BMI is a commonly used method for determining a healthy body weight which uses a calculation based on a measurement of weight in relation to height. A healthy BMI is said to be less than 25, and obesity starts at a BMI of 30.
It’s not a calculation I use for myself or for my clients because it’s flawed by not being able to make any distinction between the proportion of lean and fatty tissue in the body. An example of the failure of BMI is a rugby player who is relatively short in height in relation to his body weight. By using the BMI calculation, he may be classified as overweight, even obese, but when specific methods are used to assess his body composition, he could have a far greater proportion of lean muscle tissue to fat.
So a BMI calculation can’t identify either the proportion of fat in the body, or the location of fatty deposits, and yet fat distribution is a key factor in determining obesity associated health risks such as Type 2 diabetes, high blood pressure and heart disease.
Some Doctors believe that a more accurate predictor of long term health would be a waist measurement. Central fat is strongly associated with fat inside the abdominal cavity and around the internal organs which carries the greatest associated health risks.
So what is considered a healthy waist measurement? For men, a waist measurement greater than 40 inches would necessitate action. For women, the upper limit would be 35 inches.
I wouldn’t totally dismiss BMI because it can highlight a need to make lifestyle and dietary changes but, as a health professional, I’m far more interested in the overall proportion of body fat, as well as its location.