Virtual Medical Centre

BMI (Body Mass Index)

• Introduction to the body mass index (BMI)
• What does your BMI mean?
• Why are BMIs useful?
• Risks associated with extreme BMIs
  • Overweight
  • Underweight

Introduction to the body mass index (BMI)

The body mass index (BMI) is a physical measurement used to assess an individual's total amount of body fat. The BMI was invented by Belgian polymath Adolphe Quetelet in the 1800s, and consequently is sometimes known as the Quetelet index. The BMI is calculated by dividing your weight in kilograms (kg) by your height in metres squared (m²). It is expressed as kg/m². Calculate your BMI using the calculator below, then compare your result to the BMIs in Table 1.

What does your BMI mean?

The BMI scores give an indirect measure of body fat. Depending on the BMI value calculated you may be underweight, normal weight, overweight or obese. The cut off values are as follows:

Table 1: BMI cut-off values

Why are BMIs useful?

The BMI is a simple, inexpensive screening tool used to identify possible weight problems for both adults and children. A BMI measurement is useful to assess who needs further testing to identify health risks such as heart disease. Individuals at risk will need further assessment. Assessments may include skin fold thickness test, diet, physical activity level, family history and other appropriate health screenings.

Risks associated with extreme BMIs

Being either overweight (with a BMI of 25 or above) or underweight (with a BMI lower than 18.5) can affect your health.

Overweight

Being overweight increases your chances of developing disease. An overweight individual whose BMI rises from 25 to 27 is 20–30% more at risk of death. As an individuals BMI rises above 27, the risk of death increases more steeply by almost 60%. If you are overweight and have low physical activity, the risks of developing disease increase.

Diseases associated with being overweight include:

• Gastrointestinal disorders;
• Cardiovascular diseases (i.e. stroke, heart attack);
• Diabetes;
• High blood pressure (hypertension);
• Osteoarthritis;
• Infertility;
• Some forms of cancer (i.e. breast, colon and endometrial cancers);
• Menstrual abnormalities;
• Gall bladder disease;
• Sleep problems (e.g. obstructive sleep apnoea);
• Respiratory problems (i.e. asthma).

Risks of being underweight

If you are underweight you may be malnourished and in addition you may develop the following nutritional deficiencies:

• Compromised immune function with increased susceptibility to infections;
• Respiratory diseases;
• Digestive diseases;
• Cancer;
• Osteoporosis;
• Increased risk of falls and fractures.