Fish Oil: Frequently Asked Questions

What will fish oil do for me?
Fish oil is an excellent source of omega-3 fatty acids, specifically eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). EPA is an important signaling molecule in the biochemical pathways related to growth and inflammation, and DHA a primary structural component of the brain, skin, and sperm. In general, it is important to consume a low ratio of omega-6 to omega-3 fatty acids (i.e., 1:1 or 2:1). However, with the current state of food availability and common eating practices, Americans tend to consume an omega-6 to omega-3 ratio of 10:1 or 20:1 (summarized in [1]). Fish oil supplements can help bolster your omega-3 intake and reduce your omega-6 to omega-3 ratio.
Omega-3 fatty acids, fish, and fish oil have been shown to prevent heart disease (e.g., [2-4]), though some studies have concluded that there is no benefit [5]. Fish oil may also be particularly beneficial for athletes, as supplementation has been shown to promote healing at sites of injury [6], reduce muscle soreness from eccentric bicep curls [7], reduce heart rate and oxygen consumption during cycling [8], improve pulmonary function during wrestling [9], and reduce the severity of exercise-induced bronchoconstriction in elite triathletes and runners [10]. Indeed, athletes who are pushing themselves to their bodies’ limits may be able to increase their potential by consuming a healthy diet rich in omega-3 fatty acids.
Do fish oil supplements contain mercury?
Two independent studies: one peer-reviewed research article [11] and one study by Consumer Reports [12] showed that fish oil supplements do not contain dangerous amounts of mercury.
Do fish oil supplements contain other contaminants, such as pesticides?
Fish oil supplements might be contaminated with persistent organic pollutants (POPs), which are environmental contaminants that accumulate in fish. The level of POPs varies depending on the type of fish, the geographic region from which the fish came, whether the fish was farmed (contains less POPs) or caught from the wild, the year, and the methods of processing [13-15]. Indeed, the health benefits of fish and fish oil can be diminished with high exposure to POPs, as highlighted in a recent study published in May of 2015 [16]. Consumer Reports [12] evaluated 15 top-selling fish oil brands for a specific POP: polychlorinated biphenyls (PCBs). They found that none contained more than the limit set by the US Pharmacopeia (USP), though several contained enough to require a warning label under California’s Proposition 65, a consumer right-to-know law.
Should I worry about my fish oil going bad?
Yes, fish oil is very susceptible to auto-oxidation, when the fatty acids break down and even turn into pro-oxidants (i.e., peroxides), which are the opposite of antioxidants. To prevent oxidation, store fish oil in the freezer, prevent exposure to high temperatures, and look for supplements that contain antioxidants (e.g., vitamin E, vitamin C) [17]. Krill oil, another marine omega-3 fatty acid source, naturally contains astaxanthin, a potent antioxidant that may provide antioxidant benefits beyond keeping the omega-3 fatty acids fresh [18,19].
I prefer to get my nutrients from “real food” rather than supplements. Would it be better for me to eat more tuna and salmon than to take fish oil?
In general, fish is recommended over fish oil because fish is a good source of protein, vitamin D, vitamin A, calcium, and other beneficial nutrients. The American Heart Association (AHA) recommends at least two 3.5 oz. fish meals per week with fish high in omega-3 fatty acids [20]. However, use caution in selecting the source of fish to maximize nutrients and minimize contaminants [4,21,22]. Because of the large amount of anabolism and crucial development that occurs in utero, there has been much effort to optimize fish and fish oil recommendations for pregnant women (see [21]). These recommendations apply to most healthy people.
Salmon, pollock, and squid are the best choices. Salmon is low in mercury and high in omega-3s (2 μg mercury and 1200-2400 mg omega-3s per 4 oz serving [21]) while pollock contains 6 μg mercury and 600 mg omega-3s per 4 oz serving (pollock is a common fish used in fish sticks and fish from restaurants). Bad choices of fish include shark and swordfish, which have approximately 150 μg mercury and 1000-1250 mg omega-3’s per 4 oz serving [21]. Albacore tuna is moderately high in mercury (40 g mercury and 1000 mg omega-3’s per 4 oz), and therefore it is not recommended to consume more than 6 oz of albacore tuna per week [21].
When should I take fish oil?
In order to stimulate digestive enzymes and ensure that all of the omega-3 fatty acids are being absorbed in the small intestine, consume fish oil with food.
How much fish oil should I take?
The AHA recommends that persons without documented heart disease consume at least 2 fish meals per week. For individuals with heart disease, the AHA recommends about 1 g of EPA + DHA per day, with a larger dose of 2-4 g EPA + DHA per day for those who need to lower blood triglycerides and are under a physician’s care [20]. The US Food and Drug Administration (FDA) recommends a maximum of 3 g omega-3 fatty acids per day with a maximum of 2 g from supplements [23]. Larger doses can increase the risk of uncontrolled bleeding [4]. It is important to determine the dose of EPA + DHA from the label of a fish oil supplement, rather than simply looking at the grams of fish oil, because there are other fatty acids besides EPA and DHA in fish oil. Finally, while some people might prefer using krill oil vs. fish oil, the dosage of omega-3 fatty acids in krill oil is considerably lower than in fish oil, requiring higher doses (and more expense) to get an equivalent dose of EPA + DHA.

  1. Simopoulos AP. Omega-3 fatty acids and athletics. Curr. Sports Med. Rep. 2007;6:230-6.
  2. Wang C, Harris WS, Chung M, Lichtenstein AH, Balk EM, Kupelnick B, et al. n-3 Fatty acids from fish or fish-oil supplements, but not α-linolenic acid, benefit cardiovascular disease outcomes in primary- and secondary-prevention studies: a systematic review. Am. J. Clin. Nutr. 2006;84:5-17.
  3. Delgado-Lista J, Perez-Martinez P, Lopez-Miranda J, Perez-Jimenez F. Long chain omega-3 fatty acids and cardiovascular disease: a systematic review. Br. J. Nutr. 2012;107:S201-13.
  4. Kris-Etherton PM, Harris WS, Appel LJ. Fish consumption, fish oil, omega-3 fatty acids, and cardiovascular disease. Circulation. 2002;106:2747-57.
  5. Rizos EC, Ntzani EE, Bika E, Kostapanos MS, Elisaf MS. Association between omega-3 fatty acid supplementation and risk of major cardiovascular disease events: A systematic review and meta-analysis. J. Am. Med. Assoc. 2012;308:1024-33.
  6. Kiecolt-Glaser JK, Glaser R, Christian LM. Omega-3 Fatty Acids and Stress-Induced Immune Dysregulation: Implications for Wound Healing. Mil. Med. 2014;179:129-33.
  7. Jouris KB, Mcdaniel JL, Weiss EP. The effect of omega-3 fatty acid supplementation on the inflammatory response to eccentric strength exercise. J. Sport. Sci. Med. 2011;10:432-8.
  8. Peoples GE, McLennan PL, Howe PRC, Groeller H. Fish oil reduces heart rate and oxygen consumption during exercise. J. Cardiovasc. Pharmacol. 2008;52:540-7.
  9. Tartibian B, Maleki BH, Abbasi A. The effects of omega-3 supplementation on pulmonary function of young wrestlers during intensive training. J. Sci. Med. Sport. Sports Medicine Australia; 2010;13:281-6.
  10. Mickleborough TD, Murray RL, Ionescu AA, Lindley MR. Fish oil supplementation reduces severity of exercise-induced bronchoconstriction in elite athletes. Am. J. Respir. Crit. Care Med. 2003;168:1181-9.
  11. Foran SE, Flood JG, Lewandrowski KB. Measurement of Mercury Levels in Concentrated over-the-Counter Fish Oil Preparations: Is Fish Oil Healthier than Fish? Arch. Pathol. Lab. Med. 2003;127:1603-5.
  12. Fish-oil pills vs. claims. Consum. Reports Mag. 2012 Jan;
  13. Ruzzin J, Jacobs DR. The secret story of fish: decreasing nutritional value due to pollution? Br. J. Nutr. 2012;108:397-9.
  14. Turyk ME, Bhavsar SP, Bowerman W, Boysen E, Clark M, Diamond M, et al. Risks and benefits of consumption of great lakes fish. Environ. Health Perspect. 2012;120:11-8.
  15. Simmons AL, Schlezinger JJ, Corkey BE. What are we putting in our food that is making us fat? Food additives, contaminants, and other putative contributors to obesity. Curr. Obes. Rep. 2014;3:273-85.
  16. Hong MY, Lumibao J, Mistry P, Saleh R, Hoh E. Fish oil contaminated with persistent organic pollutants reduces antioxidant capacity and induces oxidative stress without affecting its capacity to lower lipid concentrations and systemic inflammation in rats. J. Nutr. 2015;145:939-44.
  17. Wang H, Liu F, Yang L, Zu Y, Wang H, Qu S, et al. Oxidative stability of fish oil supplemented with carnosic acid compared with synthetic antioxidants during long-term storage. Food Chem. Elsevier Ltd; 2011;128:93-9.
  18. Ulven SM, Kirkhus B, Lamglait A, Basu S, Elind E, Haider T, et al. Metabolic effects of krill oil are essentially similar to those of fish oil but at lower dose of EPA and DHA, in healthy volunteers. Lipids. 2011;46:37-46.
  19. Ramprasath VR, Eyal I, Zchut S, Jones PJH. Enhanced increase of omega-3 index in healthy individuals with response to 4-week n-3 fatty acid supplementation from krill oil versus fish oil. Lipids Health Dis. 2013;12:178.
  20. The American Heart Association. Fish 101 [Internet]. 2015 [cited 2015 May 28]. Available from:
  21. Wenstrom KD. The FDA’s new advice on fish: it’s complicated. Am. J. Obstet. Gynecol. Mosby, Inc; 2014;211:475-8.e1.
  22. Chowdhury R, Stevens S, Gorman D, Pan A, Warnakula S, Chowdhury S, et al. Association between fish consumption, long chain omega 3 fatty acids, and risk of cerebrovascular disease: systematic review and meta-analysis. BMJ. 2012;345:e6698.
  23. Food and Drug Administration. FDA Announces Qualified Health Claims for Omega-3 Fatty Acids. 2004.
Google Tracking Google Plus Tracking Twitter Tracking