Fish Oil and Certain Species of Fish May Negate the Effects of Chemotherapy

SUMMARY: It is estimated that approximately 20% of cancer patients in the US take Omega-3 fatty acids in the form of fish oil. Fish oil is a mixture of fatty acids produced from several species of fish and the two most abundant and important fatty acids in fish oil include EicosaPentaenoic Acid (EPA) and DocosaHexaenoic Acid (DHA). Fish oil content in presently available preparations is not standardized and does not require FDA approval. Preclinical studies have demonstrated that mouse tumors recruit mesenchymal stem cells that are specifically activated by platinum based chemotherapy and secrete 2 fatty acids, 12S-HHT and 16:4(n-3)). These fatty acids are called Platinum Induced Fatty Acids (PIFAs) and they have been shown to induce resistance to a broad range of chemotherapeutic agents, by activating a cytoprotective response in the tumor tissue. Fish oil has relevant levels of fatty acid 16:4(n-3) and preclinical models have shown that the fish oil neutralized the antitumor activity of chemotherapy, thus conferring drug resistance. With this preclinical information and given that cancer patients frequently use fish oil supplements, the authors evaluated the effect of fish oil intake in healthy volunteers, on the plasma levels of fatty acid 16:4(n-3), which has been shown to induce resistance to chemotherapeutic agents. The researchers first conducted a survey to determine what percentage of cancer patients undergoing treatment at a University Medical Center in the Netherlands were taking fish oil supplements. They also analyzed fatty acid 16:4(n-3) content, in 3 brands of fish oil supplements and 4 often consumed species of fish. The authors then randomly selected 30 healthy volunteers for the fish oil study and 20 healthy volunteers for the fish consumption study and the plasma levels of fatty acid 16:4(n-3) was measured after they consumed fish oil or fish, for a period of 2 weeks. They noted that 11% of the cancer patients in their study reported using omega-3 supplements. All fish oils tested contained amounts of fatty acid 16:4(n-3) ranging from 0.2 to 5.7 μM and this was adequate to induce chemoresistance to a variety of chemotherapeutic agents. They noted that there was a significant rise in the plasma 16:4(n-3) fatty acid levels in the healthy volunteers after they consumed fish oil supplements and fish, with high levels of fatty acid 16:4(n-3). Herring and Mackerel fish contained high levels of fatty acid 16:4(n-3), in contrast to Salmon and Tuna. The authors concluded that based on this preclinical data it is best to avoid fish oils and fish such as Herring and Mackerel in the 48 hours surrounding chemotherapy, as the high plasma 16:4(n-3) fatty acid levels may negate the effects of chemotherapy. These recommendations have been adopted by the Dutch Cancer Society and by the Dutch National Working Group for Oncologic Dieticians. Increased Plasma Levels of Chemoresistance-Inducing Fatty Acid 16:4(n-3) After Consumption of Fish and Fish Oil. Daenen LGM, Cirkel GA, Houthuijzen JM, et al. JAMA Oncol. 2015;1:350-358