Is BMI a Useful Measure of Health

Body Mass Index (BMI) is a value derived from the mass and height of a person. It is defined as the body mass divided by the square of the body height, and is expressed in units of kg/m², resulting from mass in kilograms and height in metres.

BMI is essentially used to work out whether your weight is healthy or not. It works by taking an adult’s weight in KG and dividing it by their height squared. For example, if you weigh 70kg and are 1.70m tall you work it out by:

1.70 x 1.70 = 2.89

70kg divided by 2.89 = 24.2

When you have found your BMI number you can compare it to normative data to see if you’re at a healthy weight.

Whilst this is a method that has been used for decades, is it really the best approach to measuring our health?

The Limitations of BMI

The main argument against using BMI as a good health indicator is that it is an impracticable measure for a lot of sports people.

BMI doesn’t factor in muscle mass, so if an individual that regularly competes in sport or physical activity measures there BMI, they are likely to get a reading that is incorrect as their muscle mass percentage will typically be higher than the general population. A good example of this would be a rugby player. An individual with a heavy weight, medium height and high percentage of muscle mass is expected to have a BMI number higher than recommended, and therefore deemed to be unhealthy. This would be very far from the truth.

BMI is a much useful measurement for the general population, but not ideal if you enjoy endurance sport and muscle building as you are likely to get a BMI reading that misrepresents your true health.

BMI calculations also do not account for the distribution of fat in the human body. For example, if a person has a high concentration of fat surrounding their mid-section, this could increase the chances of them contracting diseases such as diabetes. However, if the fat is evenly distributed around the body, the health risks may not be as severe. This is a real limitation when using BMI as individuals that are seeking help for weight loss as you do not get an indicator of areas to target.

Other Practical Ways to Measure Health

Waist circumference is a great measure of fat around your abdomen. A larger waist usually indicates that you have excess fat inside your organs. This is also linked to having a high blood pressure, diabetes and high blood fat levels. To measure your waist, you can use a tape measure or the “string test” you can do this by cutting a piece of string as long as your height, halve the string and see it the two ends meet when wrapping it around your mid-section. If the two ends meet, you’re a healthy weight. If they don’t, you may need to change some of your lifestyle habits.

High cholesterol is a result of having too much fatty substance in your blood. Most of the time it is caused by having a poor diet, drinking too much alcohol and even smoking. A blood test would show your levels of HDL (high-density lipoprotein -good cholesterol) and levels of LDL (low-density lipoprotein-bad cholesterol). Having your levels tested can be a great indicator as opposed to BMI in finding out how healthy you are and what you are made up of, as the test will show you what your blood contains.

If you would like more information on your own body composition, please don’t hesitate to contact a member of the Cottonmill fitness team.