What is body mass index (BMI)?

So, what is your body mass index (BMI), and why should care what your BMI is?

Your body mass index (BMI) is calculated by dividing your weight in kilograms, by your height in meters squared.

Therefore, if you weigh 85 kg, and are 1.8 meters tall:

If the value is below 20 then you are considered underweight, a value between 20 and 25 is ideal, above 25 is viewed as overweight, and above 30 as obese.

So, why care? Well, there is evidence that if a BMI is below 20, or above 30, then there is an increased mortality rate, and an increased chance of developing conditions such as heart disease and diabetes. However, it should be noted that there is also some evidence that contradicts these findings. The matter is unclear as it depends on how the various studies were performed and whether or not other risk factors besides BMI were considered, or adequately controlled. (For a review of these matters see Lewis et al., 1990).

Therefore, as there is evidence that your BMI may be an indicator of ‘health’, and your chances of developing certain conditions, then you should know what your BMI is, and if it is high, or low, take steps to change it.

It should be noted though that BMI values are ‘meaningful’ for children, the elderly or professional athletes.

If you wish to work out your BMI then cal.culate.it offers a range of BMI calculators and these can bee seen on our ‘health and fitness’ page. The calculators work in kilograms, pounds, stone and pounds for weight, and feet and inches, or meters, for height.

References

Cora E. Lewis, Kathleen M. McTigue, Lora E. Burke, Paul Poirier, Robert H. Eckel, Barbara V. Howard, David B. Allison, Shiriki Kumanyika, and F. Xavier Pi-Sunyer – AHA Science Advisory: Mortality, Health Outcomes, and Body Mass Index in the Overweight Range. A Science Advisory From the American Heart Association, Circulation. 2009;119:3263-3271 [web link]