But experts have suggested that other warnings about the high salt content of soy sauce could confuse people aiming to improve their diet.

Both high levels of cholesterol in the blood, and high blood pressure are contributory factors in the development of coronary heart disease.

A large salt intake has been shown to increase blood pressure.

But the latest research has found that some soy, containing substances called "isoflavones", can produce "dramatic declines" in cholesterol.

Patients with high cholesterol levels given soy containing large amounts of the isoflavones found their levels reduced by 10%.

Even half that concentration resulted in a significant reduction.

Heart disease low in Asia

Studies suggest that people in Asian countries consume roughly 30 to 50 times more soy than in Western Countries.

People in those countries not only have low levels of cardiovascular disease, but also breast and uterine cancer, although it cannot be proven that soy is exclusively responsible for these benefits, as the average Asian diet is far removed from that in the West.

The US researchers, writing in the Archives of Internal Medicine journal, even found that blood pressure dropped among females given higher doses of isoflavones.

However, a UK expert said that consumers were being bombarded with confusing messages about healthy diet.

Soy is often named as a food which is high in salt, and the public are urged to keep their salt consumption down - or risk heart disease.

Dr Mark Davis, a Leeds GP who is chairman of the Primary Care Cardiovascular Society, said patients should wait until evidence that any benefits outweigh risks has arrived.

He said: "I think it is confusing, and commercial interests do tend to get involved in this kind of thing.