A new study has reported that offspring of rats fed a diet high in canola oil are less likely to develop mammary tumors than offspring of rats fed a corn oil diet. Maternal consumption of a diet high in omega-6 fats has previously been shown to increase risk of mammary gland cancer in female offspring of rats whereas a diet high in omega-3 fats from fish oil has been shown to reduce the risk. In the study, omega-3 polyunsaturated fats were increased compared to omega-6 polyunsaturated fats by using canola oil instead of corn oil in the maternal diet. Female mice were placed into one of two groups. The first group was placed on a control diet containing 10% by weight corn oil, which contains 50% omega-6 polyunsaturated fats. The second group received 10% by weight canola oil, which consists of 20% omega-6 polyunsaturated fats and 10% omega-3 polyunsaturated fats. After two weeks, the rats were bred and they continued to consume their assigned diets throughout pregnancy and nursing of the pups. After weaning, all of the female pups were given the high omega-6 corn oil diet.

Compared to offspring of mothers fed the corn oil diet, pups of mothers fed the canola oil diet had significantly fewer mammary gland tumors throughout the experiment. Tumor incidence (fraction of mice with any tumors) and total tumor weight per mouse (in mice that developed any tumors) in the offspring of the canola oil diet group was less than half that of the corn oil diet group. Maternal consumption of canola oil was associated with delayed appearance of mammary gland tumors and slowed the growth of any tumors that did develop in the offspring. The authors conclude that substituting canola oil for corn oil is an easy dietary change for people to make that might decrease risk of breast cancer in their daughters.