A new study has reported that the dietary ratio of omega-3 to omega-6 fats influences breast density and breast cancer risk in an animal model of breast cancer. Higher omega-3 to omega-6 diets reduced mammary gland density, which reduced carcinogen-induced mammary tumor development. To conduct the study, a diet was developed for rats that provided 30% of dietary calories from fat and could be formulated to contain ratios of omega-3 to omega-6 fatty acids ranging from 25:1 to 1:25. Mammary tumors were induced in female rats by a carcinogen. Mammary gland density was found to decline in a dose dependent manner with higher omega-3 to omega-6 ratios. A 20.3% difference in mammary gland density was observed between diets with ratios of 1:1 compared to 25:1. The authors confirmed that mammary tumor development in the animals was inhibited in a manner predicted by mammary gland density in the absence or presence of tamoxifen.

Circulating omega-3 fatty acid concentrations did not increase above an omega-3 to omega-6 ratio of 5:1 even when the dietary ratio was far higher. Higher omega-3 to omega-6 ratios reduced plasma leptin and increased adiponectin, indicating that fat tissue function was influenced in ways that would tend to inhibit tumor growth (leptin has been shown to stimulate breast cancer cell proliferations whereas adiponectin suppresses it). However, neither leptin nor adiponectin was predictive of mammary gland density. On the other hand, circulating insulin-like growth factor-I (IGF-I) declined with increasing dietary omega-3 to omega-6 ratio and was predictive of the observed changes in mammary gland density. IGF-1 is required for mammary development at puberty and has been implicated in increased risk of breast cancer.

Comments regarding the study

The U.S. diet tends to supply an abundance of omega-6 fatty acids, whereas consumers have to make a special effort to obtain omega-3s. While beneficial, the trend away from animal fats (such as lard) and partially hydrogenated oils in processed foods and fast food meals has left the false impression that high omega-6 fats such as soybean oil and corn oil are "healthy." Reducing consumption of omega-6 fats can be an important part of a strategy to improve your dietary fat ratio.

Please see our article on how to optimize your breast cancer diet for information on what to eat during all stages of treatment and recovery.