The truth about Fish Oil

Many cupboards across the country are home to a little tub of those squishy yellow fish oil pills.

Over the last decade or so, fish oil capsules have become exceptionally popular and now take pride of place on any health supplement shop shelf.

Eating fish is  generally considered healthy. Fish, in general, is low in saturated fats and less calorific than red meats. Populations that consume large amounts of fish also have lower incidence of heart disease. Additionally, high consumption of red meat has been linked with increased risk of bowel cancer (1) – further promoting the eating of fish is therefore good for public health.

The idea for a long time has been that the oils and fats in fish is what really sets it apart from other meat products – hence why we now see fish oil supplements.

But what is the truth about eating fish oils regularly? Will you really be ‘healthier’? Are fish oils protective against heart disease for example?

Lets find out…but first a bit of background about what fish oils actually are.



What are ‘Fish Oils’?


Fish oil is simply an oily substance derived from the tissues of ‘oily’ fish. The most oily fish are sardines, mackerel, salmon, halibut and tuna. Lots of other fish also contain these oils but to a lesser degree (2).


 The major components of fish oil are the omega-3 fatty acids:


Eicosapentaenoic acid (EPA)

Docosahexaenoic acid (DHA)


An additional type of fatty acid is also important in human health but found in nuts, not oily fish:


α-linolenic acid (ALA)

.Both EPA and DHA are described as ‘essential’ – we have to obtain these fatty acids from our diets, we cannot make them ourselves (3). ‘Fatty’ fish such as salmon and sardines are great sources of both of these compounds. If you aren’t a fan of fish, flax seeds, pumpkin seeds and walnuts are just a few other dietary sources from which you can obtain high levels of EPA and DHA.


A handy conversion schematic from Dr. Ben King at


Omega-3 fatty acids are important for normal metabolic function and are especially important for growth in infants (4). DHA is found in large quantities in the brain where it acts as a major structural component (5).  Aside from structural function, DHA and EPA are thought to play an important role in brain health – good evidence suggest omega-3s are important in maintaining mood stability and show potential in combating depression (discussed more below).


As with a lot of popular supplements – many remarkable health benefits have been attributed to omega-3s and the broader term of ‘fish oils’. As always, as I have shown you before, when we dig deeper we see that many common claims about supplements either exaggerate the truth or are entirely made up. Some supplements have very weak literature and research behind them, fish oils however have been researched in depth for a number of years so we can draw firmer conclusions regarding their therapeutic efficacy.



Are there health benefits: What does the science say?


At some point or another, fish oils have been said to cure or alleviate an extremely wide range of maladies and diseases. I won’t cover them all here as the list is practically endless and mostly made up. Instead I will focus on common diseases and pathologies which have the most research behind them concerning fish oils as a therapeutic supplements.


.Cardiovascular Disease


CVD and fish oils go hand in hand. Aside from widely cited ‘mental boosting’ effects, the next benefit on the list of fish oil supplements is almost almost cardiovascular health. We know that dietary fat intake is very important for cardiovascular health and can be a major indicator of risk of heart attack. In general, we know that trans fats are especially bad when it comes to heart health and that polyunsaturated fats are a much better choice and may even be protective against heart disease if eaten in moderation (6). It therefore makes sense that so much research has investigated the effects of omega-3 fatty acids and CV health and disease risk.


Basic anatomy of the heart – many of these components can be adversely affected by cardiovascular disease



Most of that research sends a clear message: Fish oil supplements do not protect against heart attacks of strokes. Although some individual papers have shown potential benefit – i.e. two papers from 1999 and 2009 (7,8) suggesting fish oils may have beneficial effects on certain abnormal heart rhythms. However, since then meta studies have refuted that specific claim (9) and also gone on to conclude that…


”Omega-3 Fatty Acid supplementation did not reduce the chance of death, cardiac death, heart attack or stroke”


This is the conclusion of a 2012 meta-study (Journal of the American Medical Association) which analysed the data from 20 separate studies and well over 60,000 patients (10). This is a good amount of data so we can be confident in this conclusion as it stands.

It is important to note that although fish oil doesn’t seem to prevent death from heart attacks of stroke it does appear to have beneficial effects for previous sufferers of heart attacks and other people with a history of cardiovascular disease. Omega-3s possess modest anti-inflammatory properties (11) and it is probably because of this that a cohort of heart attack survivors that received daily fish oil supplements for 6 months showed improved heart function overall and lower markers of systemic inflammation than their control counterparts (12). Furthermore, omega-3 fatty acid supplementation greater than one gram a day for at least a year may be protective against cardiac death, sudden death, and myocardial infarction in people who have a history of cardiovascular disease.

Another meta study also concluded that there was ‘tentative’ evidence of an anti-inflammatory effect  from fish oil supplementation. More data will be needed to take a stronger position on this in the future.

Although not directly heart protective in healthy individuals the current evidence suggests fish oil supplements may benefit those who have a history of heart disease and/or have suffered a heart attack.


Prostate Cancer


I’ve decided to mainly write about prostate cancer here as this is the type of cancer with the most relevant studies. Omega-3s are often touted as having a strong anti-cancer effect but as I have said before: Just because a compound kills or inhibits the growth of cancer cells in vitro (in a cell culture dish) does not mean it qualifies as a cancer therapy by itself.


More true advice has never been given


Some studies have shown that fish oils rich in Omega-3s do inhibit tumour cell growth in vitro. This effect was deemed strong enough to suggest that a diet rich in Omega-3 fatty acids be used alongside traditional breast cancer treatments (13) – this may actually prove beneficial (this does not endorse Omega-3 fatty acids as a treatment by itself in any way).

But what about studies where they gave actual patients with cancer Omega-3 supplements or looked directly at Omega-3 blood concentrations? This has been mostly done with prostate cancer patients.

The area remains controversial due to the publication of a few papers with conflicting results.

One paper demonstrated that increased DHA in the blood was associated with a reduction in prostate cancer risk (14). However, two other papers have shown almost the exact opposite. One group showed that increased levels of DHA and EPA was associated with an increased risk of more aggressive prostate cancer (15).  Another group presented evidence that suggested a link between high blood levels of omega -3 fatty acids and an increased risk of prostate cancer (16).

These papers have all been published in the last few years, starting in 2012, so this is a an actively contested research  topic that has yet to see a solid consensus emerge. As such we can say that overall, given the available data, the effects of omega-3 supplementation on cancer, including prostate cancer, is currently inconclusive. 


Alzheimer’s Disease


It is unlikely that dietary intervention will prevent Alzheimer’s and even more unlikely that symptoms will be reversed once they manifest. A 2012 Cochrane meta-analysis (17) pooled the data from studies when individuals over the age of 60 had been given fish oils as a supplement. They found that taking fish oil supplements did not provide protection against the development of Alzheimer’s in the over 60s.


In their words…

“Our analysis suggests that there is currently no evidence that omega-3 fatty acid supplements provide a benefit for memory or concentration in later life”.


It is important to note that this meta-study specifically looked at those over the age of 60 as Alzheimer’s is typically a disease of old age. This study is therefore limited in a number of ways. It cannot tell us whether fish oil supplementation in younger years may ultimately prove protective against Alzheimer’s in old age. Although this remains unlikely, fatty acids are important brain components and do play a role in mood and brain function so there may be an as of yet, undiscovered link.


Mental Health


Overall, studies and meta-studies in this area have expressed the need for many more randomised controlled studies in order to increase the data pool and that the data is, in general, limited. The major review that suggested this need for more data also showed that omega-3s were an effective adjunctive therapy for depressive (but not manic) symptoms in bipolar disorder (18).


The most recent meta-study in this area from 2014, an analysis of 11 studies, looked at treating depression in patients diagnosed with Major Depressive Disorder (MDD) and those with depression but without a diagnosis of MDD.


They concluded…

‘The use of omega-3 PUFA is effective in patients with diagnosis of MDD and on depressive patients without diagnosis of MDD.”

Omega 3 fish oil supplements appear to be effective in treating depression. More data more establish this more strongly in the future.


Hypertension (High Blood Pressure)

Omega-3s may have a small beneficial effect on hypertension by lowering blood pressure (19). The effect currently shown in studies is small and appears to only effect individuals with hypertension. Studies which failed to replicate the blood pressure reduction may be due to dosage issues. Additionally, DHA and EPA don’t seem to have the same efficacy with DHA having potentially greater effects.

This area is worth exploring in greater detail with more data before a solid conclusion can be drawn.



Are there any dangers associated with fish oil supplements?


A 2013 review on fish oil supplement dangers concluded…

”appear mild at worst and are unlikely to be of clinical significance”

This is true of eating fish in general…not just taking fish oil supplements.



Heavy metal accumulation can be a problem with fish and predatory fish at the top of the food chain have higher levels of mercury due  to bio-accumulation over time. Mercury levels can range from very low to worryingly high in a single serving of fish. Usually from 10 ppb (parts per billion) of mercury all the way up to 1,000 (20). Luckily your average fish oil supplement contains 2 ppb mercury- well within tolerable limits (21).



The process of bio-accumulation means large predatory fish have greater levels of environmental toxins in their system than smaller prey fish. Original image from


Dioxins and dioxin like chemicals

Chronic exposure to low levels of dioxins may be carcinogenic and the chemical is classified as a human carcinogen (22).  There is also evidence that uterine exposure to dioxins leads to subtle developmental issues in children. In a similar fashion to mercury, chemicals like dioxin bio accumulate in fish so that the concentrations in the fish are much greater than the surrounding environment. In reputable brands of  fish oil supplements, dioxins will not be found. Always buy your supplements from reputable brands and suppliers.


Vitamin A

The liver and liver products of fish (i.e. cod liver oil) contain omega-3, but also the active form of vitamin A.

High intake of vitamin A can lead to dangerous Hypervitaminosis A.

I have covered the role of vitamins in health extensively here.


% Recommended Daily Allowances

FDA guidelines state that it is  safe to take up to 3000 mg of omega-3 per day. However, that is pure omega-3 oil not 3000 mg of fish oil.

Fish oil contain varying levels of omega-3 which should be labelled clearly on the back of the packaging.

A typical 1000 mg fish oil pill contains about 200-400 mg of omega-3 fatty acids. You would have to take over ten pills a day to be over recommended allowances – no chance of that.

.Ultimately taking fish oil supplements from a reputable producer and seller is no more dangerous than consuming fish frequently.



The Final Word


Dissecting out exactly what certain molecules and compounds are doing in the body is always tricky. This is certainly true of supplements. There is no doubt that supplements are a great idea for those deficient in a particular nutrient but the benefits of taking more of a particular nutrient when you are already meeting requirements are much harder to determine. This is a common theme running through supplement use in general.

Overall fish oils (Omega-3s) are physiologically important and play a number of key roles in the body. The science suggests that  supplementing with fish oils is no where near as ‘powerful’ as some manufactures would have you believe…

Currently the data suggests there is no clear protective effect against…

Risk of cancer

Risk of stroke

Risk of heart attack

Development of Alzheimer’s Disease


However! There is some evidence that Omega-3s are effective in…


Treating certain types or depression – more data would be ideal

Increasing general heart function following a heart attack

General reduction in markers of  systemic inflammation

May have small beneficial effects on hypertension

Although there are some minor risk associated with high fish oil intake (potential heavy metal ingestion), this risk is no greater than when simply eating fish. On this topic, researchers at Harvard’s School of Public Health said…


 ”The benefits of fish intake generally far outweigh the potential risks.”


I myself really enjoy eating fish – mainly salmon and tuna. I also eat mixed nuts frequently which include walnuts. All good sources of Omega-3 fatty acids. I also always have a tub of fish oil capsules handy at home. I do not take them every day but if I haven’t got hold of fresh fish for a week or two I will go ahead and supplement for a few days with capsules.


If you fancy doing the same, grab them for cheap down below. Also, check out the Microalgae Capsules – the vegetarian alternative to fish oil capsules.




Thanks for reading!






  1. Zhu, H; et al. (2013). “Red and processed meat intake is associated with higher gastric cancer risk: a meta-analysis of epidemiological observational studies.”. PLOS ONE. 8 (8)
  2. Kris-Etherton, Penny M.; William S. Harris, Lawrence J. Appel (2002). “Fish Consumption, Fish Oil, Omega-3 Fatty Acids, and Cardiovascular Disease”. Circulation. 106 (21): 2747–57.
  3. Moghadasian, Mohammed H. (2008). “Advances in Dietary Enrichment with N-3 Fatty Acids”. Critical Reviews in Food Science and Nutrition. 48 (5): 402–10.
  4. Freemantle E, Vandal M, Tremblay-Mercier J, Tremblay S, Blachère JC, Bégin ME, Brenna JT, Windust A, Cunnane SC (2006). “Omega-3 fatty acids, energy substrates, and brain function during aging”. Prostaglandins, Leukotrienes and Essential Fatty Acids. 75 (3): 213–20.
  5. “Nutrition for the Brain” (PDF)/DHA in Brain and Retina Structure” (PDF)
  6. Zaloga GP, Harvey KA, Stillwell W, Siddiqui R (2006). “Trans Fatty Acids and Coronary Heart Disease”. Nutrition in Clinical Practice. 21 (5): 505–512.
  7. Charnock John S (1999). “The role of omega-3 polyunsaturated fatty acid-enriched diets in the prevention of ventricular fibrillation” Asia Pacific Journal of Clinical Nutrition. 8 (3): 226–30.
  8. Li GR, Sun HY, Zhang XH, Cheng LC, Chiu SW, Tse HF, Lau CP (2009). “Omega-3 polyunsaturated fatty acids inhibit transient outward and ultra-rapid delayed rectifier K+currents and Na+current in human atrial myocytes”. Cardiovasc Res. 81 (2): 286–93.
  9. Khawaja, Owais; Gaziano, J. Michael; Djoussé, Luc (2012-02-01). “A meta-analysis of omega-3 fatty acids and incidence of atrial fibrillation”. Journal of the American College of Nutrition. 31 (1): 4–13.
  10. Rizos, E. C.; Ntzani, E. E.; Bika, E; Kostapanos, MS; Elisaf, MS (2012). “Association Between Omega-3 Fatty Acid Supplementation and Risk of Major Cardiovascular Disease Events: A Systematic Review and Meta-analysis”. Journal of the American Medical Association. 308 (10): 1024–33.
  11. Wall R, Ross RP, Fitzgerald GF, Stanton C (2010). “Fatty acids from fish: the anti-inflammatory potential of long-chain omega-3 fatty acids”. Nutr Rev. 68 (5): 280–89.
  12. Heydari B, Abdullah S (2016) Effect of Omega-3 Acid Ethyl Esters on Left Ventricular Remodelling After Acute Myocardial Infarction: The OMEGA-REMODEL Randomised Clinical TrialCirculation2;134(5):378
  13. Jiajie Liu and David W. L. Ma (2014).’‘The Role of n-3 Polyunsaturated Fatty Acids in the Prevention and Treatment of Breast Cancer” Nutrients. 6(11): 5184–5223.
  14. Heinze, VM; Actis, AB (February 2012). “Dietary conjugated linoleic acid and long-chain n-3 fatty acids in mammary and prostate cancer protection: a review”. International journal of food sciences and nutrition. 63 (1): 66–78.
  15. Chua ME, Sio MC, Sorongon MC, Morales ML (May–June 2013). “The relevance of serum levels of long chain omega-3 polyunsaturated fatty acids and prostate cancer risk: a meta-analysis”. Canadian Urological Association Journal. 7 (5–6): E333–43.
  16. Brasky TM, Darke AK, Song X, et al. (August 2013). “Plasma phospholipid fatty acids and prostate cancer risk in the SELECT trial”. J. Natl. Cancer Inst. 105 (15): 1132–41.
  17. Sydenham E, Dangour A, Lim W (2012) ”Omega 3 fatty acid for the prevention of cognitive decline and dementia” Cochrane Database of Systematic Reviews
  18. Grosso, G.; Pajak, A.; Marventano, S.; Castellano, S.; Galvano, F.; Bucolo, C.; Caraci, F. (2014). “Role of Omega-3 Fatty Acids in the Treatment of Depressive Disorders: A Comprehensive Meta-Analysis of Randomized Clinical Trials”. PLoS ONE. 9 (5)
  19. Miller PE, Van Elswyk M, Alexander DD (July 2014). “Long-chain omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid and blood pressure: a meta-analysis of randomized controlled trials”. American Journal of Hypertension. 27 (7): 885–96
  20. Mercury Levels in Commercial Fish and Shellfish (1990–2010) U.S. Food and Drug Administration. Accessed 14 January 2017
  21. Top 10 Fish Oil Supplements – LabDoor”. LabDoor. Accessed  14 January 2017
  22. Steenland K, Bertazzi P. (2004) ‘‘Dioxin Revisited: Developments Since the 1997 IARC Classification of Dioxin as a Human Carcinogen”. Environmental Health Perspectives. 112 (13) 1265-1268


13 thoughts on “The truth about Fish Oil

  1. Wow, this is a great in-depth review of a type of pill I have heard so much about but never really understood. You say that much of the health benefits of fish oil pills are not necessarly proven. I assume that these “benefits” are mostly pushed by fish oil companies. In any case, I don’t think they can hurt, like you say. I like sticking to natural fish, though.

    1. Hi Ben,

      Thanks for stopping by. You couldn’t be more correct – ,manufacturers are of course keen to sell their product. They will often take very weak evidence and exagerate the effects to impress you as a customer. That benefits them but ultimately leaves you out of pocket. This sort of marketing really winds me up and due to my background in biological sciences I thought I would try and make clear the actual benefits (or lack thereof) of major health and sport supplements.


  2. This was an interesting and educational read.

    I really appreciate your honesty. Many times, when I walk into a health store, I always get told that Omega 3, is extremely important and it can prevent heart attacks.

    As you article pointed out, it can help to improve general heart function in folks that have experienced a heart attack but no evidence to suggests that it ‘prevents’ it from happening.

    This is an article that I want to share with everyone that I know to show them that at times, we can be lead ‘astray’ in terms of what definitely helps and what does not.

    Thanks so much for this, looking forward to your future articles.


    1. Howdy Roopesh,

      The health and sport supplement industry as a whole is largely based on misleading people. That’s pretty much a fact. I’ve written extensively about multivitamin supplements and green tea extract (etc etc) in the past and the story is largely the same each time. For a healthy person, there is no strong evidence that taking vitamins or drinking green tea has much of a posititve physioloigcal impact. This is especially true of multivitamins.

      Fish oils lie somehwere in the middle. The benefits are no where near as numerous as some people claim but decent evidence suggest it may be useful in the treatment of some mental disorders (alongside established treatments) and also for people with a history of heart problems.

      Manufacturers see the words ‘heart, health, fish oil’ and jump to conclusions about what fish oil can actually do for the average person.

      The point of this website is to go through common supplements and the scientific literature behind them so you don’t spend loads of money on things that simply won’t help you.

      Glad you liked what you read. Don’t forget to pop back for more – I update frequently.


  3. I used to consume fish oil tablets when I was trying to lose weight. I only took natural supplements; fish oil and green tea.

    My tip for buying fish oil – try to search for tablets with some orange or lemon scene to it. It will help a lot especially for the first timer.

    I usually eat them three times before meals, but of course it depends on the size of the pills.


    1. Hi A Habil

      I’m not sure how well you took in the article but my main point was actually how fish oil supplements only seem to be beneficial in a few limited situations or if you don’t eat enough fish and nuts in general. They certainly have no conclusive role or benefit in weight loss.

      You also talk about green tea – I have written an extensive article thoroughly debunking the myth that green tea helps with weight loss. There is no solid science that supports this.

      I’d recommend sticking to a balanced diet and exercise for weight loss. Supplements won’t do the job for you, green tea and fish oils included.


  4. It’s so true that many claim that their pill will improve your heath dramatically. I have been taking vitamins for over 30 years and i do still believe there are many health benefits. But don’t expect you heath and body to just change over night fro taking a supplement like fish out. It takes proper eating and excersise to improve you overall heath.

  5. Really informative read, thank you.

    I always struggle with which supplwmwnts I should be taking, to your point,every manufacture almost makes you feel like you can’t survive without thier product, Omega-3 being a perfect example. I love fish anyway, so I’m guessing if i eat white fish at least once a week I would be getting a decent intake of Omega 3? For me it’s hard to work out what I should be taking on top of my diet, and what I will already be getting enough of from simply eating well. any tips gratefully recieved.

    1. Hi Mike,

      Thanks for the input. You are completely right in thinking that supplement companies will try to have you believe that you aren’t ‘your best self’ without their product. The truth is usually far from that. Supplements like whey protein are great if you don’t eat a lot of protein in general. Fish oil tablets are a good idea if you don’t eat a lot of fish or certain nuts like walnuts.

      Eating fish once a week is likely more than adequate. You could always supplement with fish oil capsules and see if you notice any performance differences but it is highly unlikely.

      My best advice is simply to maintain a balanced diet. For most people, eating a good amount of fruit and veg alongside varied meats, nuts and grains and things like rice and pasta will avoid any nutrient deficiencies.

      If you are trying to get bigger and stronger, increase your calories across the board in all food groups. However eating truck loads of protein won’t necessarily help you get stronger faster. Carbs and healthy fats are 100% needed as well if you want to be at your peak.

      Thanks for stopping by

  6. First off I just want to thank you for going so indept with your description on fish oils. really helpful.

    I was always under the impression fish oils were good for joint health also. do you know whether this is true? I have bad elbows and knees from years of sports and consume fish oils daily pretty much for this reason. If they are not then I would stop

    1. Hi Kurtis,

      Cheers, glad you liked the article. I haven’t looked too much into Omega-3 and joint health studies. All I can say on this topic without researching further is that they may potentially be beneficial due to their anti-inflammatory properties. However, pharmaceutical drugs which target inflammation will have a much greater impact. I woudn’t take fish oil supplements just for the anti-inflammation effects.

      I wouldn’t necessarily stop taking them all together either. From what I’ve found, fish oils, specifically omega 3s are important in normal health as we can’t synthesis them ourselves.

      However, the benefits of supplementing are much harder to determine. If you already consume good food sources of omega 3s (detailed in the article) then supplementing probably isn’t neccessary. If you don’t like oily fish or nuts like walnuts then supplementing might be a good idea.

  7. This is an amazing break down of the popular fish oil that everyone seems to be taking these days. You outdid yourself, this one is super informative.

    So it’s safe to conclude that the pros outweight the cons when it comes to supplementing with fish oil. Still, I’ve personally never thought that the toxins that exist in the seas and oceans affect the fish that we consume. I guess this is what happens when you only consume them in their readily available form.

    Any Fish Oil brands to recommend by the way?

    1. Hi Simon.

      Thanks, what a glowing review – glad you liked the article ! This article required in-depth investigation of the literature. Unlike some things like green tea extract which I’ve written about before and where the claimed benefits are essentially non-existent, Omega-3s are much harder to dissect and probably do have beneficial and therapeutic effects in a number of situations. So much so that it could be worth while supplementing if you don’t already eat foods that contain them such as walnuts and oily fish.

      I’ve linked a couple of products right at the bottom of the article. The two standard ones I’ve used before -essentially the same product but from two good, reputable sellers. The third option is actually an extract from algae and because of this is suitable for vegetarians 🙂


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