Healthy Measure: Replacing BMI with something else

That means a 6ft (72 inch) tall man should aim to keep his waist less than 36 inches, while a 5ft 4in (64 inch) woman should keep hers under 32 inches.

They have found that the easy-to-calculate ratio between the two is a better predictor of risk than the most widely measure of obesity, called body mass index (BMI).

The team, who analysed the health of some 300,000 people, found this ratio was a better predictor of high blood pressure, diabetes and cardiovascular events like heart attacks and strokes than body mass index.

While BMI is used almost universally in the medical profession, most people are unfamiliar with it, partially because it is not a straightforward calculation.

BMI is calculated by taking one’s mass in kilograms and dividing it by the square of one’s height in metres.

Dr Margaret Ashwell, former science director of the British Nutrition Foundation, and now an independent consultant, spearheaded the study. She is presenting the research at the European Congress on Obesity in Lyon, France, on Saturday.

“Keeping your waist circumference to less than half your height can help increase life expectancy for every person in the world,” she said.

The ratio was also better than just taking a waist measurement, she added, as it took into account differing height between individuals and ethnic groups.

While BMI was a useful indicator, it failed to take into account the distribution of fat throughout the body.

Abdominal fat, around the heart, liver and kidneys, has been found to be worse than that on the bottom and hips, in terms of heart disease and diabetes.

Dr Ashwell suggested the waist-to-height ratio should be considered as a screening tool.

Margaret Ashwell has been advocating a waist-to-height ratio (WHTR) of 0.5 or less since at least August 2005, thus roughly the last seven years [1]. Ashwell’s collaborator, Shiun Dong Hsieh, has been advocating the use of WHTR since at least 1995, thus the last seventeen years [2].

A slightly more demanding but also handy measure that is useful as a motivational tool, is that our waist should be less than or equal to our inside pants leg.  (For most folks, our inside pants leg is about two inches less than our actual inside leg, measured from the floor to the underside of our crotch.)

Hence, if we usually buy a pair of trousers with an inside leg of 30 inches, then the trousers’ waist should be the same – just 30″.  The advantage of the trousers’ method is that we don’t even need a tape measure, or have to worry about exactly where we place the tape, or how tight the tape should be etc.  If we can’t fit comfortably into a pair of trousers that has a waist the same as the correct inside leg for us, then we’re still too fat.

Further, the trousers’ method can give us a hard but realistic goal to aim for because we can buy the right sized trousers in the hope that one day we will be able to fit into them comfortably.  In the meantime, we can feel how tight they are, or how much of a gap there is when we have to leave the top undone.  For some folks, the motivational effect of this may be more concrete than a tape measure.

[1]  “Six reasons why the waist-to-height ratio is a rapid and effective
global indicator for health risks of obesity and how its use could
simplify the international public health message on obesity.” Ashwell M,
Hsieh SD. Int J Food Sci Nutr. 2005 Aug;56(5):303-7.  http://www.ncbi.nlm.nih.gov/pu…

[2] “Waist/height ratio as a simple and useful predictor of coronary heart disease risk factors in women.” Hsieh SD, Yoshinaga H. Intern Med. 1995 Dec;34(12):1147-52. https://www.jstage.jst.go.jp/a…

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