They both contain a fatty acid which can stop cholesterol from clogging up the arteries.

Tests on rabbits show that conjugated linoleic acid (CLA) reduces fat deposits in arterties by 30%.

Nutritionists traditionally warn against eating too many diary products because they are very high in fat.

David Kritchevsky, the American nutritionist who made the discovery, said: "I consider it God's joke."

Alternative sources

Milk contains the useful fatty acid

The finding does not mean, however, that people should rush to gorge themselves on diary products. The same fatty acid can be easily made from corn oil.

CLA has also been found in very experimental studies to help stop tumour growth, Kritchevsky said.

"It is something that is made in the cow's rumen, part of its digestive system," he said.

"Now people are desperately looking to see what else it does."

Not tested on humans

The research on rabbits found that CLA did not lower the overall amount of cholesterol in the blood but simply stopped it from settling down in the arteries.

However CLA has not been tested on humans, and Kritchevsky said his experiments in no way reflected the normal human diet.

"The amount I was feeding was a lot for a human diet," he said.

Kritchevsky said he was not advocating that people eat a lot of cheese in the hope of reducing the risk of heart disease.

"You want my advice on diet? It's moderation, balance and variety."