Do you know your BMI? All of us have probably encountered the Body Mass Index, whether at the doctors, at the gym, or online.
Body Mass Index (BMI) is used internationally, both by healthcare professionals and individuals, to determine whether they are underweight, normal weight, overweight, or obese.
The formula to calculate it is simple:
BMI = weight(kilograms) / height²(meters)
However, BMI has been criticised for being an inaccurate measure of body composition and overall health.
Limitations of the BMI calculation
One of the main criticisms of BMI is that it doesn’t take into account the difference between muscle mass and fat mass.
A person with a high muscle mass, such as an athlete or bodybuilder, may have a high BMI but still be considered to be in good health.
On the other hand, a person with a low muscle mass and a high amount of body fat may have a normal BMI but still be considered to be at risk for health problems.
Another issue with BMI is that it doesn’t take into account where fat is stored on the body.
Visceral fat, which is stored in the abdominal area, is a greater health risk than subcutaneous fat, which is stored just under the skin.
However, BMI does not distinguish between these two types of fat.
So then, why does BMI matter?
In general, doctors determine that the higher your BMI, the higher the risk of developing a range of conditions linked with excess weight, including;
- liver disease
- several types of cancer (such as breast, colon, and prostate cancer)
- high blood pressure (hypertension)
- high cholesterol
- sleep apnea.
The BMI is therefore useful as a reference index, but its calculation remains approximate to determine health risks.
If BMI is so innacurate, what should we be measuring instead?
Instead of focusing on BMI, many experts including myself, recommend measuring body fat percentage as a more accurate indicator of overall health.
Body fat percentage is the amount of fat in the body as a percentage of total body weight.
A healthy body fat percentage for men is typically between 8-19% and for women is between 21-33%.
How to measure body fat percentage
Unfortunately, calculating your body fat percentage isn’t as simple as the BMI calculation and you can’t get an accurate measure just from plugging a few numbers into an online calculator.
The simplest (and cheapest) way to measure body fat uses the skinfold measurement. To do it a caliper is used to pinch body fat and measure it’s thickness on multiple sites of the body. You need to have experience and skill to perform the test correctly.
Other methods include bioelectrical impedance analysis, and dual-energy x-ray absorptiometry (DXA) which are a lot more high tech and harder to get hold of.
While none of these methods are not foolproof, they are generally considered to be more accurate than BMI.
It is important to note that body fat percentage is not the only indicator of health. Other factors such as diet, exercise, and overall physical activity should also be taken into account.
However, measuring body fat percentage can give a more accurate picture of an individual’s body composition and overall health.
The bottom line
While BMI is a widely used measurement to determine weight status, it is not a accurate indicator of overall health. But it’s still a useful starting point for important conditions that become more likely when a person is overweight or obese.
In my view, it’s a good idea to know your BMI. But it’s also important to recognise its limitations.
With the clients I train in Henley-on-Thames and online, we focus on body fat percentage (using the skinfold test) alongside alongside other factors such as diet, exercise, overall physical activity to portray a much more accurate picture of overall health, wellness, and happiness.
If you are worried about your health and want to learn some life-long tools for managing your weight, get in touch to talk about my VIP coaching.