The BMI has the immense advantage of being simple. But this simplicity is also its weakness: by reducing corpulence to a weight/height ratio, it misses many elements. Understanding its limits allows you to use this index wisely, without making it say more than it can.
1. He ignores body composition
BMI does not differentiate between muscle and fat. However, these two tissues do not have the same role or the same impact on health. Two people of the same BMI can have very different body compositions, one muscular, the other not.
2. It says nothing about fat distribution
The location of the fat matters more than its overall quantity. Abdominal fat (around the organs) is more harmful than fat distributed on the hips and thighs. BMI, on its own, does not capture this essential distinction.
| Indicator | What it offers in addition |
|---|---|
| Waist | Fat abdominal |
| Waist/hip ratio | Fat distribution |
| Fat mass measurement | Body composition |
3. It varies according to age and profile
BMI thresholds are not suitable for everyone. In the elderly, a slightly higher BMI may be protective. In athletes, it overestimates fat. In children, growth curves must be used.
4. Health is not reduced to a number
Beyond body size, physical condition, diet, sleep, smoking, blood pressure or blood sugar levels determine health. You can be metabolically healthy at different BMIs, and vice versa.
The BMI remains useful as a first benchmark, but it always benefits from being supplemented by a global assessment carried out with a professional.
💡 tips to remember
- BMI does not distinguish muscle from fat: two people with the same BMI can have very different body compositions.
- The distribution of fat matters more than its quantity: abdominal fat is more harmful than that of the hips and thighs.
- The waistline usefully completes BMI by providing information on abdominal fat.
- BMI thresholds are not suitable for everyone: they vary according to age, and do not apply to children or muscular athletes.
- You can be in good metabolic health at different BMIs: health cannot be reduced to a number and benefits from being assessed globally.
