Microwaving food generates the cancer-causing chemical acrylamide, scientists have discovered.

Swedish research published in April revealed the food contaminant was formed by frying and baking starch-based foods.

But now chemists at Stockholm University have found heating any food containing potato in a microwave produces significant levels of acrylamide.

Acrylamide, a chemical used in industry to make a plastic component, is known to have caused nerve damage in people who have been exposed to it.

"I would say that boiling at 100 C is the only safe cooking method."

Margareta T�rnqvist

It appears to form when food reaches temperatures much higher than 100C during cooking.

The latest research, to be published in the Journal of Agricultural and Food Chemistry, is the work of a team led by Dr Margareta T�rnqvist who first discovered acrylamide in food.

She believes health is threatened by acrylamide in concentrations greater than 100 parts per billion.

Her recent experiments showed the following amounts of acrylamide in foods:

Potato crisps - nearly 4,000 parts per billion

Chips - 736 parts per billion

Microwaved grated potato - 650 parts per billion

Fried spinach - 112 parts per billion

"I would say that boiling at 100 C is the only safe cooking method," Dr T�rnqvist told 4x4 Reports.

"We found that when we heated protein-rich foods, such as beef and chicken, only moderate levels of acrylamide were produced.

"But carbohydrate-rich foods had high levels, with crisps and chips producing the most.

"And the higher the cooking temperature, the higher the level of acrylamide."

While Dr T�rnqvist was hesitant to promote mild cooking because of the dangers of food-borne diseases like Salmonella, she said the study proved overcooking should be avoided, especially with potatoes.

"We have so far only studied the carbohydrate-rich staple foods of Western society.

"But these form some of our most popular meals so food companies may have to make big changes in the way they produce food."