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updated 4/28/2010 6:56:07 PM ET 2010-04-28T22:56:07

While cancer victims usually blame themselves — I shouldn't have smoked, should have eaten better, should have exercised — or the cruelty of chance, they may now have a new scapegoat: Grandma.

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Eating poorly during pregnancy can increase your children's and your grandchildren's risk of cancer, even if they themselves eat healthily, a new study on rats suggests.

The risk associated with high-fat diets, especially those high in omega-6 fatty acids, "can be passed from one generation to another without any further exposure," said lead researcher Sonia de Assis of Georgetown University.

While done in rats, the diets used by the study mirrored some typical American eating habits, and so the researchers suspect the results could hold for humans as well.

The research was presented last week at the American Association for Cancer Research's annual meeting in Washington D.C.

During the study, some pregnant rats were fed a diet high in omega-6 fat while others received standard fare. After the babies were delivered, all the mothers, their children and their eventual grandchildren ate healthy moderate-fat diets.

Granddaughters of the rats that gobbled excess fat during pregnancy had a 30-percent greater chance of developing breast cancer than those with grandparents who ate healthfully. When only one grandmother, on either the mother's or father's side, had indulged, the granddaughter's disease risk was 19-percent higher.

For the high-fat diet, the study used a chow that was 43-percent fat, predominantly from omega-6 rich vegetable oil. Most recommendations for a healthy diet include keeping fat intake at 25 to 30 percent, de Assis told LiveScience, "but with fast foods and everything, a lot of people eat more than that each day."

Fat gone rogue
This should not imply that fat causes cancer — many fats are quite good for you, after all. But it is more bad news for omega-6 fatty acids, found in corn oil and most non-grass-fed meats.

Omega 6s, while essential to a healthy diet, should be balanced with omega 3s. The optimum ratio of omega 6 to omega 3 is likely between 4:1 to 1:1, but in the typical American diet the ratio is more like between 20 and 16:1. This imbalance has previously been linked to a host of health problems, including depression, infertility, heart disease and, yes, cancer.

In the new study, the researchers theorize the increased cancer risk might be a result of the epigenetic effects of omega-6 fats. (Epigenetics refers to the idea that even if genes themselves aren't altered, how they function can change.) Omega 6s may indirectly turn off genes that slow cell apoptosis (normal cell death). Cells can then proliferate and lead to tumors, which are essentially a bundle of multiplying cells gone wild.

Somehow, the fat must also be affecting the "germ line," the pathways that lead to viable sperm and eggs, for the effect to be crossing multiple generations.

DNA is not in the driver's seat
Epigenome, which literally means "on top of the genome," refers to all the factors that control how a gene is expressed. The new study potentially adds to the growing body of research suggesting the epigenome may be at the root of many health problems.

"People think there is nothing you can do (about your disease risk)," said researcher Rod Dashwood of Oregon State University, who gave a lecture on epigenetics at the Experimental Biology 2010 conference in Anaheim, Calif. "But you are not just what your genes are." (Dashwood has conducted separate research from de Assis.)

Rather, you are your genes under the influence of your epigenome, which, during critical periods, is shaped by your environment, your lifestyle, your life experience — and those of your immediate ancestors.

"Genes only account for 5 to 10 percent of the familial risk of breast cancer," said de Assis, by way of illustration. Something inherited in the epigenome could account for the rest.

Take hold of the steering wheel
For decades, studies have been associating diet with disease risk. Now, research on the epigenome may be revealing the mechanism at play.

For example, Dashwood's work indicates that many whole foods — including broccoli sprouts, onions, garlic, radishes, wasabi, daikon, horseradish and wheat bran — may help prevent epigenetic processes that lead to degenerative diseases, such as cancer, heart disease, stroke and even aging.

"The (epigenetic) effect may be contributing to the overall health benefits of these particular foods," Dashwood told LiveScience.

While the multi-generational impact of veggies has not been studied, Dashwood said, "some epigenetic marks can go through six, seven generations."

More research is needed but the lunchroom choice between a bacon-cheeseburger or stir-fry may not only affect your own health, but that of your children and grandchildren.

© 2012 LiveScience.com. All rights reserved.

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