Body Mass Index (BMI) Fact Sheet
The Origin of BMI
The Body Mass Index is a old formula. Invented by the Belgian mathematician Adolphe Quetelet in the 19th century. This means, it has the same older as the formula by Paul Broca. The is the old method, simply substitute 100 of size in cm to get the normal weight Later this was reduced by 10% to get ideal weight.
Body size = 180 cm
Normal weight = 180-100 = 80 kg
Ideal weight = 80 – 10% = 72 kg
The Broca-Formula, named by Paul Broca, a French doctor for the military, is very simple and everybody can calculate it without problems. Everybody born before 1975, can remember this formula, because it was used in his childhood.
But there is a problem with the Broca-Formula. When you need to compare a big group of humans, you need one value which can compared with others. So the BMI is perfect for this size and weight together in one reference number.
Alternative to BMI
It would be much better to use the real fat rate. But this is much complicated and only high-tech medical equipment can make it exact. The simple solution in body fat scales with electric power is quite inaccurate This is the reason of taking the BMI as simple value. Also in telephone interviews the people can be asked for size and weight and the BMI can calculated.
The Body Mass Index is calculated by the following formula:
body weight in kilogram divided by body height in meter to the second
BMI = x KG / (y * y) M
x=body weight in KG
y=body height in M
Online BMI Calculator
The simplest way to calculate the BMI is using an online calculator. Check it out: Body Mass Index (BMI) Calculator.
BMI Classification Table
This is the official classification of the Body Mass Index from the WHO.
|Obesity III||≥ 40|
This classification is good for science however this classification of one single person isn’t perfect. For example, there is no matter of sex or age. But there are classification, which take care of this. Here is the table of National Research Council (NRC) from 1989:
The formula of calculating the BMI is the same as for adult people. But the meaning is different.
A team of scientists (K. Kromeyer-Hauschild, M. Wabitsch, D. Kunze et al.) has taken 2001 the values of a big amount of boys and girls. These shows the spreading of the Body Mass Index with age as reference.
The charts have the age from left to right and the BMI from bottom to top.
You see Percentil-Lines in the chart. P50 means, that 50% of the kids have a higher and 50% have a lower BMI. P3 means, that 3% of the kids have a lower BMI.
Overweight is from P90 and higher. This means, 10% of the kids are overweight. Underweight is lower than P3. In the charts above the areas are colored in red. Normal weight is with green color. This borders are more to fit for scientists needs and less for the child.
A real problem is the BMI for sportsmen. Muscles have more weight than fat. So they get a very high BMI, but this doesn’t mean, it is a health problem.
Calculation & The Reason:
The BMI calculates mass per surface. To calculate the surface the size will be multiplied with itself. This is a correct formula for a square, but not for a human.
The Body Mass Index is only a number. The strict meaning of the WHO doesn’t take care about age or other. Sportsmen get very quick a BMI over 25 and are overweight, when trusting the BMI.
This are two males’ body with the same BMI. The left one got much muscle mass, the right one has more fat. In this case the BMI doesn’t inform about the fitness of the man.
The health of someone should not be checked simply by it’s BMI. If a butcher will calculate the fat of a pig with BMI, he will lose his licence. A real health problem is in visceral fat. But the BMI doesn’t care about it.
When someone has a BMI over 40, its sure that he is overweight and will get some problems with health.
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“A healthy body, for a beautiful lifestyle!”