A new prospective study has reported that the relative level of omega-6 compared to marine omega-3 fats in the diet is related to risk of breast cancer whereas the absolute levels of these fats is not. The study was designed to investigate the associations between polyunsaturated fatty acids (PUFAs) and the ratio of omega-6 PUFAs to marine omega-3 fats (i.e., those found in fish oil) and risk of breast cancer. The study included 72,571 initially cancer-free participants in the Shanghai Women's Health Study. Fat consumption was determined using food questionnaires. PUFA intake levels of the women in the study were grouped into thirds. A total of 712 breast cancer cases were diagnosed during follow up.
The authors found no relationships between dietary intake of linoleic acid, arachidonic acid, α-linolenic acid, or marine omega-3 PUFAs (docosahexaenoic acid and eicosapentaenoic acid) and risk of breast cancer. However, a significant association was found between omega-6 intake, marine omega-3 intake and risk of breast cancer. Women with the lowest intake (the lowest third consumption level) of marine omega-3 fats and the highest intake (the highest third) of omega-6 fats were found to have double the risk of breast cancer of women who had both the highest marine omega-3 fat intake and lowest omega-6 fat intake. The authors conclude that the ratio of omega-6 to marine omega-3 fats in the diet may be more important for breast cancer risk than individual dietary amounts of these fatty acids.
Other studies have also found association with high omega-6/omega-3 ratio
This is not the first report that a relatively high omega-6/omega-3 ratio in the diet may increase the risk of breast cancer. For U.S. women, this means it would be wise to increase the level of omega-3 fats in the diet since commercially produced food and restaurant food tend to have relatively high levels of omega-6 fatty acids. Processed food companies and restaurant chains participating in the ongoing move away from partially hydrogented fats typically are substituting vegetable oils. However, these oils have been shown to promote breast cancer in the laboratory and certainly contribute to the typically high levels of omega-6 fatty acids in our diets. Below are sources of high omega-6 fats that have also been found to be associated with increased risk of breast cancer, as well as high omega-3 foods that have also been shown to have preventive actions.