Judging by the results of cell and animal experiments, omega-3s hold promise as allies in treatment and prevention of certain cancers.
Lab studies show increased death of cancer cells and less cancer-induced wasting in animals given fish oil.
And while the clinical evidence is mixed, some small trials found that patients taking fish oil suffered less cancer-induced wasting (Baracos VE et al. 2004).
(Likewise, omega-3s seems to reduce wasting seen in one kind of heart disease … see “Fish Oil May Help Congestive Heart Failure Patients”.) 
Clinical evidence also shows low blood levels of omega-3s in newly diagnosed cancer patients and those undergoing chemotherapy (Baracos VE et al. 2004; Murphy RA et al. 2010).
Some researchers speculate that patients' omega-3 levels may be reduced by chemo drugs, as well as by the disease itself.
This lack of omega-3s is of special concern in view of substantial evidence from cell and animal studies showing that omega-3 fish oil can do several desirable things:
  • Encourage normal cell differentiation, which retards cancers
  • Reduce the wasting associated with cancer, called cachexia
  • Raise the rate at which cancer cells die from a suicidal process called apoptosis.
  • Influence gene switches related to inflammation (PPAR-gamma, NF-kB) in ways that discourage tumor growth
As the authors of one evidence review wrote, “Dietary supplementation to maintain and replenish omega-3 status at key points in the cancer disease trajectory may provide additional health benefits and an enhanced quality of life.” (Baracos VE et al. 2004)
Since then, even more lab and epidemiological evidence supports that hope.
But the results of non-clinical studies, although generally encouraging, seem unlikely to prompt official U.S. bodies to endorse omega-3s for cancer prevention or treatment (AHRQ 2005).
Now, the results of a small trial from Canada add more clinical evidence on the positive side of the scale.
Chemotherapy can cause cancer patients to lose muscle mass and become malnourished, leading to fatigue, lesser quality of life, inability to withstand treatments, and shorter survival.
Canadian trial finds omega-3s help reduce cancer-related weight loss
Prior research indicates that fish oil supplements may help cancer patients maintain muscle (Colomer R et al. 2007).
To test the hypothesis, Vera Mazurak, Ph.D., of the University of Alberta in Edmonton, Canada, led a team that tested the effects of fish oil on weight, muscle, and fat in lung cancer patients.
The results of this small clinical trial, published in a journal of the American Cancer Society, indicate that fish oil may help combat cancer-related malnutrition (Murphy RA et al 2011).
The trial involved 16 patients who took fish oil daily – providing 2.5 grams of omega-3 EPA + DHA – and 24 patients who took no fish oil.
The study ran until patients completed their initial chemotherapy treatments, which lasted about 10 weeks.
Muscle and fat were periodically measured, blood was collected, and weight was recorded at the start of the study and throughout chemotherapy.
Patients receiving fish oil maintained their weight, but patients who did not take fish oil lost an average of 2.3 kilograms (five lbs.).
Sixty-nine percent of patients in the fish oil group gained or maintained muscle mass.
The patients with the greatest increase in their omega-3 blood levels following fish oil supplementation had the greatest gains in muscle.
Comparatively, only 29 percent of patients in the control group maintained muscle mass, and overall, patients in this group lost one kilogram of muscle.
The rate at which patients survived for one year tended to be greater in the fish oil group (60 percent vs. 38.7 percent).
No difference in total fat tissue was seen between the two groups, nor did fish oil seem to allow a higher dose of chemotherapy drugs to be used without increased adverse effects.
The authors concluded that two grams of fish oil per day provides a benefit over standard care, allowing patients to maintain their weight and muscle mass during chemotherapy.
“Fish oil may prevent loss of weight and muscle by interfering with some of the pathways that are altered in advanced cancer,” said Dr. Mazurak. “This holds great promise because currently there is no effective treatment for cancer-related malnutrition.”
Dr. Mazurak noted that fish oil is safe and non-toxic with virtually no side effects, and that it may be beneficial to patients with other forms of cancer and other chronic diseases that are associated with malnutrition, as well as to elderly individuals who are at risk for muscle loss.
  • Agency for Healthcare Research and Quality (AHRQ). Effects of Omega-3 Fatty Acids on Cancer. Evidence Report/Technology Assessment: Number 113. AHRQ Pub. No. 05-E010-1, February 2005. Accessed at http://www.ahrq.gov/clinic/epcsums/o3cansum.htm
  • Edwards IJ, O'Flaherty JT. Omega-3 Fatty Acids and PPARgamma in Cancer. PPAR Res. 2008;2008:358052.
  • Murphy RA et al. Supplementation with fish oil increases first-line chemotherapy efficacy in patients with advanced nonsmall cell lung cancer.CANCER; Published Online: February 28, 2011 (DOI: 10.1002/cncr.25709)
  • Boutros C, Somasundar P, Razzak A, Helton S, Espat NJ. Omega-3 fatty acids: investigations from cytokine regulation to pancreatic cancer gene suppression. Arch Surg. 2010 Jun;145(6):515-20. Review.
  • Colomer R, Moreno-Nogueira JM, García-Luna PP, García-Peris P, García-de-Lorenzo A, Zarazaga A, Quecedo L, del Llano J, Usán L, Casimiro C. N-3 fatty acids, cancer and cachexia: a systematic review of the literature. Br J Nutr. 2007 May;97(5):823-31. Review.
  • Fasano E, Serini S, Piccioni E, Innocenti I, Calviello G. Chemoprevention of lung pathologies by dietary n-3 polyunsaturated fatty acids. Curr Med Chem. 2010;17(29):3358-76. Review.
  • Murphy RA, Wilke MS, Perrine M, Pawlowicz M, Mourtzakis M, Lieffers JR, Maneshgar M, Bruera E, Clandinin MT, Baracos VE, Mazurak VC. Loss of adipose tissue and plasma phospholipids: relationship to survival in advanced cancer patients. Clin Nutr. 2010 Aug;29(4):482-7. Epub 2009 Dec 2.
  • Baracos VE, Mazurak VC, Ma DW. n-3 Polyunsaturated fatty acids throughout the cancer trajectory: influence on disease incidence, progression, response to therapy and cancer-associated cachexia. Nutr Res Rev. 2004 Dec;17(2):177-92.