Working with mice bred with a genetic predisposition to develop breast cancer, Hardman compared the incidence rates for the disease in offspring depending upon theirs and their mothers' relative consumption of diets either high in omega-6 fatty acids, or high in omega-3 fatty acids.
The genetic make-up of the female mice was such that all would develop hyperplasia; that is, to grow too many normal cells, in the mammary ducts, by three months of age. By six months, that hyperplasia would progress to mammary adenocarcinoma.
The mice were bred and the mothers were fed diets high in either omega-6 fatty acids or high in omega-3 fatty acids, both during the gestation period and while breast-feeding the female young. After the daughters were weaned, one group was placed on a high-omega-6 fatty acid diet, while the other was fed predominantly omega-3 fatty acids.
In Hardman's experiment, all the young exposed only to omega-6 fatty acids, in utero, in nursing and after weaning, showed mammary gland tumors by six months of age. Conversely, fewer than 60 percent of the female offspring who ate richly of high omega-3 fatty acids either maternally or post-weaning formed mammary tumors by the age of eight months. Those exposed to omega-3 fatty acids both maternally and after weaning had a tumor incidence rate of just 13 percent.
The beauty of the mouse model, Hardman explains, is the ability it gives researchers to collapse an entire life-span into a matter of months, instead of years. By using mice programmed genetically to develop tumors in the mammary glands eliminates the element of chance.
Harman has observed suppression of tumor growth with as little as two percent omega-3 fatty acids in the diet.
"A couple of servings a week may be enough," she said. "A quarter of a cup of walnuts constitutes one serving."