Is the BMI still relevant?

August 2, 2012, 5:24 pmYahoo!7

Recent research suggests the body mass index (BMI) is losing prominence as "the" tool for measuring health. So we asked our experts: is BMI a useful way to assess health risks?

Life & Features


Dr Robert Grenfell national clinical issues director at the Heart Foundation

No measurement is perfect in all circumstances, but for most people, BMI is a useful guide to whether you’re at a healthy weight or not.

When it comes to predicting risk of chronic diseases like heart disease, waist circumference is often seen as a better tool because carrying weight around your middle can be dangerous.

Overall, however, the differences between BMI and other indicators like waist circumference, waist-to-hip and height-to-waist ratios are rarely clinically significant. Studies show the variation is subtle and would be unlikely to make a significant difference for the individual person. BMI is a useful measurement for most people over 18, but there are limitations to be aware of as it may be influenced by age, gender and ethnicity.

If you’re pregnant, BMI doesn’t apply and you should consult your doctor on where a healthy weight sits. People who are likely to be unhappy with their BMI are athletes because their results may show as overweight – muscle weighs more than fat and BMI doesn’t take this into account. If people are unhappy with their BMI, they can complete a waist circumference assessment.

Nearly 10 million adult Australians are now overweight or obese (based on BMI calculations) and for most of those people, that’s an accurate reflection of their weight range. That means nearly 10 million adult Australians are facing a higher risk of heart disease, diabetes, some cancers and numerous other health problems.

Tackling our expanding weight problem needs to be our top priority. What’s important is that people get their measurements taken and act on the result, rather than focus too much on the measurement method.


Dr Richard Telford, associate professor at the Australian National University Medical School ACT

Average BMI gives us a very rough idea of whether our population in general is getting fatter or not, but it is rough. The problem is that it can’t distinguish between fat, muscle or bone.

As Australians have become bigger over recent decades, we have increased our lean tissue as well as fat, so BMI tends to overestimate increases in our population’s fatness. But where BMI can get it completely wrong is in estimating individual fatness. I remember measuring a champion rugby league player who was 105kg and 1.83m, which made his BMI 31.4 and classified him as obese. This was absolute nonsense as the chap was a ball of muscle, but BMI didn’t know that.

And take the case of 35-year-old Kate. At 70kg and 1.5m, her BMI was 31.1 and we measured her body fat accurately by scan at 33.1 per cent. Kate wisely decided to consult a fitness advisor and a dietitian. After six weeks of conscientious work, she was demoralised to find that her BMI and weight had not budged. However, her follow-up scan showed her fat percentage had actually dropped to 31.5 per cent. Kate had shed one full kilo of fat, but had increased her muscle mass by one kilo as well. She was relieved to find she was slimmer, more toned, and healthier without her BMI changing.

But there is another even more important fact to consider. Studies have consistently shown that it is not unusual for an overweight, but physically active person to be healthier than a normal or underweight person who is inactive.

The message I like to send to all people with high BMI is to get up and move around regularly throughout the day. Physical activity is great (in fact, vital) for your health, irrespective of any weight loss.

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  1. Lyn elizabeth09:24am Monday 04th February 2013 ESTReport Abuse

    This is just so silly. Obviously is someone is just a little chubby or a little skinny it's not going to do them any harm it's the extreme weights under or over that are harmful. Even then it depends on how you live. I'm considered morbidly obese on this scale ie over 45% but work a physical job and play sport 3 times a week and yes at a competitive level for those who think I'm too fat. I'm far from lazy and consider myself pretty healthy. BP normal colesterol low and I'm 49. I'm aware I need to lose alot of weight but that will happen when I'm ready. Anyhow just wanted to say to other 'fatties' keep active play sport and you could be healthier than the average weight couch potatoes!!

  2. Duncan02:48pm Tuesday 22nd January 2013 ESTReport Abuse

    BMI = a Joke. I am 5ft 6in all, Weigh 72kgs and just completed a half-ironman triathlon in under 5 hours. My body fate percentage is very low and my level of fitness exceptional. But this measure says I'm in the Danger zone. BS. And waist to height is a mess too. My waist is 27in - so I am also in the 'danger zone' for this measurement, but on the 'too small' side. No ratio works for all. The only thing that works is a detailed analysis of body fat, skeletal mass and muscle mass.

  3. maryanne01:45pm Tuesday 22nd January 2013 ESTReport Abuse

    BMI is right most of the time. O.K. it has its floors if you are an athlete, body builder, pregnant then BMI has its limitations. Guess what if you BMI is over 30 and you are not it the above categories then there is a 99% chance you are fat and its time to do something about it. I have heard all the excuses before, I have heavy bones, muscle weighs more than fat, these are just excuses that fat (sorry overweigh) people use to justify not getting of their backsides and doing some exercise. My suggestion if you BMI is over 30 see a doctor to get a proper assement and find out that you are overwieght.

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  4. Helen01:28pm Tuesday 22nd January 2013 ESTReport Abuse

    Exactly! Doctors also need to be well-educated on the basic fat % test (the good-old calipers) and use the hip:waist ratio for clearly/obvious obese people!

  5. Helen01:14pm Tuesday 22nd January 2013 ESTReport Abuse

    I cannot believe these "Experts" are just realising this NOW! Even when I was young and just starting out as a personal trainer (17!), even I completely disagreed with this form of "measurement" as muscle weighs 3 x more than fat! Completely useless on all accounts in my opinion!

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