Date:   11/16/2008 12:57:35 PM ( 16 y ago)
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Waisting away: you and your BMI index
For years we have been told that the most accurate indication of being healthy is a good body mass index (BMI.


By Janette Marshall
Last Updated: 12:33PM GMT 16 Nov 2008
Two overweight women: Waisting away: you and your BMI index
Many are deluded about how much they weigh Photo: Ian Jones

First developed 100 years ago, it is the measure used by doctors' surgeries, insurance companies and slimming clubs. But last week researchers from Imperial College, London and the German Institute of Nutrition released details of a landmark study showing that a large waistline can increase the risk of premature death – even for people who have a healthy BMI.

In fact, every 2in increase in waist circumference increases men's risk of dying early by up to 17 per cent.

"The vast scale of numbers – more than 350,000 people from nine countries in Europe monitored for 10 years – and the degree of risk shown is astonishing," says Dr David Haslam, clinical director of the National Obesity Forum, commenting on the findings of the European Investigation into Cancer and Nutrition (Epic).

"Abdominal fat is like a giant gland secreting hormones and toxic chemicals that contain inflammatory agents that act on the liver, bowel and arteries to the heart."

The study highlighted a doubling of the risk of death in men whose waists exceed 47in, compared to those whose waists were under 31.5in, and similar findings for women with waists over 39in, compared to those under 25.5in.

But, worryingly, two recent pieces of research have shown that many people increasingly fail to recognise they have either a weight – or a waist – problem.

Earlier this year researchers at Leicester University asked 500 people to estimate their waist size. They found that men commonly underestimated their waist by an average of 3.1in and women by an average of 2.2in.
APPLES AND PEARS

Similarly, a study from the Health Behaviour Research Centre at University College London showed that overweight people were less likely in 2007 to consider themselves overweight than in 1999.

Then, 43 per cent of those surveyed had a BMI (calculated by dividing weight by height squared – see below) that put them in the overweight or obese range, of whom four fifths correctly identified themselves as overweight. But by 2007, 53 per cent of the population had moved into the overweight range but only three quarters of themselves realised this.

Where your body deposits fat is genetically controlled, with some overweight people becoming "apples" when fat goes on the stomach, and others becoming "pears", when weight goes on the hips and thighs, says Helen Stracey, dietician and spokesperson for the British Dietetic Association.

Fat can also be deposited around the heart, liver and kidneys when it's called visceral fat. "Visceral fat can be present in people with a healthy BMI and who appear slim," says Stracey.

Fat also tends to be deposited on the waist more with age. "This is due to hormonal changes in women after the menopause. Most men tend to be apples anyway," says Dr Margaret Ashwell, former science director of the British Nutrition Foundation.

"With a fall in oestrogen and rise in testosterone, even women who are pears tend to become apples when they put on weight." Both abdominal and visceral fat are harmful, contributing to heart disease and Type 2 diabetes, because they cause inflammation that can damage blood vessels and disturb glucose metabolism, she adds.
DANGER ZONE

But, warns Professor Steve Field, chair of the Royal College of GPs, we can't just blame our genes or our age. "Environment is far more important than genetics and other factors. Lack of exercise, eating too much and a sedentary lifestyle are to blame."

The danger is that believing yourself slimmer than you are can delay diagnosis for Type 2 diabetes, warns Zoe Harrison of Diabetes UK – which increases the risk of complications such as heart disease, stroke, blindness, kidney disease and amputation.

"The danger zone on the tape measure for diabetes is slightly lower for people of Asian and black origin, who are at risk from age 25, compared with the white population who should pay particular attention to their waist measurement aged 40 and over," says Harrison. "Eighty per cent of people diagnosed with Type 2 diabetes are overweight, and abdominal fat is a risk factor for the condition."
WAIST AGAINST HEIGHT

The reasons for this include variations in size and body frame between ethnic groups contribute to different "at risk" waist measurements. Other theories for higher risk of Type 2 diabetes include intrinsic genetic differences in insulin resistance, and change from traditional to Western diet when populations move.

The good news is, that eating less and taking more exercise can whittle away the waist, says Stracey. "The problem is that there is no magic way to target stomach or visceral fat separately. To lose any body fat you need to do up to an hour's exercise a day and eat fewer calories than you use."

Even if you appear slim, visceral fat will go if you reduce body fat in general, "although specific exercises aimed at the abdomen and core will help speed up the process", says Stracey.

As an alternative to the BMI, Dr Margaret Ashwell, has developed a chart that plots waist against height (www.ashwell.uk.com/shapechart.pdf) as a more accurate measurement of whether you are at an advisable weight. "I advise keeping your waist less than half your height and this applies to all ages and ethnic groups and to both men and women," she says.

Meanwhile, the Epic researchers urge GPs to routinely measure patients' waists. "Many do already," says Prof Field. "Although it's something patients can do for themselves."

But all too often – whether through ignorance or cheating – we don't measure correctly, he warns.

"Measure your waist at the mid-point between the top of your pelvis [hip bones] and the bottom of your rib cage. Put the tape round the middle, parallel to the floor – and not beneath your beer belly."

HOW DO YOU MEASURE UP?

To work out BMI

Divide your weight in kilograms by height in metres squared.

Normal: 18.5 – 24.9

Overweight: 25 – 29.9

Obese: Above 30

To work out waist-to-hip ratio

Divide your waist measurement by the hip measurement. If the ratio of your waist to hip measurement is more than 0.95 as a man and 0.87 as a woman you are apple shaped and overweight and therefore at risk.

Risk of diabetes:

Diabetes UK advises that if your waist measurement is higher than the following, and you fall into the above age categories, you should ask your GP for a test for diabetes:

Women: 31.5in (80cm) and above

White men and black men: 37in (94cm) and above

South Asian men: 35in (90cm) and above



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