LONDON (Reuters) - Diets high in fat are well known for causing blocked arteries but Canadian researchers have shown they can also impair memory in rats, New Scientist magazine reported on Wednesday.

Studies of adolescent rats which had been fed diets rich in animal and vegetable fats since birth showed they did not perform trained tasks as well as lean rodents raised on a more balanced diet.

``High-fat diets impair performance on virtually all our measures,'' said Gordon Winocur of the Baycrest Center for Geriatric Care in Toronto.

``It's remarkable how impaired these animals are.''

Winocur and his colleagues suspect the fat interferes with insulin and prevents the brain from using glucose. They are concerned that the high fat diet preferred by most teenagers could be damaging pathways in the brain.

``And maybe the developing brain is much more susceptible than the older brain,'' Winocur added.