Body Mass Index (BMI) & Waist-to-Height Ratio

Here is an introduction to a couple of different calculations we use to monitor your overall well being here at Try Fitness. They are useful to get an understanding of so you can gain a deeper insight into your health as well as allowing you to see the physical results of your hard work.

Body Mass Index

Your BMI is a measure of the ratio of body fat to total body weight. It is used to determine whether a person is underweight, healthy weight, overweight or obese and it is calculated by dividing your weight in kilograms by your height in meters squared. A person who is 1.7m tall weighing 65kg has a BMI of 22.5 which would put them perfectly in the “healthy” zone as you can see using the table below.

A BMI in the healthy weight range is associated with the lowest risk of disease, there are risks associated with being at either extreme end of the scale. Being underweight can bring malnourishment, deficiency in essential vitamins, and anemia to name a few, and obesity is responsible for things such as high blood pressure, heart disease, and diabetes.

These ranges don’t discriminate, they apply to all ethnic groups in line with the World Health Organisation’s recommendation not to use specific ethnic BMI ranges. It is important to remember that although highly valid, these calculations are only a guide and should only be used on people over the age of 18. The calculations will also not work on those who are very muscular, pregnant, or those who are extremely tall or short (more than 1.9m or less than 1.5m).

Waist-to-Hip Ratio

The waist-to-hip ratio is a quick measure of fat distribution that may help indicate a person’s overall health. It is calculated by taking the circumference of the waist and dividing it by the circumference of the hips. Feel like you are back in maths class? Don’t worry, you just need to take the measurements, our progress tracker does the calculations and that allows us to focus on more important stuff like, what a person’s waist-to-hip ratio can tell us about their health.

The reality is that people who carry more weight around their middle, rather than their hips, may be at a higher risk of developing certain health conditions such as cardiovascular disease or diabetes. According to the World Health Organisation, having a WHR of over 1.0 may increase the risk of developing one of these conditions commonly linked with being overweight. So, a person whose waist circumference is 80cm with a hip circumference of 90cm would have a WHR of 0.89cm. The WHO advise that healthy WHR is:

0.85 or less for women

0.9 or less for men

So assuming the person in our example above is a man, they are sitting perfectly in the safe zone. The chart below illustrates how the WHO classifies the risk of being affected by weight-related health conditions according to the WHR:

While WHR is a useful tool and a quick way to get an indication of a person’s overall health, obesity levels and their risk of weight-related health conditions, human error on the measurement or calculation is always a possibility and so it should never be relied upon as the sole measure of obesity or health risks. If you suspect you may have any underlying issues, speaking to a Doctor is always the best way to get a more complete picture.WHR is not designed to be used on anyone under the age of 18.