The BMI is a useful measurement for most people over 18, and can help to assess if people are overweight or obese.

Your BMI may not always be an entirely accurate representation of carrying excess fat, including:

  • When pregnant, or having recently given birth, and/or nursing
  • Having muscular or athletic build

In these examples body weight and BMI may be higher for reasons other than excess body fat, and therefore BMI would be a less useful indicator of health.

Also, BMI does not distinguish between body fat and muscle mass, which is why muscular athletes may have a high BMI because of increased muscle rather than additional body fat.

Is BMI reliable as an indicator of body fat?

BMI can be useful as a rough guide, and there is a correlation between BMI and body fat, however it is also dependent on sex, race and age.

At the same BMI level, men tend to have less body fat than women, while older people generally have more body fat than younger adults, on average.

Another simple measure to assess body fat and health risk is waist circumference.

Guidelines from the National Heart, Lung and Blood Institute recommended looking at waist circumference – as abdominal fat can lead to obesity-related diseases – and other risk factors associated with obesity such as physical inactivity and high blood pressure

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