Medical significance and history of the indicator
Body Mass Index (BMI, or BMI from English Body Mass Index) is a basic diagnostic indicator that allows you to assess the degree of correspondence between a person’s weight and his height. Using this value, doctors, nutritionists and fitness trainers determine whether the mass is insufficient, normal or excessive, which directly affects the risks of developing various pathologies.
The indicator was developed back in 1832 by the Belgian mathematician and sociologist Adolphe Quetelet. Despite its age, Quetelet's formula is still the official gold standard of the World Health Organization (WHO) for primary screening of the population for obesity or dystrophy.
⚖️ Расчет индекса массы тела
Mathematical formula for calculations
No complex tools are required to manually calculate BMI. The indicator is calculated by dividing body weight in kilograms by the square of height, expressed in meters.
Step-by-step calculation example:
Let's assume that a person is 175 centimeters tall and weighs 75 kilograms.
1. Convert height to meters: 175 cm = 1.75 m.
2. Square the height: 1.75 × 1.75 = 3.0625.
3. Divide the weight by the resulting value: 75 / 3.0625 = 24.48.
Result: BMI is 24.5 kg/m².
Official WHO classification of values
The resulting figure must be checked against the international scale. The World Health Organization identifies six main categories of body condition. It is important to note that this table applies only to adults (over 18 years of age).
| BMI indicator | Body weight category | Risk of comorbidities |
|---|---|---|
| Less than 18.5 | Mass deficiency (underweight) | Increased (risk of anemia, osteoporosis) |
| 18.5 - 24.9 | Normal weight | Normal (minimal) |
| 25.0 - 29.9 | Overweight (pre-obesity) | Elevated |
| 30.0 - 34.9 | I degree obesity | High |
| 35.0 - 39.9 | Class II obesity | Very tall |
| 40.0 and more | Degree III obesity (morbid) | Extremely high |
Limitations of the method and uncertainty
For all its simplicity and universality, Quetelet's formula has significant limitations. BMI evaluates only overall mass, without taking into account the ratio of fat, muscle and bone tissue in the body. Because of this, the indicator may be inaccurate in a number of cases:
- ▪ Professional athletes. Weightlifters, bodybuilders and wrestlers have a huge amount of dense muscle mass. Their BMI is often in the “Obesity I or II” zone, although the percentage of fat in their body is minimal and their health is normal.
- ▪ Elderly people. With age, a person naturally loses muscle mass, which is replaced by fat. An elderly person's BMI may be in the green "Normal" zone, but in fact he may have hidden (visceral) obesity.
- ▪ Pregnant women. During the gestation period, calculating the index using the classical formula completely loses its medical relevance.
Additional diagnostic methods
In modern clinical practice, BMI is rarely used in isolation. To get an accurate picture, doctors additionally measure the waist circumference (the norm for men is up to 94 cm, for women - up to 80 cm) and calculate the ratio of waist circumference to hip circumference. Bioimpedansometry is considered the most accurate method for determining body composition today.