Have you ever wondered what Body Mass Index, or BMI, is all about?  Let’s explore what it is, why it is used and when it is not so reliable.

BMI is one of the tools that your health professionals use to assess your potential health risks. It compares your height and weight to see if you are a healthy weight for your height. It is calculated using your body weight in kilograms and height in meters. Here is what the score means:

18.5 and under – underweight

18.5 – 24.9 – healthy weight

25 – 29.9 – overweight

30 – 34.9 – obese

35 and above – severely obese

It can be a useful tool as carrying excess body fat increases your risk of health problems. These include risk of:

• insulin resistance
• type 2 diabetes
• heart disease
• fatty liver disease
• some cancers

Limitations

BMI has limitations. It is a health guide that was designed to assess Northern European Caucasian adults. It doesn’t take into account age, ethnicity, gender or body composition.

BMI is less accurate in:

• Body builders and weightlifters
• Some high performance athletes
• Pregnant women
• People over 65
• People with a physical disability
• People with Polynesian, Pacific Island, Aboriginal, South Asian, Chinese and Japanese heritage

Note that BMI calculation is not suitable for use in assessing children.

If your BMI is above target it may help you to have a chat with your health professional. They will look at other markers that can give more information about your health. These include waist measurement, fat distribution, fitness level, blood pressure, blood glucose and cholesterol levels.

Other ways to assess body fat

Waist measurement

Often people who are overweight have an excess amount of fat around their mid-section. This is known as visceral fat. This fat increases health risks as it coats the heart, kidneys, liver, digestive organs and pancreas.

Here is a waist measurement general guide:

Gender	Increased risk	Higher risk
Men	94 cm or more	102 cm or more
Women	80 cm or more	88 cm or more

This is a general guide only. Those from Maori, Pacific Islander heritage would be slightly higher measurements. People from Asian backgrounds need to be on the lower end to reduce their health risks.

Skin fold callipers

These measure excess fat under the skin, known as subcutaneous fat. The skill of the person performing the skinfolds can vary which could greatly impact the outcome and accuracy of the result.

DEXA Scan

If you and your healthcare professional want to explore your body composition in detail you can have a Dual-Energy X-ray Absorptiometry (DEXA) scan taken.  This involves you lying on your back for approximately 10 minutes while an X-ray scans over your entire body. It can give detailed body measurements of weight, fat placement, muscle mass and bone density. It is attended at a specialised clinic which can be expensive.

All these tools can be used to highlight a person’s need to make health changes. And remember that even small lifestyle changes can result in significant health benefits.

If you have any questions or concerns, see your doctor or call our helpline on 1300 342 238 and ask to speak with one of our health professionals.

Monica McDaniel-Wong, Credentialled Diabetes Educator