Body mass index (BMI) is a measure of body fat based on height and weight that applies to adult men and women. BMI does not measure body fat directly, but research has shown that BMI is a reliable indicator of body fatness for most people. BMI can be used to screen for weight categories that may lead to health problems but it is not diagnostic of the body fatness or health of an individual. The vast majority of research indicates that BMI is associated with a range of health risks, including premature death, diabetes, heart disease, stroke, and cancer. However, there is some debate about whether BMI is the best measure of these risks, and whether it should be used as a screening tool.
BMI is calculated by dividing a person's weight by the square of their height. The BMI ranges are as follows:
Underweight: BMI of less than 18.5
Normal weight: BMI of 18.5 to 24.9
Overweight: BMI of 25 to 29.9
Obesity: BMI of 30 or more
Obesity can further be classified as follows: Class 1 obesity: BMI of 30 to 34.9. Class 2 obesity: BMI of 35 to 39.9. Class 3 obesity: BMI of 40 or more.
The World Health Organization (WHO) defines overweight and obesity as "abnormal or excessive fat accumulation that presents a risk to health." A BMI of 25 to 29.9 is considered overweight, and a BMI of 30 or more is considered obese. A BMI of 40 or more is considered morbidly obese.
What Are the Pros of Using BMI to Measure Health?
What Are the Cons of Using BMI to Measure Health?
Should BMI Be Used to Measure Health? BMI is a useful tool to measure health risks associated with overweight and obesity, but it has limitations. For example, it does not account for differences in muscle mass, bone density, or body fat distribution. Additionally, people who are very muscular or have a lot of bone mass may have a high BMI without having a high body fat percentage. Furthermore, BMI does not measure visceral fat, which is the type of fat that surrounds your organs and is linked to an increased risk of heart disease and other chronic health conditions.
BMI should not be used as the sole criterion for diagnosing overweight or obesity. Other measures of body fat, such as waist circumference, skinfold thickness, and DXA scan, should be considered. BMI should be used in conjunction with other health risk factors to make decisions about treatment and prevention.