A low dietary omega-6 to omega-3 fatty acid ratio is associated with reduced breast cancer risk. Now a new study has reported that the high omega-6 content of vegetable oils may interfere with the potentially beneficial effects of the most common vegetable omega-3 fat, alpha-linolenic acid, which is found in walnuts.
The omega-3 fatty acid alpha-linolenic acid is converted in the body to the omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid. These are the omega-3 fats found in abundance in fatty fish and which appear to protect against breast cancer. However, note that dietary alpha-linolenic acid above a certain threshold level results in no additional increases in circulating docosahexaenoic acid levels in both animals and humans.
The study referenced at the beginning of this article was designed to investigate the influence of the omega-6 fatty acid linoleic acid on the conversion of alpha-linolenic acid to eicosapentaenoic acid and docosahexaenoic acid. Linolenic acid is found in abundance in the omega-6 oils listed above. To conduct the study, the authors evaluated various combinations of dietary alpha-linolenic acid and linoleic acid in rats. The rats were fed one of 54 diets for three weeks. The diets varied in the percentage of energy (calories) provided by linoleic acid (0.07-17.1%) and alpha-linolenic acid (0.02-12.1%) by manipulating both the fat content and ratio of vegetable oils.
The peak circulating docosahexaenoic acid (>8% of total fatty acids) was produced by a narrow dietary range of 1 to 3% of calories from alpha-linolenic acid and 1-2% calories from linoleic acid. Circulating docosahexaenoic acid was suppressed to basal levels (approximately 2% of total fatty acids) at dietary intakes of total polyunsaturated fatty acids (alpha-linolenic acid plus linoleic acid) at levels above 3% of total calories.
The authors conclude that it is possible to enhance the docosahexaenoic acid status of rats fed diets containing alpha-linolenic acid as the only source of omega-3 fatty acids but only when the level of dietary polyunsaturated fatty acids is low.
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.