What is BMI?
The Body Mass Index assesses the balance between a person's weight and height. It is commonly used to assess the health risks associated with being underweight or overweight. A high BMI can be correlated with high body fat, although this may not always be accurate in certain cases, such as in athletes or the elderly. In fact, BMI does not directly measure body fat and does not diagnose health status.
How do I calculate my BMI?
The body mass index is obtained using a basic formula: weight in kilograms divided by height in meters squared.
\[ IMC = \frac {weight (kg)}{height (m)^2} \]
Example: A person weighing 68 kg and measuring 1.80 m would have a BMI of \( BMI = \frac {68}{1.80^2} \) = 21, i.e. a normal corpulence.
Interpreting BMI
According to WHO classifications, BMI can be broken down as follows:
- Less than 18.5: underweight
- 18.5 to 25: Normal weight
- 25 to 30: Overweight
- 30 to 35: Level 1 or moderate obesity
- 35 to 40: Level 2 severe obesity
- Over 40: Level 3 morbid obesity
These classifications provide a better understanding of the potential impact of weight on health. They do not apply to children, adolescents, pregnant women, athletes or people over 65. These populations require specific evaluation using adapted tools.
For an in-depth, personalized assessment, we recommend consulting a physician.
BMI limitations
Despite its recognized usefulness, BMI is not a perfect measurement tool, and has a number of limitations that must be taken into account:
- Body composition: BMI does not differentiate between the weight of muscle and fat. A muscular person can have a high BMI without excess fat (high muscle mass).
- Age and sex: Natural variations in body composition according to age and sex are not taken into account.
- Fat distribution: BMI does not reflect the distribution of body fat, particularly abdominal fat, which is a major risk factor.
Using BMI in practice
Although imperfect, BMI remains a practical and reliable indicator for a number of uses:
- Screening: Identify individuals at risk of weight-related diseases.
- Monitoring: Evaluating the effectiveness of nutritional interventions or weight-loss programs.
BMI is a simple, accessible tool for assessing weight and associated health risks. However, it must be used in conjunction with other medical measurements and assessments for a complete analysis of an individual's health.