You may be aware of Body Mass Index (BMI), but you might not know exactly how it works or how it is calculated. BMI divides a person’s weight by their height to the power of 2, or square:

BMI = weight (kg) / height²
According to most criteria accepted around the world:

• A BMI of 18.49 or below means a person is underweight
• A BMI of 18.5 to 24.99 means they are of normal weight
• A BMI of 25 to 29.99 means they are overweight
• A BMI of 30 or more means they are obese

Where did this calculation come from?

Adolphe Quetelet, a Belgian astronomer, mathematician, statistician, and sociologist, devised the basis of the BMI between 1830 and 1850 as he developed what he called “social physics”. The modern term “body mass index” (BMI) was coined in a paper published in the July 1972 edition of the Journal of Chronic Diseases by Ancel Keys and others.

Just take a moment to think about all that.

This form of measuring the ‘health’ of individuals was created over 170 years ago! If this formula seems complicated and somewhat illogical for modern life, that is because it is, with many experts starting to question BMI accuracy.

In 2013, Prof. Nick Trefethen, a mathematician from Oxford University wrote a letter to The Economist, in which he questioned the usefulness of the current BMI formula, calling it a “bizarre measure.” He argued that the formula leads to confusion and misinformation. The height term, he says, divides the weight by too much when people are short, and by too little when they are tall. The BMI calculation does not measure overall lean muscle or overall fat content.

The result is that short people being told they are thinner than they really are, while tall people are made to think that they are fatter than they are. Trefethen points out that any calculation that assigns one number to a person will not be perfect. Humans are too complex to be described by a single figure, we are three-dimensional beings.

We live in a different world than in the 1800s, have different technology and science available to us. More science has emerged that reveals the flaws of this approach, yet it is still the go-to method of health professionals to deciphering if we are putting our health at risk.

Here is an example of where the issues occur. We can have two different people;

• A person who does not exercise is 1.83 meters, or 6 feet tall and weighs 92 kg, or 203 pounds (lbs), would have a BMI of 27
• An Olympic athlete, 1.83 meters, or 6 feet tall, and weighs 96 kilograms, or 211 lbs, would have a BMI of 28

But, which of the two is likely to be the healthiest?

You would put your money on the Olympic athlete, and it will be a safe bet because muscle weighs about 18 percent more than fat which is why their overall weight is more than that of the person who does not exercise. Also, as we age we tend to lose muscle mass which could grade someone within healthy BMI ranges, when they may have excess fat, particularly visceral fat. This type of fat wraps around your abdominal organs deep inside your body and cannot feel or see it. In fact, it is possible to have a flat tummy and still have higher levels of visceral fat.

Too much body fat is bad for our health. But compared to the fat that lies just underneath the skin (subcutaneous fat), the visceral kind is more likely to raise the risk for serious medical issues. Heart disease, Alzheimer’s, type 2 diabetes, stroke, and high cholesterol are some of the conditions that are strongly linked to too much fat in the body.

As a professional in the health and fitness industry, I use body fat levels as a more accurate indication for understanding the health of an individual. Studies have suggested that measuring fat gives a more accurate view of health and health risks, but getting an accurate measure is not easy.