Many people believe that some weight gain is an inevitable part of ageing. This is often called the middle-aged spread. They ask themselves “am I fat? Or just a little pudgy? The truth is that weight gain and ageing are not necessarily connected.

Measuring obesity

Body Mass Index (BMI) is the ratio between an individual’s height and weight.

The problem with BMI as a measurement of obesity is that people come in all different shapes and sizes and as a result they carry their weight in different places.

Individuals with a lot of muscle (which weighs more than fat) have an artificially high BMI; this means that their BMI rating is classified as obese when they are actually a healthy weight. This is one reason why BMI is not always considered a good risk indicator for obesity. The best examples of this are England rugby players. They carry a lot of weight in their muscles so proportionally when they calculate BMI it suggests that they are obese. In actual fact these players are fit and healthy.

For this reason other methods of measuring a person’s risk of obesity are now more regularly used. A better indicator of obesity is waist circumference.

How to measure your waist

Waist circumference is a good measure of a person’s risk of obesity because the more dangerous type of fat, called central fat, is carried around a person’s abdomen.

It is very quick and simple to measure waist circumference and only requires the use of a tape measure. There is a strong correlation between waist circumference and the risk of a person carrying too much visceral fat, the fat that is in and around a person’s organs. This is the most dangerous type of fat as it can create problems with how well organs are able to function.

Using waist circumference to measure obesity in women:

• A measure of 80cm is classified as overweight (BMI 25)

• A measure of 88cm is classified as obese(BMI 30)

Using waist circumference to measure obesity in men:

• A measure of 90cm is classified as overweight (BMI 25)

• A measure of 102cm is classified as obese (BMI 30)

How is waist circumference measured?

It is important to measure waist circumference in a particular way to maintain consistency.

Many people believe waist circumference is the same as measuring where they wear their belt or use the waistline of their trousers as a measure. These measures are not a measure of waist circumference.

Waist circumference is measured halfway in between the hip bone and the lowest rib parallel to the floor. An individual takes a deep breath in and then exhales. The measurement is taken when they’ve fully exhaled.

It is not just important to measure obesity, but also for the person to act upon it by visiting a GP or nurse, or by looking at the other resources offered in this section.

Dr Matthew Capehorn, Obesity Specialist
Chairman of the Yorkshire and the Humber region of the National Obesity Forum

10044 November 2011