THE key to a long life is having a waist no bigger than half your height, according to a new scientific study.
The report, to be published tomorrow, is based on 20 years of British medical records and is the first to quantify how many years you will lose to obesity as measured by your waist-to-height ratio.
Dr Margaret Ashwell, a co-author of the study, said the rule applied regardless of a person’s age, ethnicity or gender. She added that the evidence was so strong that it should provide the basis for a simple global health check, which anybody could perform with a piece of string if they did not have a tape measure: “Keep your waist circumference to less than half your height.”
The waist is the halfway point between the lowest rib and the hip bone, although researchers say it is good enough to measure the narrowest point — just do not breathe in.
Advertisement
The study by Ashwell and researchers from City University London’s Cass Business School is the first to analyse official health records and measure the impact on life expectancy of obesity, as measured by the ratio between your waist and height.
Mr Average, a 30-year-old man who is 5ft 10in tall, should have a waist of no more than 35in — but if that expands to 42in, or 60% of his height, he will lose 1.7 years. His female counterpart, who is 5ft 4 in tall, will die 1.4 years prematurely if she lets her waist expand from half her height, 32in, to 60% of her height, 38.4in.
The penalty in a reduced life span is much more severe for those who become seriously obese.
A man aged 30, of average height and a 56in waist, can expect to lose 20.2 years, while an obese woman of 30 with a waist of 51in will die 10.6 years early. However, only 0.2% to 0.3% of that age group are so excessively overweight.
The study also tracked the impact on 50 and 70-year-olds and found that they, too, sacrificed years from their lives by letting their waists exceed half their height. Fewer years will be lost, largely because their remaining life expectancy was lower to start with.
Advertisement
Ashwell, who in 1996 popularised the discovery that “apple-shaped” obesity is much more dangerous than “pear-shaped”, said the circumference of the waist is important because it indicates the amount of “central fat” in the body. This affects the vital organs, causing health problems from heart trouble to diabetes, unlike fat around the thighs, hips and bottom.
The findings will put pressure on the government to use waist-to-height ratio to assess the true threat of obesity. Ashwell said the proportion of adults at risk on this measure was 69% rather than the official estimate of 56%, which uses a ¬combination of waist circumference and body mass index (BMI).
She added: “People are living in false hope if they rely on their BMI figure. We have got to measure the right thing.”
Critics of BMI have long pointed out that it does not distinguish between fat and muscle. Arnold Schwarzenegger and Danny DeVito, co-stars of the 1988 movie Twins, had the same BMI, implying they would die 3.6 years early, whereas, if measured by their waist-to-height ratio, Schwarzenegger was in good health while DeVito’s excess fat meant he would lose 5.8 years.
The study demonstrates that BMI is particularly poor at predicting early death from obesity for women, while waist to height provides ¬accurate estimates for both sexes.
Advertisement
Cass examined morbidity and mortality figures as well as the Health and Lifestyle Survey, which has tracked a random sample of the population since 1985 on a range of measures including weight, height, waist measurement, diet and exercise. Researchers excluded smokers to avoid distorting the results.
Les Mayhew, professor of statistics at Cass, said: “There is now overwhelming evidence that government policy should place greater emphasis on waist-to-height ratio as a screening tool.”
The Institute and Faculty of Actuaries funded the early stages of the research, which will be published by the Public Library of Science.
The professional body representing GPs, which recently declared a state of emergency on childhood obesity, welcomed the findings but said it was unclear whether “worrying people about their weight actually motivates them to make a long-term commitment to lifestyle changes”.
Dr Rachel Pryke, clinical spokeswoman on nutrition at the Royal College of General Practitioners, said: “While there have been big investments in obesity prevention strategies, there is an urgent need for research that shows us how to tackle established obesity — in particular childhood obesity — and how we can support our patients to manage both their own weight and the weight of their children.”