Basal metabolic rate
The basal metabolic rate, also called basal metabolic rate is a variable which is used to characterize the metabolism mainly in humans: it is the quantity of energy that the body per day at complete rest, with indifference temperature ( 28 ° C) and sober ( ie needed. empty stomach ) to maintain its functions.
Introduction
Physically, this is the basal metabolic rate of work per time, so power than the SI unit officially the watts ( = joules per second) is defined. In practice, however, is usually further calculation instead of joules with the outdated unit calories and the basal metabolic rate - as it always thus refers to 24 hours on a full day - accordingly, in kilocalories per 24 hours ( kcal/24 h) given ( which also is the reference " / h 24 " is often omitted again ).
The conversion rate between kilojoules and kilocalories there are - depending on the definition of standard conditions - slightly different factors. The 9th General Conference on Weights and Measures adopted in 1948 following conversion factor:
Factors that affect the basal metabolic rate, are not limited to: age, gender, body weight, height, muscle mass, thermal insulation by clothing as well as the state of health (eg at elevated body temperature due to fever or the like. ).
Measurement
Through methods of calorimetry can be the reason sales directly from the amount of heat dissipated or indirectly via the oxygen consumption measure, but this is too expensive for everyday life outside of scientific research, for example in hospitals.
The direct calorimetry was developed in the 18th century by Antoine Laurent de Lavoisier, however, has now only of historical significance. Instead today, as measured in the practice of medicine with spirometers the respiratory flow of the subject and determines the volume of the respiratory air, and the oxygen consumption of both, including the basal metabolic rate itself.
Calculation using approximate formulas
Harris -Benedict formula
Already published in 1918 JA Harris and FG Benedict named after them Harris -Benedict formula, go down in the body mass, the size and age as factors influencing basal metabolic rate.
The formula is still one in which nutritional medicine generally accepted good approximation of the measured BMR Represent is for men:
And for women
In legal units, leading to the result in the SI unit kJ per day, are the formulas for men:
And for women:
The striking difference of the first summand by almost an order of magnitude expresses that the basal metabolic rate in men is more strongly influenced by the stature and its dependent muscle mass.
Broca's index adjustment
Since with increasing body fat percentage decreases the metabolic rate per kilogram of body weight should primarily from a BMI of 30 kg / m² a corrected body weight are used in the formulas above, the taking into account of normal weight after Paul Broca calculated as follows:
A simplification arises if both formulas are summarized. This gives the corrected basal metabolic rate without a corrected body weight must be used.
The formula for men
And for women
In legal units, leading to the result in the SI unit kJ per day, are the formulas for men:
And for women
Except for the calculation of the corrected basal metabolic rate nowadays practically the normal weight according to Broca no longer plays a role and is the assessment of overweight and obesity by body mass index, as well as various other physical parameters have been replaced.
Mifflin - St.Jeor formula
A newer formula was proposed in 1990 by Mifflin and St.Jeor, which will bear the lifestyle changes of the last financial statements 100 and an average of about 5% is more accurate.
With s = 5 for males and s = -161 for women.
In legal units, leading to the result in kJ per day, the formula is:
With s = 20.93 for men and s = -674.08 for women.
Simple estimation
Greatly simplified, but still suitable for everyday use, is the approximate assumption that under the stated conditions of the human per kilogram of body weight consumed 25 kcal per day. This yields the following simplified formula is derived:
Since both day 24 hours and has 100 kJ correspond approximately 24 kcal, in numerous publications even simpler empirical formula is used by a factor of 24. Thus, far from the hundred times the weight of the BMR one day in kilojoules and from the weight of even the basal metabolic rate in kcal per hour. According to this rule of thumb, the daily basal metabolic rate calculated for a man as follows:
Since men are on average slightly larger and in proportion to body weight have both more muscle mass and less body fat than women, a lump sum is assumed to be 10% lower basal metabolic rate in women:
This results in a person with a weight of 70 kg approximately the following values:
Actual energy sales
With increased physical activity and energy expenditure increases, and the resulting per day in addition unreacted amount of energy is called power sales. The actual energy sales ( as the sum of basic and advanced sales) can be estimated by multiplying the previously determined BMR by an activity factor. This amounts to between 1.2 lying down or sitting up and about 6 in some cases even much higher in heavy physical work, such as in heavy industry, in sports. For office work, however, only one comes to an activity factor of 1.3 to 1.6.
In case of illness of the basal metabolic rate to determine the actual energy needs except with the activity factor ( the mobilized in bedridden patients 1,2 and in patients 1.3 is ) also multiplied by a trauma factor, which is determined by the severity of the disease and between 1, 0 and 1.6.
The heat output of a person at rest is on average around 90 watts, it produces about 15 liters of carbon dioxide per hour and per day also sweaty about 1 to 2 liters of water, which corresponds to a cooling capacity of 26-52 watts.
Basal metabolic rate in humans
The largest share in the turnover in the human body have liver and skeletal muscle, each with about 26 %, followed by brain with 18%, the heart with 9% and the kidneys with 7%. The remaining 14 % is held by the other institutions.