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Own body weight is a relevant issue for most people. While some are struggling with excess weight, others are exploring what could be the cause of unnatural thinness. But what body weight can be generally considered normal for a particular person? A simple and popular formula will help, albeit inconclusive, to resolve this issue.
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What is Body Mass Index?
This concept can be found in the form of abbreviations BMI, BMI or phrases Body Mass Index, Quetelet index. It allows you to assess the degree of correspondence between the mass of a person and his height. Due to this, it is possible to understand whether a person’s weight is normal, overweight or underweight. BMI indicators are often taken into account when determining the indications for treatment. This value is calculated using a simple formula:
BMI = weight / height²
where body weight is measured in kilograms and height in meters.
The World Health Organization has developed a special table for interpreting the indicators of people over 20 years old:
|
Height to weight ratio |
Body mass index |
|
Lack of body weight (deficiency) |
less than 18.5 |
|
Norm |
18.5-25 |
|
Overweight, overweight |
25-30 |
|
Obesity |
30–35 |
|
Severe obesity |
35-40 |
|
Very severe obesity |
more than 40 |
In children and adolescents, the exact values depend on age. The norms for them can be found on the WHO website.
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Who came up with the idea of calculating the body mass index?
The body mass index formula was invented by the Belgian astronomer, mathematician, statistician and sociologist Adolphe Quetelet back in 1869. However, the concept gained wide popularity only 100 years later, thanks to the research of the physiologist and obesity specialist Ansel Keys. This scientist studied the parameters of 7,400 people and 5 countries, trying to find a universal and optimal formula for determining excess weight. It turned out that a simple BMI variant best defines obesity.
This formed the basis for further large-scale research. Scientists no longer needed to use expensive and complex ways to measure body fat. It was enough to calculate the indices of several hundred people from different times and draw certain conclusions based on this. Of course, the method is not suitable for everyone. When we talk about health, everyone wants to know specific numbers for themselves, and not general average parameters.
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Why do you need to know the body mass index?
Body mass index allows you to determine the risks of certain diseases. WHO suggests that being overweight increases the likelihood of type 2 diabetes, coronary heart disease, and cancer. Overweight causes 2.8 million deaths and 36 million disabilities worldwide each year. WHO recommends that each person stick to their body index in the range of 18.5 – 25 points. Above this mark, the risk of disease increases, and after 30 it increases even more significantly.
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The accuracy of BMI-based predictions
And although the index is often used in medicine, there is more and more information about its inaccuracy. Several facts can be cited that cast doubt on the choice of a formula as the best tool for determining excess weight.
1. BMI does not measure the actual percentage of muscle and fat
The disadvantage of the formula, as well as its advantages, is simplicity. As a result, the BMI of a muscular athlete may coincide with that of an obese untrained person. Given the same height and weight, body fat percentage, appearance, and therefore health risks can vary considerably. Studies of hundreds of people have shown that athletes were often overweight, and women who were clearly overweight were within the normal range.
Similar information was shown by another study of 13 thousand people. Using bioimpedance analysis, the scientists compared BMI with real body fat percentage. The index showed obesity in 21% of men and 31% of women, while a more accurate scientific analysis – in 50% of men and 60% of women. We can say that in about every second case, the body mass index gives the wrong information, calming an overweight person.
2. BMI does not take into account gender and age
For large-scale research, the index frames were deliberately made universal. But here the volumes of fat in men and women differ by about 10%. Is it correct to apply the same criteria for different genders?
Age changes the proportions of muscle and adipose tissue in the body. Over time, metabolism slows down, muscle tissue begins to break down, and fatty tissue begins to accumulate. Correct conclusions require taking into account both the sex of the person and his age. According to statistics, BMI in men is higher than in women.
3. BMI does not take into account the three-dimensionality of a person
Oxford professor Nick Trefenten also questioned the capabilities of the BMI formula. According to the scientist, it does not take into account the real features of the structure of the human body. In it, height and weight do not change linearly. As a result, the formula considers short people more slender, and tall people more dense. Trefenten adjusted the formula so that it gives the correct results:
BMI = 1.3 × weight / height2.5,
where body weight is measured in kilograms and height in meters.
Nevertheless, the creator of the formula himself considers it imperfect, like any in general – the human body has a too complex structure and shape.
4. Change in BMI rate
Over the past 30 years, the “normal” body mass index has changed several times. If before 1998 in America the threshold was 27.8 kg / m2, then after 1998 doctors began to consider 25 kg / m2 as such. A small change in the standard led to the fact that immediately 29 million Americans were considered to be overweight.
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Body Mass Index Alternatives
BMI is calculated to identify health risks. However, some researchers believe that it is much better to use measurements of waist circumference or waist-to-hip ratio. Fat collected around the liver and abdominal organs is considered the most dangerous. He has a high metabolic activity. This substance produces fatty acids, hormones, inflammatory agents, which increases the level of lean cholesterol, blood glucose, and blood pressure.
American studies involving 44 thousand women have shown that there is a direct connection between waist circumference and various diseases. Even if the BMI is within normal limits, and the waist circumference is above 89 centimeters, the risk of death from heart disease is three times higher than that of women with normal, lower indicators.
Similar data were obtained in Shanghai – excess fat in the abdomen increases the risk of death, regardless of the BMI index. The International Diabetes Federation considers a normal waist for women up to 80 centimeters, and for men – up to 94 centimeters. According to the WHO, exceeding this norm leads to the emergence of risks of cardiovascular diseases, type 2 diabetes and hypertension. If the waist is more than 88 centimeters for women and over 102 centimeters for men, the risks become even more significant.
Other indices are used to determine normal body weight: Brock, Breitman, Noorden, Tatonya, Bernhard, Davenport. Basically, they are based on all the same height and weight data.
See also:
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