Bottomline: A diet high in omega-6 fat eaten during pregnancy may increase the baby’s risk for developing breast cancer, according to results of a study presented at the American Association for Cancer Research's Seventh Annual International Conference on November 18, 2008.

Background: In the 1950s and 1960s, doctors started to recommend increasing polyunsaturated fats to reduce the risk of heart disease.  Notably, omega-6 fats are the most common and dominant polyunsaturated fat in the USA. “Soon after those recommendations is when hormonally-influenced cancers - prostate, breast, colon - started going up," according to Dr. Elaine Hardman, Ph.D., associate professor of biochemistry and microbiology at Marshall University School of Medicine and lead author of the study.

Summary: Hardman’s research team fed one group of pregnant mice a diet containing corn oil. Corn oil was used to evaluate the risk of developing breast cancer, because of it’s high omega-6 fat content and it reflects the omega-6 fat content of the American diet. The other group was fed a canola oil based diet. Canola oil was used because of its lower omega-6 fat content and its availability.  After weaning, all offspring were fed a diet containing corn oil. Next the incidence of breast cancer and changes to breast cancer regulating genes in the offspring were evaluated.

While both groups of offspring were about the same weight, the total tumor weight, number of glands with tumors and fraction of mice with tumors were higher in those whose mothers who were fed corn oil.   The researchers found changes in gene expression up to five months after the animals were exposed to a diet containing omega 6 fatty acids during gestation and lactation. 

Hardman theorizes that during gestation and lactation, the mother's diet must be imprinting the genes of the baby.  The canola oil group displayed up-regulated genes and transcription factors that influence tumor suppression. 

Scientist Quote: "This is a slam-dunk easy change for people to make," said Hardman. "Canola oil is readily available on the grocery shelf, doesn't cost any more than corn oil, and we can use it for all the things we use corn oil. It will help correct some of the omega 3 and omega 6 imbalance. And by changing the mother's diet, we might be able to reduce cancer in the next generation."

Comments:  These results demonstrate new mechanisms by which omega-6 fats may promote breast cancer--a nutrient gene interaction.  These findings are also consistent with two human studies.  See:

•  Omega-6 Fat May Promote Breast Cancer Development
  

•  Another New Breast Cancer Study: Omega-6 Fat Increases Risk Two-fold in Large U.S. Study).

While canola oil is much lower in omega-6 fat than corn oil (See Foods High in Omega-6 Fat), you can lower omega-6 fat even further by switching to olive oil, for use in cooking, marinades and salad dressing.  Olive oil has half the amount of omega-6 fat compared to canola oil--1320 versus 2840 milligrams, per tablespoon, respectively. 

Sources:
American Association for Cancer Research's Seventh Annual International Conference.