The Shape of the Problem
- Ciara Litchfield
- Aug 13, 2015
- 3 min read
BMI is something that many of us are aware of. It’s defined by the World Health Organisation as ‘a simple index of weight-for-height that is commonly used to classify underweight, overweight and obesity in adults. It is defined as the weight in kilograms divided by the square of the height in metres (kg/m2)’. BMI works best if you fall within the ‘average’ population, that is you are of average height and build. If you fall outside of the average parameters your BMI is unlikely to put you into the correct category. A tall slim female with a healthy diet is likely to be classed as underweight while I short muscular male may be categorised as obese.
A good example of this problem would be to compare Arnold Schwarzenegger to Danny de Vito.
Arnold is 1.88 m tall and weighs 120kg giving him a BMI of 34
Danny is 1.54 m tall and weighs 85kg giving him a BMI of 35
This puts them both in the obese category but with a very similar BMI.
So what would be a better way of calculating the risk our weight is having to our health?
For a long time there has been an association between health risk and, in particular, central obesity. This is storing fat around our middles. Assessing central body fat gives us a broader understanding and better chance of early diagnosis for many related diseases.
Ashwell proposed comparing height to waist circumference instead weight. This calculation is still very easy to conduct, you taking a waist measurement (cm) (take the tape in a horizontal line 1 inch above your belly button.) and dividing it by height (cm).
Let’s go back to Arnold and Danny
Arnold has a waist measurement of 90cm so would have a waist to height ratio (WHtR) of 0.47 (90/188)
Danny has a waist measurement of 110cm so would have a waist to height ratio (WHtR) of 0.71 (110/154)
This gives us a much better idea of whos’s health is at risk when it comes to central obesity.
Ashwell found that the correlation between a high WHtR and mortality in both genders was much clearer than the correlation found using BMI.
Like BMI WHtR has cut off points:
MEN
Ratio less than 35: Abnormally Slim to Underweight
Ratio 35 to 43: Extremely slim
Ratio 43 to 46: Slender and Healthy
Ratio 46 and 53: Healthy, Normal Weight
Ratio 53 to 58: Overweight
Ratio 58 to 63: Extremely Overweight/Obese
Ratio over 63: Highly Obese
WOMEN
Ratio less than 35: Abnormally Slim to Underweight
Ratio 35 - 42: Extremely Slim
Ratio 42 to 46: Slender and Healthy
Ratio 46 to 49: Healthy, Normal Weight
Ratio 49 to 54: Overweight
Ratio 54 to 58: Seriously Overweight
Ratio over 58: Highly Obese
Ashwell published the associations between measurements and Years of Life Lost YLL:
Slight Increased YLL at WHtR <0.4 ‘Take Care’
Minimum YLL at WHtR 0.4 to 0.5 ‘OK’
Slightly Increased YLL at WHtR 0.5 to 0.6 ‘Consider action’
Much increased YLL at WHtR >0.6 ‘Take action’
It’s important to take responsibility of your own health and using these simple tools is s great way to keep a track of where you are and motivate you to improve. Everyone body is different but finding a healthy routine that suits you is important. And if you ever get stuck or need a personalised plan you know where I am ;)
