US fast food giant McDonald's says it is changing the oil it uses to cook its French fries, in an attempt to make them healthier.

The hamburger chain says the move at its US locations has been in the works for years and is unrelated to a recent lawsuit by people who claim fast food has harmed their health.

It is not the first time McDonald's has changed its French-fry cooking oil.

In 1990, as US consumers became more health conscious, the restaurant switched from beef to vegetable oil in order to reduce cholesterol levels in its foods.

If we can get rid of trans fat in the diet, we could prevent thousands of heart attacks every year

Dr Meir Stampfer

That move saw the firm caught up in a legal fight with vegetarians in which it was forced to admit that there was still beef fat used in its fries for flavouring.

The latest move will see McDonald's switch to an oil that will result in fries that are just as fatty, but which have different kinds of fats that experts say are healthier.

McDonald's says the new oil will mean fries with 48% fewer trans fatty acids, and 16% less saturated fat.

Polyunsaturated fats will rise by 167%, but health experts say the change can help lower cholesterol levels.

'Win-win'

Dr Meir Stampfer of the Harvard School of Public Health hailed the move, but said he hoped McDonalds's and other fast food chains would eliminate all trans fatty acids from their menus.

McDonald's says it serves 46 million people a day around the world

"If we can get rid of trans fat in the diet, we could prevent thousands of heart attacks every year," he told AP.

All 13,000 US McDonald's outlets will be using the new oil by February 2003, but the fast-food chain's executives say the fries' taste will not change.

"It's a win-win for our customers because they are getting the same great French-fry taste along with an even healthier nutrition profile," said Mike Roberts, president of McDonald's USA, in a statement.

McDonald's said it hopes to have all of its restaurants around the world using fewer trans fatty acids in the future, but noted that the changes in the US will bring its locations there in line with McDonald's restaurants in Europe, which already use similar oils.

In July, a group of overweight Americans filed a lawsuit in a New York court, accusing McDonald's and other US fast food chains of enticing consumers into eating extremely unhealthy food.

A recent study found that more than half of all adult Americans were overweight.