Body Mass Index (BMI) and waist circumference

More than 60% of Australian adults are overweight or obese and the figure is rising. Being overweight or obese can cause many serious health problems.

BMI and waist circumference can help assess overweight and obesity levels.

Two methods are commonly used to estimate whether you are a healthy weight or not are body mass index (BMI) and waist circumference.
Waist circumference is considered a good estimate of your body fat, especially your internal fat deposits and your likelihood of developing weight-related disease.
Health professionals often use BMI and waist circumference together to assess overweight and obesity and assessing risk of cardiovascular disease and diabetes.

What is Body Mass Index (BMI)?

Even small amounts of weight loss bring health benefits

BMI uses weight and height to determine if an adult is within the healthy weight range, underweight, overweight or obese.
It provides an estimate of total body fat and your risk of developing weight-related diseases.
BMI is calculated by dividing weight by the square of height as follows:

BMI = Weight (kg)/Height (m)2

Use the healthdirect BMI calculator to work out your BMI.
The calculator indicates any health risks in relation to your BMI or waist circumference, and offers information tailored to your personal results.
If you calculate your BMI yourself it is important to make sure you measure your weight in kilograms and your height in metres.
BMI ranges for weight classification in adults are below:

< 18.5 Underweight
18.5–24.9 Healthy weight range
25.0–29.9 Overweight
30.0–34.9 Obesity I
35.0–39.9 Obesity II
≥ 40.0 Obesity III

Limitations of BMI

BMI is less accurate for assessing healthy weight in some groups of people, as it does not distinguish between the proportion of weight due to fat or muscle. BMI is therefore less accurate in certain groups, including:

• certain ethnic groups such as Pacific Islander populations (including Torres Strait Islander peoples and Maori), Aboriginal peoples, South Asian, Chinese and Japanese population groups
• body builders or weight lifters
• some high performance athletes
• pregnant women
• the elderly
• people with a physical disability
• people with eating disorders
• people under 18 years
• and those with extreme obesity.

Why measure waist circumference?

Waist circumference is a better estimate of visceral fat, the dangerous internal fat which coats the organs. It is therefore a more accurate predictor of cardiovascular risk, type 2 diabetes in women and metabolic syndrome.

How do I measure my waist circumference?

To find out your level of risk, it is important to measure your waist circumference accurately.

1. Place the tape measure directly on your skin, or over no more than one layer of light clothing.
2. The correct place to measure your waist is halfway between your lowest rib and the top of your hipbone. This is roughly in line with your belly button.
3. Breathe out normally and measure.
4. Make sure the tape is snug, without squeezing the skin.

Waist circumference and disease risk

Waist circumference thresholds which indicate increased risk of disease are below:

For women:

• risk is increased at ≥ 80 cm
• risk is high at ≥ 88 cm

For men:

• risk is increased at ≥ 94 cm
• risk is high at ≥ 102 cm for men

Limitations of waist circumference

Waist circumference is less accurate in some situations, including pregnancy, medical conditions where there is distension of the abdomen, for certain ethnic groups and for children and young people.

What is overweight and obesity?

Overweight and obesity are conditions of excess weight that normally result from either excess energy intake (food) and/or insufficient physical activity. Certain medications and medical conditions can also cause weight gain.
Overweight means having a BMI of 25 or over, while obesity means having a BMI of 30 or over.

What are the health risks of being overweight or obese?

Being overweight or obese can directly contribute to developing many serious health problems, including:

• type 2 diabetes
• high blood pressure
• cardiovascular disease
• sleep apnoea
• and osteoarthritis.

Many of these diseases can be prevented by maintaining a healthy weight and following a healthy lifestyle, including a well-balanced diet and regular physical activity.

It is encouraging to know that even small amounts of weight loss bring health benefits, including lowered your risk of heart disease and type 2 diabetes.

How can I lose weight?

A multi-pronged lifestyle approach that combines improved nutrition, increased physical activity and psychological support is likely to be most successful in promoting weight loss.

For many people achieving a ‘healthy’ weight is an unrealistic expectation. A weight loss of 5% is more achievable and will still result in important health improvements. Your goals should focus on behaviour change and improved health, rather than weight loss.

More intensive approaches, such as very low-energy diets, weight loss medication and bariatric surgery may be needed in some people, especially those who are obese, have other risk factors, or have been unsuccessful in reducing weight using lifestyle approaches alone.

How can I reduce my risk of weight-related disease?

While waist circumference and BMI are important indicators of disease risk, many other factors also contribute.

There are many ways to improve your health, including:

• quitting smoking
• increasing physical activity
• improving diet
• reducing alcohol intake
• treating other risk factors such as high blood pressure and high cholesterol
• and getting enough sleep.

Remember, increased physical activity and improved diet will help reduce disease risk and have a health benefit independent of weight loss.

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Sources: http://www.healthdirect.gov.au
Measure Up (How to measure yourself, Weight and waist measurment), National Health and Medical Research Council (Clinical practice guidelines for the management of overweight and obesity in adults, adolescents and children in Australia - PDF Document)