The Body Mass Index — A Health Indicator Whose Time Has Passed

The BMI method fails to take a number of factors into account

The healthcare industry has always been interested in finding ways to measure the factors that contribute to optimum health. Among these measures is the body mass index, or BMI, a formula used to determine the “ideal” weight for good health.

The BMI is still used today, but critics contend that its initial premises are inaccurate, and that it can’t provide an accurate determination of whether someone is obese or whether their body proportions can lead to disease.

Here’s a closer look at the “body mass index,” where it comes from, and why some health professionals feel it falls short as an aid to predicting risks to health.

The History of the BMI Scale

The formula physicians use today as the body mass index was developed by Lambert Adolfe Quetelet, a Belgian mathematician, statistician, astronomer, and sociologist.

Quetelet was interested in a wide range of scientific subjects, but his interest in mathematics and statistics drove him to find a method to determine the proportions of an “average man.” His formula, developed in the 1830s, calculated the relationship between height and ideal weight, which is still used today.

In the 1970s, American physiologist Ancel Keys, advocated for using the BMI as the preferred method of determining normal, underweight, and overweight conditions that might affect human health. Keys was also instrumental in doing research on the relationship between diet, high cholesterol, and cardiovascular disease.

What Is the BMI Formula?

The BMI uses the metric system to calculate the height of the individual in meters, which is squared and then divided by the body weight in kilograms. Underweight is considered less than 18.5 kg/m. Normal weight would be a BMI from 18.5 kg/m to 24.9 kg/m. Overweight, 25 to 29.9 kg/m. A BMI over 30 would be considered obese. BMIs under 20 and over 25 are associated with higher mortality from all causes, with health risk appearing to increase the further the BMI number varies from the 20 to 25 range. These figures can be converted to other measurements and put into chart form for easy reference.

Where the BMI Measurement Falls Short

Since its introduction, a number of flaws in the BMI method have been noted. The initial data used mainly Western European men as subjects, skewing the results in certain ways. Women may have higher body fat, particularly in the lower body, which is normal and doesn’t indicate health risk. Similarly, short individuals will have a higher BMI, yet not have high levels of body fat, and may not be obese.

Also, the formula fails to consider differences between the weights of bone, muscle, and fat. Bone weighs more than fat, so individuals with high bone density may have a high BMI number but may not be fatter and may not have a higher risk for health problems. Those individuals who are highly muscled may calculate to a high BMI number but don’t have excess fat.

Not all demographic groups are built like Western European men and don’t fit the profile that produces the right BMI results. In addition, older individuals appear to benefit from a higher BMI, because some additional fat can protect against falls and other problems that increase risk.

Better Ways to Determine Health Risk

Because BMI fails to take into account a number of additional factors that can affect health and predict outcomes, health professionals use the calculation as only one method of determining health risk. Other methods, such as family history, diet patterns, exercise habits, and, particularly, waist circumference, can be more indicative of increased health risks in the future.