Body Mass Index (BMI) and health

A risk factor for many diseases - including cardiovascular disease, fatty liver disease, and diabetes - is weight. The BMI is calculated using a person's weight and their height. Your BMI is an indication of whether your body mass is at a healthy level in proportion to your height. A very high BMI means that someone is overweight or even obese.

There are different charts for adults and young people. The BMI which has been calculated is compared to the appropriate chart in order to discover whether the person is underweight, a healthy weight, overweight or obese.

curriculum-key-fact
Body mass index (BMI) =  \frac{body~mass~in~kilograms} {(height~in~metres)^2}
Question

A 16 year old boy has a body mass of 65 kg and is 1.70 m tall. Calculate his BMI.

Use the equation body mass index (BMI) =  \frac{body~mass~in~kilograms} {(height~in~metres)^2}

BMI =  \frac{65} {1.70 \times 1.70}

=  \frac{65~kg} {2.89~m^2}

= 22.5 kg/m2

Using a BMI chart for boys aged 2-20, a BMI of 22.5 kg/m2 is in the 'healthy' range.

BMI and disease

People with a very high body mass index (BMI) are defined as obese.

Obesity leads to high blood pressure and the build-up of fatty deposits in the arteries, which lead to cardiovascular disease. It also increases the likelihood of developing diabetes, another risk factor for cardiovascular disease.

Being obese - with deposits of lipids in the abdomen - increases blood pressure beyond normal levels and increases levels of blood lipids.

Type 2 diabetes

Body fat also affects the body's ability to use insulin.

Type 2 diabetes is where the body's cells lose their sensitivity to insulin - they no longer respond, or respond less effectively, to the insulin that's produced. This causes glucose levels in the blood to rise to dangerous levels.

Obesity accounts for 80 to 85 per cent of the risk of Type 2 diabetes. Rising obesity is linked with 'western diet' - a diet that includes energy-rich 'fast foods' and an inactive lifestyle. The bar charts show the increased risk of developing Type 2 diabetes associated with people's body mass index (BMI).

The bar charts show the increased risk of developing Type 2 diabetes associated with people’s Body Mass Index.

There is no cure for Type 2 diabetes, but it may be possible to control it by diet and exercise. The risk of developing cardiovascular disease and Type 2 diabetes can be reduced by eating a balanced diet, with unrefined, unprocessed, 'whole foods', and taking regular exercise.