Nutrition
BMI: when it works, when it misleads, and what to pair it with
BMI is useful as a screen, but it misleads in athletes, older adults, and pregnancy. Here is when to apply it and what metrics to combine.
Body mass index (BMI) is the best-known anthropometric metric in the world — and also the most misunderstood. It works reasonably well as population screening, but it stops being informative as soon as high muscle mass, sarcopenia, edema, or pubertal development enters the picture.
When BMI is useful
- Healthy adults aged 19 to 65, sedentary or moderately active.
- Large-scale epidemiological comparisons.
- Initial screening before requesting body composition or skinfolds.
When BMI misleads
- Athletes with high muscle mass — a BMI of 28 can coexist with low body fat.
- Older adults with sarcopenia — a normal BMI can hide significant lean mass loss.
- Pregnant or breastfeeding clients and children: use specific curves.
- People with edema or ascites: weight reflects fluid, not tissue.
What to combine BMI with
For a useful clinical read, combine BMI with waist circumference, waist-to-hip ratio, and — when possible — body composition via bioimpedance or skinfolds. Visceral fat matters more than total weight for cardiometabolic risk.
Frequently asked questions
Why does the healthy BMI range end at 24.9?
It is a population cutoff based on mortality: above that value, cardiometabolic risk starts to rise in cohort studies. It is not an exact biological threshold at the individual level.
Can BMI diagnose obesity?
Not on its own. Obesity is defined by excess fat mass with clinical impact; BMI is a screen, not a diagnosis.
About the author
Equipo Almendra
Editorial · Almendra
The Almendra editorial team brings together nutritionists, engineers, and product managers writing about how to run a modern nutrition practice.
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