Updated: Apr 18, 2020
By Wageningen Beasts
You might have heard about it quite often: fish oil. A lot of online experts claim fish oil is good for you. There are countless claimed effects of fish oil supplementation on health. Three examples of such claims are that fish oil is good for the immune system, it relieves depression and protects against cardiovascular disease. The question arises which claims have proven to be true, if any are true at all. Should we take these smelly rascals? In short: ‘fish oil: yay or nay?’.
What is fish oil? Fish oil supplements consist of omega-3 fatty acids, which are polyunsaturated fatty acids (PUFAs). An unsaturated fatty acid has a double bond between two carbon atoms. The picture below shows the difference between saturated and unsaturated fatty acids. The ‘-‘ sign between two C’s (carbon atoms) means a single bond, and ‘=’ means a double bond. You can see that the saturated fatty acids are straight and stiff: they cannot bend. The unsaturated fatty acids are more flexible, since the double bond allows them to have a more bended structure. This bent structure is more healthy, as a straight structure is thought to pile up more easily in the blood vessel wall and thereby cause atherosclerosis (clogging of the arteries due to fat accumulation). This explains why unsaturated fatty acids are more healthy than saturated fatty acids.
Mono unsaturated fatty acids (MUFAs) have a single double bond and PUFAs have multiple double bonds, which increases the ability to bend even more, making PUFAs even healthier than MUFAs. Fats that contain unsaturated fatty acids have a lower melting point than saturated fatty acids. This explains why fats that consist mostly of unsaturated fatty acids (like most plant oils) are liquid at room temperature, while fats made out of saturated fatty acids (most animal-derived fats, like butter) are solid at room temperature. Fish oil is liquid at room temperature, which shows that it consists of unsaturated fatty acids. Just a fun fact. Another fun fact: these differences in boiling points explain why oil smokes when being heated for too long during cooking, while butter does not.
For those who know little of chemistry, don’t worry. The chemistry part is over, and if you did not understand it, that doesn’t matter in order to understand the rest of the story.
Omega-3 fatty acids are essential fatty acids. They are essential because the body cannot produce them, which is why they have to be obtained from the diet. There are three types of omega-3 fatty acids which are of importance for humans: α-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). ALA is derived from plant sources and can thus be found in foods such as nuts, seeds and seed oils. EPA and DHA are mainly present in fish and fish oils. Thus, when taking fish oil supplements, you ingest EPA and DHA.
What are the health effects of fish oil? Omega-3 fatty acids, mainly EPA and DHA, have been linked to numerous health effects. There are a lot of health claims regarding the intake of these fatty acids, but they are not all true. The EFSA has extensively reviewed this and came to the conclusion that the intake of fish oil (supplements) has the following health effects:
EPA and DHA contribute to maintenance of the normal function of the heart (reduced heart rate and reduced risk of arrhythmia(=irregular heartbeats)). This effect already takes place with a daily intake of 250 mg.
EPA and DHA are able to lower blood pressure. Blood pressure plays an important role in cardiovascular disease (CVD). Thereby, EPA and DHA decrease the risk of CVD. This effect takes place with a daily intake of 750 mg.
EPA and DHA contribute to the maintenance of normal (=low) (fasting) blood concentrations of triglycerides (one glycerol attached to three fatty acids, in other words: fat), which means that they lower triglyceride levels. The levels of triglycerides (fats) in the blood are a (general) health marker. Having normal (low) blood concentrations of triglycerides lowers the risk of getting CVD. This effect takes place with a daily intake of 2 g.
EPA and DHA can decrease thrombosis by functioning as blood thinners. This lowers the risk of stroke. This effect takes place with a daily intake of more than 4 g, which is considered to be very high.
There might be several other health effects, but there is not enough evidence to support these claims.
In summary, up till now scientific evidence is only conclusive about the decreased risk of CVD with supplementation of fish oil, which is nonetheless a great health effect.
Conclusion – Fish oil: Yay or nay?
How much and which supplements should I take? As said before, omega-3 supplementation can result in several health benefits. Different daily dosages are required in order to obtain these health effects. These values range from 250 mg per day to above 4 g per day. However, like any other nutrient: more is never better. There is an optimal intake, but if you exceed this intake, it might give adverse health effects. This is because a lot of fatty acids are made from other fatty acids in the body. This happens in an optimal ratio of EPA/DHA to other fatty acids. If you ingest too much EPA/DHA, the ratio between EPA and DHA gets out of balance. The FDA states that it is safe to consume up to 3000 mg of omega-3 per day, and the EFSA showed that supplementation of 5 grams of EPA and DHA is still safe.
Alternatively, these high daily intakes can be achieved by fish consumption. However, one would have to eat a lot of fish to get the same levels as taking fish oil capsules. Omega 3 is most abundant in mackerel, salmon, herring and tuna, which, if consumed fresh, contain around 1000-1500 mg of omega-3 fatty acids per 100 grams. Canned fish already contains less omega-3. Also, when fish is canned in oil, some of the omega-3 fatty acids might leak into the oil. If you discard the oil, you lose omega-3 fatty acids. Fish that is canned in water does not show this problem.
Here is a table that shows the omega-3 content of several types of fish: http://www.seafoodhealthfacts.org/seafood-nutrition/healthcare-professionals/omega-3-content-frequently-consumed-seafood-products
If you look at the table, you can imagine that you have to eat fish almost daily to get the same levels of intake as when you take fish oil supplements. Of course, eating fish is highly recommended over taking supplements, as foods contain many more substances that can be healthy compared to supplements.
The average fish oil supplement has 1000 mg of fish oil per capsule, which contains approximately 550 mg of EPA/DHA. I would personally recommend to have a daily intake of 3 grams of fish oil, based on the health effects and the safety. Fish oil supplements are widely available, and have several brands. More expensive brands do not necessarily are of better quality than cheaper brands. However, there are some brands that make supplements according to the Current Good Manufacturing Practices (CGMP) of the Food and Drug Administration (FDA), meaning that these brands are trustworthy and are assured of good quality. Two of such brands are NOW and Solgar.
Last side note: There is one situation in which you should not take fish oil supplements, namely for cancer patients undergoing chemotherapy treatment. The fish oil can interfere with the chemotherapy, making the therapy possibly less effective. Thus, for cancer patients taking fish oil supplements is generally advised against. Also, when you have a blood pressure that is too low, fish oil supplements might not be a good idea as these lower blood pressure (even though this effect is small). If you have any doubts whether you should use fish oil supplements or not in a certain case, just ask your doctor!
 Whitney, E., & Rolfes, S. R. (2007). Understanding nutrition. Cengage Learning.  EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA); Scientific Opinion on the substantiation of health claims related to eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), docosapentaenoic acid (DPA) and maintenance of normal cardiac function (ID 504, 506, 516, 527, 538, 703, 1128, 1317, 1324, 1325), maintenance of normal blood glucose concentrations (ID 566), maintenance of normal blood pressure (ID 506, 516, 703, 1317, 1324), maintenance of normal blood HDL-cholesterol concentrations (ID 506), maintenance of normal (fasting) blood concentrations of triglycerides (ID 506, 527, 538, 1317, 1324, 1325), maintenance of normal blood LDL-cholesterol concentrations (ID 527, 538, 1317, 1325, 4689), protection of the skin from photo-oxidative (UV-induced) damage (ID 530), improved absorption of EPA and DHA (ID 522, 523), contribution to the normal function of the immune system by decreasing the levels of eicosanoids, arachidonic acid-derived mediators and pro-inflammatory cytokines (ID 520, 2914), and “immunomodulating agent” (4690) pursuant to Article 13(1) of Regulation (EC) No 1924/2006. EFSA Journal 2010;8(10):1796. [32 pp.]. doi:10.2903/j.efsa.2010.1796. Available online: www.efsa.europa.eu/efsajournal.htm  Mozaffarian, D., & Wu, J. H. (2011). Omega-3 fatty acids and cardiovascular disease: effects on risk factors, molecular pathways, and clinical events. Journal of the American College of Cardiology, 58(20), 2047-2067.  US Food and Drug Administration. (2004). FDA announces qualified health claims for omega-3 fatty acids. US Department of Health and Human Services.  Agostoni, C., Bresson, J. L., Fairweather-Tait, S., Flynn, A., Golly, I., Korhonen, H., … & Neuhäuser-Berthold, M. (2012). Scientific opinion on the tolerable upper intake level of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and docosapentaenoic acid (DPA). EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA), Parma, Italy.