Body Mass Index (BMI) is a ratio of weight to height. It has been used to group people as underweight, “normal” weight, overweight, or obese. While it is a useful public health tool, BMI’s ability to predict health risks on an individual level has recently been questioned.
An analysis of national health survey data concluded that a BMI in the “overweight” range (22.5 to 29.9 kg/m2) was not associated with a higher risk of death, especially in older adults.
The study analyzed data on over 554,000 adults with an average age of 46 years. Being underweight (BMI less than 18.5 kg/m2) or obese (30 kg/m2 or higher) was generally associated with higher risk of death in the nine to 20 years of follow-up. The relationship between overweight and risk of death, however, was inconsistent.
The authors concluded the clinical value of BMI on an individual level has limitations.
BMI does not account for differences between sexes and genders, across the lifecycle, and, importantly, across racial/ethnic groups. Body shape and composition vary among racial and ethnic groups. The BMI scale is based primarily on data collected from non-Hispanic White populations.
The American Medical Association (AMA) has concluded that BMI is an imperfect way to measure body fat and health risk. They suggest physicians use BMI in conjunction with other valid measures of risk, such as waist circumference, measurements of visceral (belly) fat, genetics, and metabolic factors.
You and your healthcare provider should not ignore your BMI, but it should be only one tool of many when determining risk for conditions like cardiovascular disease and type 2 diabetes.