The key to living longer is having a waist measurement no bigger than half your height, according to research.
Scientists have devised a simple formula which predicts how many years of life someone will lose to obesity.
And they claim the rule applies regardless of age, gender or ethnicity.
It is worked out by measuring around the waist – technically between the lowest rib and hip bone – making sure you do not breathe in.
As long as this is half your height or less, you should live to the average life expectancy – which is currently around 81. But for every few inches over, you face losing months or even years of life.
For example, an average 30-year-old man who is 5ft 10in tall – or 70 inches – should have a waist size no bigger than 35 inches. A 30-year-old 5ft 4in woman should have a waist size of 32 inches or under.
But if the man’s waist size expands to 42 inches – or 60 per cent of his height – it will knock 1.7 years off his life, according to the formula. Likewise if the woman’s waist grows to 38.4 inches she will lose 1.4 years.
This may not sound much but it quickly adds up if someone is severely obese.
A 30-year-old man of 5ft 10in with a 56-inch waist can expect to lose 20.2 years from his life expectancy. Similarly a woman with a 51-inch waist will die 10.6 years earlier.
The researchers at Cass Business School at City University, London, came up with the calculation after looking at records of more than 300,000 adults spanning 20 years. Dr Margaret Ashwell said it should be used as a simple health check that anyone can do at home.
She added that waist circumference is important because it shows the amount of central fat in the body – which is linked to high cholesterol, diabetes and heart disease. She also believes the waist-to-height ratio is a far more reliable predictor of ill health and obesity than the Body Mass Index (BMI) – which is widely used by doctors.
‘People are living in false hope if they rely on their BMI figure. We have got to measure the right thing,’ she said.
The BMI compares a person’s weight to their height.
Professor Les Mayhew, who was also involved in the study to be published by the Public Library of Science, said: ‘There is now overwhelming evidence there should place greater emphasis on waist-to-height ratio as a screening tool.’
However Dr Rachel Pryke, clinical spokesman on nutrition at the Royal College of GPs, said it was unclear whether ‘worrying people about their weight actually motivates them to make a long-term commitment to lifestyle changes’.