Waist circumference, rather than overall weight, is the truest indicator of an increased risk of diabetes or heart disease, a leading British health expert said on Wednesday.

Although being overweight raises susceptibility to certain illnesses, the main threat to health lies in where the extra weight is carried.

Fat deposited on the stomach or abdomen, the classic beer gut, is more dangerous than extra pounds on the thighs because the fat cells around the waist pump out chemicals that can damage the insulin system - raising the risk of diabetes and heart disease.

“Waist circumference can predict the risks of type 2 diabetes and heart disease more accurately than weight,” Professor Anthony Barnett of the University of Birmingham told an obesity conference.

“Thicker waistlines may double to quadruple the risks, compared to those with slimmer waistlines.”

Barnett told a meeting of the National Obesity Forum in London that if obesity continues at the current rate, 10 percent of the British population will suffer from diabetes and related complications in the next decade.

“Men with waists of more than 40 inches (101 cm) and women with waist measurements of more than 35 inches (89 cm) are at an incredibly high risk of type 2 diabetes and heart disease,” Barnett said.

Diabetes is caused by a deficiency or lack of insulin. People with type 1 diabetes do not produce any insulin and need daily injections. Type 2 diabetes, the most common type of the disease, is caused by an inability to make enough, or to properly use insulin.

Insulin helps the glucose from food get into cells. If a person does not produce enough or if it isn’t used properly by the body, glucose stays in the blood. The larger a person’s waistline, the more resistant they become to insulin.

“The more resistant you are to insulin, the more insulin the body has to produce from the pancreas gland in order to have the same effect,” Barnett added. “Eventually the pancreas becomes exhausted and either stops producing as much insulin, or, in severe cases, may stop producing insulin altogether.”

Bulging waistlines can also increase the risk of high blood pressure and raised cholesterol levels.