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The new BMI: Can a piece of string determine your obesity risk?

Dr Sandro Demaio

4 minute read
Dr Sandro DemaioCredit: Cath Muscat

Ever wondered the answer to the question, “How long is a piece of string?”. Well, it turns out our waist could hold the answer.

It seems every week there is a new health tip, trick or fad diet to try out. In this age of social media and 24-hour news, it can be confusing to understand what health recommendations are truly effective.

One question I get asked a lot is, “Am I a healthy weight?”

In general, the more body fat we carry, the greater our risk of a host of chronic diseases including type 2 diabetes, heart disease and even certain cancers. There are a number of reasons for maintaining a healthy weight, with weight gain also being a leading risk factor for chronic back and joint pain.

But with no two bodies created equal, how can we know if our weight is healthy or not?

Not all mass is equal

Body mass index (BMI) has long been considered a helpful recommendation for self-assessing our weight. BMI involves weighing yourself (in kilograms) and dividing the result by our height (in metres squared).

BMI was developed based on a European male population and is a helpful tool when reviewing the health of large groups of people. The result can then determine if they generally fall into the healthy weight range (18.5-24.9) or if they are considered overweight (25.0-29.9) or obese (over 30).

BMI, however, is not as great for determining or tracking the healthiness of an individual. The test has its flaws as the weight measured on our scales neither reflects whether that extra kilogram is muscle or fat, nor where the fat might be stored on our body – both of which are critical to our resulting risk of those same disease outcomes.

A 6ft-tall athlete, for example, may have the same BMI as someone of the same height and weight, who doesn’t exercise at all and has more fat than muscle.

A woman exercising in a park

What is visceral fat?

Visceral fat is the fat found on our waistline, wrapped around our vital abdominal organs – including the kidneys, liver, digestive organs and pancreas. When weight gain in this part of our body goes beyond healthy, it is known as central adiposity or central obesity. This type of weight gain can increase our risk of stroke, type 2 diabetes, heart disease and colorectal cancer.

How is visceral fat monitored?

While visceral fat is a useful predictor of chronic conditions, it can be hidden at low but still dangerous levels. This is due to the size of our abdominal cavity, but also because most of us don’t usually notice small increases in our weight.

Measuring our waist is a better indicator of a healthy weight as it takes visceral (abdominal or belly) fat into account. According to the Heart Foundation, for most adults, a waist measurement of greater than 94cm for men and 80cm for women indicates a higher-than-healthy level of internal fat. This measurement is more accurate, whatever our height or build, and these guidelines are based on the World Health Organization and National Health and Medical Research Council recommendations.

How do you perform the string test?

  1. Find the top of your hip bone and bottom of your ribs
  2. Breathe out normally
  3. Place the tape measure midway between these points and wrap it around your waist
  4. Then check your measurement – how long is the piece of string?

Please note: waist measurements should only be used for adults to check their risk of developing chronic disease

Who do the string test measurements apply to?

Like all tests of this kind, there are certain limitations to the insights they provide. According to the Heart Foundation, waist measurement is less accurate for certain groups such as Aboriginal and Torres Strait Islander peoples as well as South Asian, Chinese and Japanese adults. It is also less accurate for pregnant women and those with a medical condition where there is a distension of the abdomen. Talk to your doctor for more information.

So, take the test and assess your health! How do you measure up?

Co-host of the ABC TV series ‘Ask the Doctor’, author of 30 scientific papers and ‘The Doctor’s Diet’ (a cookbook based on science), Dr Sandro Demaio is an Aussie medical doctor and global expert on non-communicable diseases.

At nib, we want you to be at your healthiest. So, if Sandro’s tips have inspired you to get in shape, you might be eligible for one of our Health Management Programs at no additional cost for eligible members.*

Our Healthy Weight for Life program includes over $800 worth of meal replacement products, personalised service and online support. Find out more by visiting our Health Management Programs page.

*Available to eligible nib members who’ve held Hospital Cover for 12 months and served their relevant waiting periods. Additional criteria vary according to each program.

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