Limitations of the BMI

Whilst the BMI score can tell a person if they are carrying too much weight, but it cannot tell if they are carrying too much fat.

Importantly, BMI cannot tell the difference between excess fat, muscle mass or bone mass.

The adult BMI score does not consider muscle mass, age, or gender.

This can result in a BMI score with an inaccurate picture:

• Very muscular adults and athletes may be classed as “overweight” or “obese” despite their body fat being low.
• Adults who lose muscle as they get older may fall into the “healthy weight” range, yet they may be carrying excess fat, which can be dangerous.
• Pregnancy will affect a woman’s BMI result. Where the BMI will go up as weight increases. The pre-pregnancy weight should be used when calculating BMI.

Despite these limitations, the BMI is a straightforward and convenient way of assessing someone’s weight.