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.
Ways To Calculate Body Fat:
- Calipers. A measuring instrument that consists of two adjustable legs or jaws can be used to ‘pinch’ specific areas of the skin to determine how much fat sits beneath it.
- Air displacement plethysmography (ADP). This requires an individual to sit in a ‘BOD POD’. The BOD POD determines body composition (the ratio of fatty mass to lean mass). Body composition is divided into two body mass categories (fat mass & lean mass). The BOD POD test provides results of these two categories expressed as percentages of total body mass.
- Near-infrared interactance (NIR). Which is a specialised probe placed against an area of the body, emitting infrared light that passes through muscle and fat. The NIR machine then uses this information along with age and activity level to estimate body composition.
- Dual-energy X-ray absorptiometry (DXA). This uses a small dose of ionizing radiation to produce pictures of the inside of the body which can pick up areas of body fat.
- Bioelectrical impedance scales. These work with the help of sensors in the scales in which a small electrical current runs up through the leg and across the pelvis, measuring the amount of resistance from body fat. Then, the sensors in the scale measure the level of resistance that the current met as it travels back through the other leg. This is what I use with clients and they give a rough estimate of an individual’s body fat level.
If you want to track your body fat levels at home, the bioelectrical impedance scales I use with my clients can be bought here and I recommend you pair them with the FeelFit App to keep track of all aspects of your weight.
Although most of these methods of body fat measuring are still producing estimations, they certainly have a more conclusive calculation of overall health than the BMI method. Personally, I would like to see more GP surgeries and health practices making use of the modern ways available to us to establish if an individual’s weight is a health risk or not.
BMI calculations are not the best method of weight management. Any increase in weight is automatically attributed to fat but could just as easily be an increase in healthy lean muscle tissue if taking part in regular exercise or weight training. A healthy weight is hard to figure exactly as one size does not fit all and factors that affect healthy weight include:
- General health
- Bone density
- Body type
If weight management is something you are wanting to investigate for yourself, I would always recommend that you speak to a professional who is qualified in this area. When a client comes to me with this as their goal, I discuss their lifestyle, medical history, lifestyle habits as well as taking a thorough evaluation of their body statistics using the bioelectrical impedance scales. Only then can I establish what their current health is and how they can make improvements in the safest way possible.
We have come so far in biological science since the 1800s and there is more known about our bodies and how certain things influence our health. I am baffled as to why the BMI scale is still in use in the 21st century and I encourage everyone to look at the bigger picture when assessing their general health. A balanced lifestyle is achieved with limited processed foods, regular exercise, and eliminating unnecessary risks.
For more support with your physical wellness head to my online fitness membership and if you want to gain a balance in all aspects of your lifestyle, head to my Wellness Training to learn how to create better habits, improve your wellness and live a happier healthier life.