What is body mass index and is it worth considering

What is Body Mass Index

Body mass index (BMI, Body Mass Index, BMI, Quetelet index) is the ratio of height to weight. BMI helps to find out whether a person has enough fat, whether it is time to lose weight or, conversely, gain weight, and is calculated by the formula:

BMI = weight (kg) / height² (m)

Next, you need to look at the value in the table. The World Health Organization (WHO) BMI Nutritional status has established the following indicators for people over 20 years old:

Height to weight ratio	Body mass index
Underweight	less than 18.5
Norm	18, 5–24, 9
Preobesity	25–29, 9
Obesity I degree	30–34, 9
Obesity II degree	35–39, 9
Obesity III degree	more than 40

For children and adolescents, the exact values depend on the age. The standards for people 5-19 years old can be found on the WHO website.

Why Know Body Mass Index

It is used to find out the risks of diseases. The WHO claims the Mean Body Mass Index (BMI) that being overweight increases the risk of type 2 diabetes, coronary heart disease, breast, uterine, bowel, prostate, kidney and gallbladder cancer.

Over the year, on average, overweight in the world is associated with 2.8 million deaths and 35.8 million disabilities.

WHO believes that for good health, everyone should strive for an index of 18, 5-24, 9. The risk of disease increases between 25 and 29, 9, and after 30 it increases significantly.

Who came up with the idea of calculating body mass index

The formula itself was derived by Adolphe Quetelet (1796-1874) - the average man and indices of obesity in 1832 by the Belgian astronomer, mathematician and statistician Adolphe Quetelet. But it became known only 140 years later, after the study of Indices of relative weight and obesity by physiologist and obesity specialist Ansel Keys. He analyzed the parameters of 7,400 people from five countries and compared different formulas for determining excess weight. It turned out that BMI, for all its simplicity, most accurately predicts overweight and obesity.

This opened up great opportunities for large-scale research. Scientists no longer need to measure the amount of fat in expensive and complex ways: they can quickly calculate the indices of hundreds of people, including those from past decades, and draw conclusions.

However, such methods are not always suitable for individuals. After all, when it comes to health, you want to get true values, and not some average numbers.

How accurate is body mass index?

Despite the fact that BMI is still widely used in medicine, there is more and more evidence of its inaccuracy. Here are some facts that prove that body mass index is not the best way to know if you are overweight or not.

BMI does not show the actual percentage of fat and muscle

The formula is too simple. Thus, the BMI of a muscular athlete may coincide with the index of an obese untrained person. They will weigh the same, but the percentage of fat, appearance and health risks are very different.

This was confirmed by the Body Mass Index as a Predictor of Percent Fat in College Athletes and Nonathletes study of 439 people. The body mass index of athletes and untrained men often showed overweight when they were not. Women with extra pounds, on the contrary, were within the normal range.

Similar results were obtained in the large-scale study Accuracy of Body Mass Index to Diagnose Obesity In the US Adult Population, involving 13 thousand people. The scientists compared the body mass index value and the actual percentage of body fat obtained using bioimpedance analysis. BMI showed obesity in 21% of men and 31% of women, and analysis - in 50% of men and 60% of women.

Body mass index is wrong about half of the time, soothing overweight people.

BMI does not take into account gender and age

The framework of the index was made universal to make it easier to conduct large-scale research. At the same time, the amount of fat in women and men differs by an average of 10% Sex differences in human adipose tissues - the biology of pear shape, so it is wrong to apply the same values for both sexes.

In addition, the proportions of muscle and adipose tissue in the body change. With age, the metabolism slows down, the breakdown of muscle tissue and the deposition of adipose tissue begins. Therefore, for correct conclusions, it is necessary to take into account both the sex and the age of the person.

BMI does not take into account the three-dimensionality of a person

Professor Nick Trefenten of the University of Oxford has questioned the current BMI formula. The scientist claims that it does not take into account the real features of the human physique and gives inaccurate data, since changes in height and weight occur non-linearly. It shows short people that they are slimmer than they are, and makes tall people believe that they are thicker.

Trefenten advised a new calculation method, which, in his opinion, will give more correct results.

BMI = 1.3 * weight (kg) / height ^{2, 5} (m)

At the same time, the professor believes that any formula will be imperfect, since a person is too complex.

Are there alternatives to body mass index

Typically, BMI is considered to determine health risks. But some researchers say Waist-to-height ratio as an indicator of 'early health risk': simpler and more predictive than using a 'matrix' based on BMI and waist circumference, that waist circumference or waist-to-hip ratio is much better for this. …

The fact is that fat around the liver and other abdominal organs (also called visceral fat) is considered the most dangerous. It possesses high metabolic activity Health consequences of visceral obesity: it produces fatty acids, inflammatory agents and hormones that increase the level of low-density cholesterol, glucose and triglycerides in the blood, and increase blood pressure.

The study Abdominal obesity and the risk of all-cause, cardiovascular, and cancer mortality: sixteen years of follow-up in US women with the participation of 44 thousand women showed a clear connection between waist circumference and various diseases. Girls with a BMI within normal limits, but with a waist circumference above 89 cm, were three times more at risk of dying from heart disease than participants with lower indicators.

Similar data were obtained in the Shanghai study of Abdominal adiposity and mortality in Chinese women: excess fat deposition on the abdomen increased the risk of death, regardless of BMI.

The International Diabetes Organization considers The IDF consensus worldwide definition of the METABOLIC SYNDROME healthy waist circumference up to 80 cm for women and up to 94 cm for men.

According to the WHO Waist Circumference and Waist-Hip Ratio Report of a WHO Expert Consultation GENEVA, 8-11 DECEMBER 2008, values above this norm increase the risk of cardiovascular disease, type 2 diabetes, metabolic syndrome and hypertension. And starting from 88 cm - for women and 102 cm - for men it becomes even more significant.