A single number we used to summarise people's health for a century. It is useful for population statistics — but it can be wrong about you specifically.
Where does BMI fail?
Because it does not account for body composition or fat distribution[1], and is unreliable for predicting body fat percentage since it cannot distinguish fat mass from fat-free mass[1].
In practice: a bodybuilder may be classified "obese", and a slim-looking person with high visceral fat may be classified "normal" — which is the more dangerous case.
high body fat percentage
risk
to body mass index
What is better?
Recent research indicates that body fat percentage and waist circumference predict mortality risk far better — especially cardiac death — than BMI[1]. People with high body fat percentages had nearly double the risk of dying from any cause and over triple the risk of cardiac death, even after adjusting for other health factors[1].
Including waist circumference via measures such as a body shape index and waist-to-BMI ratio also gave stronger predictive power for cardiovascular disease than BMI alone[2]. And waist circumference specifically correlates well with insulin resistance[3].
But — honestly
There is no consensus on a "healthy" body fat percentage for young adults as there is for BMI and waist circumference at the WHO, NIH and CDC[1]. So body fat percentage is conceptually more precise, but its reference points are less clear.
What to measure practically
- Waist circumference with a tape measure — the cheapest and most powerful measure available at home. Measure above the navel after a normal exhale, weekly.
- Comparison photos — every four weeks in the same lighting and pose.
- Clothing fit — trousers that have loosened or tightened are a real indicator.
- Training performance — a weight you lift or a distance you walk.
- And don't scrap the scale — use it as a weekly average, not a daily number (why it fluctuates).