"This is really good news," said Dr. Jacques Rossouw of the National Institutes of Health, which funded the work. "But you have to stick with the diet."

It's arguably the most promising finding of the mammoth Women's Health Initiative dietary study, which enrolled tens of thousands of healthy women ages 50 to 79 to track the role of fat in several leading killers. Some women were assigned to cut the total fat in their diets to 20 per cent of calories -- from an average of 35 per cent -- while others continued their usual diets for comparison.