BMI is a screening number, not a diagnosis

The definition is right and easy to overread. Body mass index only combines weight and height. It does not measure body fat, and it cannot tell muscle from fat. Health agencies use it as a screening number for populations, not as a diagnosis for one person. The same value can mean different things for an athlete and for someone with less muscle. Read the sentence as the formula, then look at waist measure, body composition, and clinical context before treating the number as a verdict on health.