BMI is a common measure of healthy body weight, but it has some drawbacks.
BMI does not account for body composition, such as muscle, bone, and fat.
BMI can vary depending on age, sex, ethnicity, activity level, and other factors. BMI should be used with other methods to assess a person’s health, not as the only criterion.
BMI is not a direct measure of body fat, but a measure of excess weight. BMI can be inaccurate for people who have different body types or proportions of muscle and fat. For example, an inactive older person may have a normal BMI, but a high percentage of body fat. This is unhealthy, while a young athlete with a high BMI due to muscle mass may be healthy. According to the CDC:
Older adults usually have more body fat than younger adults with the same BMI. Women usually have more body fat than men with the same BMI. Muscular people and athletes may have high BMIs due to their large muscle mass.
For children and teens:
BMI can also be affected by factors such as height and sexual maturity in children and teens. BMI is more reliable for obese children than for overweight children, who may have more muscle or bone mass. BMI may also differ for thin children, depending on their body composition.
However, BMI is a good indicator of body fat for most people, about 90-95%. It can be used along with other measures to help determine a healthy body weight.