A tape measure could be a better guide to future health risks than bathroom scales, health experts have said.
Waist measurement is more important than overall weight, experts say
Carrying fat around the stomach can quadruple the risk of diabetes and heart disease, the University of Birmingham scientists said.
Professor Anthony Barnett said fat cells which develop round the waist pump out chemicals which damage the insulin system.
Women with waists over 35ins and 40in-waists on men are classed as high risk.
And it is these measurements rather than overall weight which experts believe are the best predictor of future health problems.
Larger waists - a beer gut or apple shape - are traditionally assumed to develop on men, whereas women are thought to carry weight on the thighs - known as pear shaped.
But scientists will tell the National Obesity Forum conference on Wednesday and Thursday that both men and women are at risk of ill health through weight gain of this type.
Prof Barnett said: "Waist measurements can predict the risks of Type 2 diabetes and heart disease more accurately than weight.
"Men with waists of more than 40ins and women with waist measurements of more than 35ins are at an incredibly high risk of Type 2 diabetes and heart
"Thicker waistlines may double to quadruple these risks, compared to those with slimmer waistlines.
"Even a lower waist of 37ins in men and 32ins in women may significantly raise the risk of either of these diseases, if not both."
Prof Barnett and his colleagues have been at the forefront of research into the understanding that fat cells around the waistline are not passive lumps of
lard but are highly active, pumping out proteins and hormones.
While in small doses these are necessary, in excess then can cause damage to insulin use, also raising blood pressure and increasing cholesterol in the bloodstream.
The number of people with Type 2 diabetes has increased significantly in recent years and now tops 1.8m.
It is caused by insulin resistance, which can be triggered by excess weight around the abdomen.
Insulin produced in the pancreas stops working properly in overweight and obese people and the fatter someone becomes, the more resistant to insulin they become.
Dr Ian Campbell, chairman of the National Obesity Forum, told BBC News Online the evidence was "overwhelming".
"People with large waists are just as at risk of those who are clinically obese.
"It may be that you are obese but have a narrow waist and not be at too much risk.
And he said while doctors were "getting to grips" with the theory that abdominal weight was the key factor in diabetes and heart disease, people should keep an eye on their own waistlines.
"Measuring your waist is a useful tool in making sure you remain healthy in the future, as a rough rule if you lose 1cm off your waist you lose about 1kg in weight.
Diabetes UK also acknowledged weight around the waist was a contributing factor in Type 2 diabetes.
A spokeswoman said: "Abdominal weight is a problem but the public are still not aware enough about the risks."