation methods for estimating power consumption. The two most popular methods are PAL (= Physical Activity Level) and MET (= Metabolic Equivalent of Task).
The Physical Activity Level = PAL
With PAL (Physical Activity Level), the power consumption can be estimated by multiplying the calculated basal metabolic rate (GU) by a so-called activity factor (PAL).
- GU * 1.2: Exclusively sedentary or recumbent lifestyle: e.g. old and frail people
- GU * 1.3 – 1.5: Exclusively sedentary lifestyle without appreciably strenuous leisure activities: Precision mechanics, office workers
- GU * 1.6 – 1.7: Predominantly sedentary activity: motorist, laboratory assistant
- GU * 1.8 – 1.9: Predominantly walking or standing activity: Seller, housewife, craftsman
- GU * 2.0 – 2.4: Physically strenuous occupational work: construction workers, farmers
For sporting activities or strenuous leisure activities, an additional 0.3 PAL units per day can be added.
The Metabolic Equivalent of Task = MET
The MET method was developed by Barbara E. Ainsworth. It is used to calculate and compare the energy consumption of different activities (so-called “tasks”). Ainsworth defined 1MET as energy consumption (calorie requirement) of 1 kcal per kilogram of body weight per hour. Afterward, different activities were assigned correspondingly high METs.
Some excerpts from the current MET table
|Cycling 16 – 19,2 km/h||6.0|
|cycling 22,5 – 25,6 km/h||10.0|
|Running 8 km/h||8.0|
|Running 9,7 km/h||10.0|
|Running 12,1 km/h||12.5|
|Housework||2.0 – 4.0|
|Walking, 4,0 km/h||3.0|
The complete table contains over 600 entries. From home and garden work to professional activities to sports and leisure activities, hundreds of different activities are classified. At first glance complicated, however, a calculation of the power turnover is very simple and easy to apply.
The MET Formula
Before the formula is created, placeholders must be assigned to the values.
- The Metabolic Equivalent (MET) of a man (m) is described with 1.05 calories. The placeholder looks like this: 1 METm = 1.05 kcal
- And in a woman like this: 1 METf = 0.96 Kcal
- Each activity (task = t) is assigned a digit (MET). The placeholder is then like this: METt
The whole thing is now put together to a formula. For a man the formula looks like this:
METt * METm * Body weight in kg * (time in min. / 60) = Calorie consumption in kcal
A man of 82 kg body weight swims for 1 hour and 17 minutes chest. The METt (for activity) is taken from the table. In this case, the METt is 10.0. All these values are now inserted into the formula as follows:
10 * 1,05 * 82 kg * (77 min / 60) = 1104,95 Kcal
The same example for a woman weighing 56 kg:
10 * 0,96 * 55 kg * (77 min / 60) = 677,6 Kcal
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