The merits of using BMI as an indicator of body fat and obesity are still contested. A key contention to the use of BMI indicators is that it provides a measure of body mass/weight rather than providing a direct measure of body fat. Whilst physicians continue to use BMI as a general indicator of weight-related health risks, there are some cases where its use should be considered more carefully14:

• muscle mass can increase bodyweight; this means athletes or individuals with a high muscle mass percentage can be deemed overweight on the BMI scale, even if they have a low or healthy body fat percentage;
• muscle and bone density tends to decline as we get older; this means that an older individual may have a higher percentage body fat than a younger individual with the same BMI;
• women tend to have a higher body fat percentage than men for a given BMI.

Physicians must therefore evaluate BMI results carefully on a individual basis. Despite outlier cases where BMI is an inappropriate indicator of body fat, its use provides a reasonable measure of the risk of weight-related health factors across most individuals across the general population.