Omega-3 Fatty Acids


Nancy Hepp, MS, BCCT Project Manager

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Laura Pole, RN, MSN, OCNS, BCCT Senior Researcher

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Last updated November 3, 2020.

Also known by these names

  • O3FAs
  • ω-3 fatty acids
  • n-3 fatty acids
  • omega 3s
  • Individual O3FAs:
    • Docosahexaenoic acid (DHA)
    • Eicosapentaenoic acid (EPA)
    • Alpha-linolenic acid (ALA)

Key Points

  • Before using this therapy, consult your oncology team about interactions with other treatments and therapies. Also make sure this therapy is safe for use with any other medical conditions you may have.
  • Omega-3 fatty acids are found naturally in many fish and a few seeds and walnuts.
  • Omega-3s are widely available as supplements.
  • BCCT is interested in omega-3s because evidence shows benefits in several types of cancer treatment, and preliminary evidence shows omega-3s may reduce risks of breast and colon cancer.
  • While omega-3s are generally considered safe, a few cautions and interactions are noted.

Omega-3 fatty acids are a type of polyunsaturated fatty acid (PUFA) found naturally in these foods and supplements:

Expand list

The three main omega-3 fatty acids are docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA) and alpha-linolenic acid (ALA). DHA and EPA generally show greater benefits in cancer, but are found only in animal sources. ALA from plant sources is converted to DHA and EPA in our bodies, but with a low conversion efficiency. ALA is not recommended as your sole source of omega-3s.2

Clinical Practice Guidelines

2013 evidence-based clinical practice guidelines from the American College of Chest Physicians recommended oral nutritional supplementation with omega-3 fatty acids to improve the nutritional status for lung cancer patients with sarcopenia (loss of muscle tissue).3

Treating the Cancer

Working against cancer growth or spread, improving survival, or working with other treatments or therapies to improve their anticancer action

Clinical Evidence

Breast Cancer

  • Improved outcomes with DHA added to chemotherapy in a small trial of metastatic breast cancer patients4

Colorectal Cancer

  • A diet rich in omega-3 fatty acids is associated with higher survival with colorectal cancer5
  • Reduced length of hospital stay, but no reduction in noninfectious complications or mortality when taken before surgery in a nutritional supplement also including arginine and nucleotides6
  • No decrease in tumor size or improvement in patient survival times in a 2015 review7
  • Reduced number and size of rectal adenomas8
  • Eicosapentaenoic acid (EPA) effects:
    • Improved overall survival in patients undergoing liver resection surgery for colorectal cancer liver metastases9
    • Reduced the extent of blood vessel networks consistent with reduced creation of new blood vessels to supply tumors (angiogenesis) with EPA use10
    • Compared with a placebo, eicosapentaenoic acid (EPA) either with or without aspirin did not reduce the proportion of patients with at least one colorectal adenoma in patients with sporadic colorectal neoplasia.11

Prostate Cancer

A group of men with prostate cancer combining omega 3 supplements with a low-fat (15 percent of calories from fat) diet for four to six weeks before prostatectomy was compared to a control group consuming the standard American diet with 40 percent of calories from fat and no fish oil supplementation. At prostatectomy, the group supplement had smaller prostates (both benign and malignant components), lower proliferation index, and plasma that inhibited growth of prostate cancer cells in vitro more than the plasma from the control patients.12 Other effects in prostate cancer:

  • Decreased prostate cancer proliferation and decreased prostate tissue omega-6:omega-3 ratios, but no change in serum insulin-like growth factor I (IGF-1) in a small study of men undergoing radical prostatectomy13

Conflicting interactions with chemotherapy have been reported:

  • No adverse side effects and possible improved anthracycline-based chemotherapy outcome were found in a small uncontrolled trial of group patients with rapidly progressing visceral metastases.14
  • Rise in plasma levels after supplementation in healthy volunteers to levels capable of causing chemoresistance to cisplatin in mice; use is not recommended on the days surrounding chemotherapy.15

Lab and Animal Evidence

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Managing Side Effects and Promoting Wellness

Managing or relieving side effects or symptoms, reducing treatment toxicity, supporting quality of life or promoting general well-being

Results related to patient body weight and composition:

  • Omega-3 fatty acid (EPA and DHA) capsules or supplements with EPA have been associated with weight stabilization, gain in lean body mass, and improvement in quality of life markers in patients losing weight as a result of advanced pancreatic and head and neck cancers.22
  • Promoted weight maintenance or gain during cancer treatment, and improved scores of physical function and global health status23
  • Maintained body weight during chemotherapy24
  • The weight of patients with gastrointestinal cancer (anal, colorectal, esophageal, stomach) increased significantly with EPA supplementation.25 EPA and DHA ameliorated muscle loss and myosteatosis (the presence of intermuscular and intramuscular adipose tissue) in clinical studies.26
  • In patients with colorectal cancer, EPA supplements increased weight and improved scores of health-related quality of life, with a trend toward fewer interruptions of chemotherapy treatment in a small study;27 EPA also increased mean weight and energy levels in an uncontrolled trial of colorectal cancer patients undergoing chemotherapy with folinic acid, 5-fluorouracil, irinotecan (FOLFIRI)28
  • A small study involving cancer patients receiving chemotherapy after surgical tumor (mainly gastrointestinal) removal found that fish oil supplementation reduced weight loss and improved the function of blood neutrophils.29
  • Omega-3 supplements improved outcomes, especially body composition, in patients undergoing chemotherapy and/or radiotherapy.30
  • EPA reduced deterioration of nutritional status resulting from antineoplastic therapies (therapies to block the formation of neoplasms) by improving calorie and protein intake31

High-dose EPA inhibited bone resorption in breast cancer survivors taking aromatase inhibitors.3233

Omega-3s reduced paclitaxel-induced peripheral neuropathy in a small clinical study of breast cancer patients.34 One review found reduced incidence of peripheral neuropathy,35 but another review found insufficient evidence yet exists to recommend use for treating or preventing chemotherapy-induced peripheral neuropathy (CIPN).36

Reduced postoperative infectious complications and hospital stay after colorectal cancer surgery in one study37 but no improvement in infectious or non-infectious postoperative complications in another3839

Dietary omega-3 fatty acids combined with guarana extract and a diet rich in whole foods, fruits and vegetables can treat cancer-related fatigue in patients with breast cancer.40

Nutritional supplementation with omega-3 fatty acids, arginine and nucleotides resulted in a marked improvement of immune functions in cancer patients undergoing surgery and a reduction in infectious complications, hospital stay and co-morbidities.41

Combination therapies:

  • Medroxyprogesterone or megestrol acetate, eicosapentaenoic acid (EPA), L-carnitine and thalidomide
    • Increased lean-body mass, decreased resting energy expenditure, improved fatigue and appetite, improved performance status in patients with cachexia (weakness and wasting)42
  • Omega-3 fatty acid and microbial cell preparation

Reducing Risk

Reducing the risk of developing cancer or the risk of recurrence

Clinical Evidence

Substantial data support the importance of omega-3 fatty acids for colorectal cancer prevention.44 A decreased risk of colon cancer with fish oil supplements, primarily in men, was found in one study; an increased risk was found with individuals with high genetic risk.45 Eicosapentaenoic acid (EPA) alone reduced the number and size of polyps in patients with familial adenomatous polyposis.46 Eicosapentaenoic acid (EPA) alone, either with or without aspirin, did not reduce the proportion of patients with sporadic colorectal neoplasia who had at least one colorectal adenoma, but did reduce the number of adenomas.47

Higher omega-6 to omega-3 ratios are associated with higher risk of breast cancer,48 while higher consumption of dietary marine omega-3 polyunsaturated fatty acids is associated with a lower risk of breast cancer.49 Higher levels from combined diet and supplements are associated with reduced risks of breast cancer.50 No impact of supplements on breast cancer recurrence and improved overall mortality in patients were found with early stage breast cancer, but marine omega-3s from food were associated with reduced risk of additional breast cancer events and all-cause mortality.51

Higher levels from combined diet and supplements are associated with reduced risks of breast cancer.52 No impact of supplements was found on breast cancer recurrence and improved overall mortality in patients with early stage breast cancer, but marine omega-3s (DHA and EPA) from food were associated with reduced risk of additional breast cancer events and all-cause mortality.53

Data on omega-3 fatty acid supplementation for prostate cancer prevention are inconclusive. A 2017 review of the literature showed no clear relationship between fish-derived omega-3 fatty acids and risk of prostate cancer,54 but a separate review found that consumption of omega-3 long-chain polyunsaturated fatty acids (LCPUFAs) and "an omega-6/omega-3 ratio of 2-4:1 are associated with a reduced risk of breast, prostate, colon and renal cancers."55

Lab and Animal Evidence

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Optimizing Your Terrain

Creating an environment within your body that does not support cancer development, growth or spread

  • Reduced inflammation,57 or improved anti-inflammatory markers58
  • 59 including when accompanying anticancer treatment60 and in patients undergoing radical colorectal cancer resection61


A few cautions are noted. Please see the Memorial Sloan Kettering Cancer Center’s About Herbs website for information.

  • High blood concentrations of omega-3s are associated with increased risk of prostate cancer (see the Foundation for Alternative and Integrative Medicine for an analysis of the study that found this).
  • Increased resistance to chemotherapy is a concern;62 a type of omega-3 fatty acid, 16:4(n-3), can reduce the activity of the chemotherapy drug cisplatin. Use is not recommended on the days surrounding chemotherapy.6364
  • 2018 review conclusions:65
    • Four grams of supplementation may impair clotting; patients may want to eliminate omega-3 supplements before and immediately after surgery.
    • A few adverse reactions and interactions with prescription and other drugs have been observed.


BCCT does not recommend therapies or doses, but only provides information for patients and providers to consider as part of a complete treatment plan. Patients should discuss therapies with their physicians, as contraindications, interactions and side effects must be evaluated. Levels of active ingredients of natural products can vary widely between and even within products. See Quality and Sources of Herbs, Supplements and Other Natural Products.

Dosage recommendations are available from these sources:

Integrative Programs, Protocols and Medical Systems

For more information about programs and protocols, see our Integrative Programs and Protocols page.

Non-cancer Uses of Omega-3 Fatty Acids

BCCT has not reviewed the effectiveness of this therapy for non-cancer uses.

  • Depression
  • High cholesterol
  • Cardiovascular risk factors, including elevated triglyceride levels
  • Stroke
  • Rheumatoid arthritis
  • NSAID-associated gastroduodenal damage
  • Sunburn and sensitivity to ultraviolet radiation
  • Cystic fibrosis
  • Systemic lupus erythematosus (SLE)
  • Type 1 diabetes

Note: BCCT has not conducted an independent review of research of Omega-3 fatty acids. This summary draws from the Memorial Sloan Kettering Cancer Center’s About Herbs and other sources as noted.

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