String theory


“How long is a piece of string” is a typical response when there is uncertainty as to how long a task might take. Anyone ever trying to set a deadline with a builder or IT developer will appreciate the challenge – the realm of uncertainty defeating even the most well-meaning intentions. Yet the length of a piece of string turns out to be a better predictor of our health than BMI.

Key health indicators

Epidemiologists’ tell us that some three quarters of the variation in life expectancy between countries can be explained by key risk factors, with much more due to the sociocultural environment than to their genes or the physical environment. The big factors in how people live their lives are:

  • whether they smoke
  • what and how much they eat
  • whether they abuse alcohol or drugs.

These, along with high levels of blood sugar and blood pressure, both of which are heavily influenced by diet, are the main factors dictating poor health.

Our aim should be to live free of chronic disease and disability well into old age — in other words, to maximize the chances of adding both years to life and life to our years.

Doesn’t BMI help guide us?

BMI stands for Body Mass Index. An important measure in the eyes of the health profession when it comes to evaluating health, it’s a simple calculation of your weight (in kilos) divided by your height (in metres) squared to give you a value; this is then placed on a spectrum to see whether an individual is underweight, healthy weight, overweight or obese.

The problem with BMI is that this calculation is far too simplified, while it turns out the value is at best pretty worthless, at worst misleading.

Your weight is a better indicator

Why? Mainly because BMI doesn’t allow enough variables to be accounted for to present an accurate view on health. For example, whether an individual is made up of predominantly body fat or lean body mass will have a huge impact on health and fitness. Yet it’s possible for an individual to have too much fat and not enough lean body mass but have a healthy weight score for their BMI. Equally, muscular individuals with low levels of body fat might be categorised as overweight or obese. Many now believe it’s a discredited and rather nonsensical number, particularly when considering the wide range of bodies in modern society. A case of one number fitting none.

The importance of Body Composition

Body Composition (BC) is a very different proposition. This is a measure to determine the body’s make-up, determining levels of body fat or lean body mass – a potentially helpful value.

There are many methods of calculating BC, with some better than others. They include BIA (Bioelectrical Impendence Analysis), the Bod Pod, calliper skin fold testing and the Hydrostatic method. Some produce a value accurate to within a 10-15% range, with the most accurate being hydrostatic producing accuracy to within 1%.

All of them calculate a body fat percentage and an amount of lean body mass. Usually the lower the body fat percentage the better, until you reach lower single digits, which is unhealthy. Women should have more body fat than men to maintain optimal health. Generally, the higher the amount of lean body mass you have relative to fat, the better and healthier – with lean body mass accounting for everything else – bones, organs and muscles.

So, where does the string come in?

BC is a vastly superior measure in establishing our health and fitness in comparison to BMI, and while it can be more challenging to calculate accurately, one extraordinarily simple measure is a good guide and a better predictor of our health prospects than BMI.

In their paper Waist-to-Height Ratio Is More Predictive of Years of Life Lost than Body Mass Index, authors Margaret Ashwell, Les Mayhew, Jon Richardson and Ben Rickayzen, after analysing the number of lives lost at three age levels (30, 50 and 70) by comparing the life expectancies of obese lives with those at optimum levels of BMI and Waist-to-Height ratio (WHtR) they found WHtR was a better predictor of mortality risk. And for the first-time years of lost life were quantified for different values of WHtR. And the simple way to test yourself is by using a piece of string.

Taking the String Test

All you need do is measure out a piece of string to match your height. Then fold it in two and put it round your waist. This fun video shows you how.

If the string doesn’t make it around your waist, this will be a warning about how much damaging visceral fat you are carrying. However, if the string fits around the waist – or is even loose, your waist to height ratio is where it should be.

To help add years to your life, keep your waist circumference to less than half your height.

A final point: whatever the measure you choose, don’t become fixated upon it. Measure it occasionally, if you believe it will help motivate you, but don’t waste too much time on it – concentrate on eating smarter, exercise daily and making sure you get enough sleep.

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Iris is the founder of No Targets Just Routine. She has researched food since 2009 and believes “Happiness is real food shared with loved ones.”

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