How to find body mass index: ideal weight formula

Body mass index (BMI) is a mathematical expression that gives an idea of ​​the ratio of body weight and height of a given person. This index was first introduced by the Belgian mathematician and statistician Adolph Quetelet, therefore it is also called the Quetelet index. How to find the body mass index is described in this article.

BMI and its calculation formula

How to find body mass index? The answer to this question will be a simple mathematical formula, which has the form: BMI = body weight / height ² . In this formula, body weight is expressed in kilograms, and a person’s height in meters. Thus, the BMI dimension is kg / m ² in the international SI unit system.

BMI Interpretation

After it became known how to find the body mass index, it must be interpreted. It should be noted that BMI for a particular person is not a constant, but changes throughout life. This characteristic also depends on the ratio of the amount of adipose tissue and the number of muscles in the body.

If the person is an adult, then you should use the special table provided by the World Health Organization to determine the ratio of your height and weight.

All people should be guided by the figures provided, regardless of gender and age, provided that they are older than 18 years.

However, today there is a lot of debate regarding the correct interpretation of BMI and the rationality of its use for assessing human health.

Incorrect rating for tall and low people

Knowing how to find the human body mass index, one can notice that the mass enters the formula linearly, while the growth in the formula is squared. Considering that body mass grows proportionally to the cube with increasing body growth, since it depends on a three-dimensional value - body volume, then according to the BMI calculation formula, it turns out that higher people will have higher BMI values, but will also have the same shape and relative body parameters that low people.

The above mathematical formula, which answers the question of how to calculate the body mass index (BMI), adds about 10% to the BMI value for tall people and reduces the same percentage of BMI for low people. In other words, a person with a short stature and excess adipose tissue, according to BMI, will have a healthy weight. On the contrary, a tall person with a normal content of adipose tissue, according to BMI, will be classified as an individual who is overweight.

Muscle and fat tissue

The formula for calculating BMI, and the table that gives approximate figures for the interpretation of this formula, do not take into account the real distribution of adipose and muscle tissue in the human body. As a rule, BMI overestimates body fat in people with high body weight, such as athletes, and underestimates excess fat in people who are low in weight.

So, in 2008, a study was conducted in the United States, which calculated a BMI of 13 601 volunteers. According to the results of this study, 21% of men and 31% of women from the studied people had obesity (BMI> 30). However, according to the percentage of body fat in the body, obesity was observed in 50% of men and 62% of women.

It should also be noted that according to the anatomy, women naturally accumulate more adipose tissue in the body than men. Moreover, the answers to the questions of how to find the body mass index for women and how to interpret it will be exactly the same as for men, according to the general concept of BMI, which is not entirely correct, and for the weaker sex the tabular data should be adjusted in side of their increase.

Calculation for a child body mass index

It should be noted that the calculation of body mass index (BMI) for children and adults cannot be interpreted using the same criteria, since children and adolescents are actively growing, and their body is in the process of formation. Due to the different anatomy of men and women, the same BMI results cannot be interpreted. Thus, the indicator must be interpreted taking into account the gender and age of the person.

How to find the body mass index for a child, and how to interpret it correctly? It should be said that after the indicator is calculated for a child according to the same formula as for an adult, and after the age group to which this child belongs is determined, the obtained BMI value must be compared with the table of corresponding values ​​for boys and girls, respectively. The table for each age group of children shows the data in percentiles. The percentile is the relative value of the scatter of the indicators of any characteristic (in this case, BMI), that is, knowing the BMI of the child and his age, you can determine how many children of his age have a larger indicator, and how much less.

Also in these tables are used concepts such as underweight, healthy weight, overweight and obesity, depending on the area in which a person’s BMI lies.

BMI and human health

A study published in 2005 in one of the American magazines showed that those who are overweight have the same risk of dying as people with normal body weight according to BMI estimates. At the same time, people who are obese or severely underweight have a higher risk of dying.

In 2010, another study was completed, in which 11,000 people were monitored for 8 years. According to the results of this study, BMI is a poor indicator for assessing the risk of heart disease and myocardial infarction. A more acceptable value for assessing these risks is the ratio of growth and circumference at the waist. For women, the ratio of circles in the waist and hips is also a good indicator of overweight or normal weight.

Thus, BMI is an approximate mathematical value for assessing normal, healthy body weight. Each person must understand and consider a number of factors for the correct interpretation of the obtained value of this index.