• BMI doesn't distinguish between body fat and muscle mass. Muscle weighs about 18 percent more than the same amount of fat. So, according to BMI, the muscled person is more overweight than a sedentary person.
• BMI is also not reliable to use on elderly adults, who continue to lose muscle and bone mass with age. An overweight older adult may appear to be within a normal BMI range.
• The BMI calculation is based on Caucasian body types and may not be appropriate for people of other ethnicities.

A person whose BMI indicates they are overweight or obese is generally considered unhealthy. But 2016 research suggested that this was incorrect for 75 million Americans.

• Researchers found that 54 million Americans that were classed as overweight or obese were perfectly healthy when th...