Nutritional Medicine Updates

Do You Eat Two Portions Of Fish Per Week?

omega 3 fish oil benefits

If you eat the recommended two portions of fish per week, one of which is oily, then you are likely to live longer as a result. A huge diet and health study from the US, involving 421,309 men and women who were followed-up for 16 years, looked for links between fish consumption and risk of death from any medical cause.

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Men and fish intake

For men, those with the highest fish intake were 9% less likely to die during the study period than those with the lowest fish intake. When causes of death were looked at, high intakes of fish lowered the risk of fatal cardiovascular disease (heart attack or stroke) by 10%, cancer death by 6%, and respiratory disease death by 20% and death from chronic liver disease by 37%.

Women and fish intake

Among women, those with the highest fish intake were 8% less likely to die during the study follow-up than those with the lowest intakes, and those who ate the most fish were 10% less likely to die from cardiovascular disease and were an astonishing 38% less likely to die from Alzheimer’s disease.

Why is fish so good to eat?

Fish provides numerous nutritional benefits, including protein, long-chain omega-3 fatty acids (EPA and DHA), vitamin D3, and minerals such as iodine and

The most protective factor in fish appears to be the omega-3s. When researchers calculated dietary intakes of long-chain omega-3 fatty acids of those taking part in the study, those with the highest intakes of EPA and DHA were 15% less likely to die from cardiovascular disease for men, and 18% for women.

It seems best to avoid fried fish, as fried fish did not have any protective effects against male mortality and actually increased the female risk of dying from any cause, but especially from cardiovascular and respiratory diseases.

This study supports current recommendations for eating fish, but also found that it’s best to use non-frying methods of cooking fish such as baking, grilling or baking.

What about the negative headlines?

The above massive study, which showed ‘robust’ evidence of benefit from obtaining long-chain omega-3s from fish was, unfortunately, published at the same time as another, lesser study which stole all the headlines. This second study analysed the results from 79 clinical trials, involving 112,059 people (almost a third of a million fewer than in the far larger positive study above), to assess the effects of omega-3 fatty acids against all causes of death, including heart attack and stroke.

Unlike the previous analysis, in which fish intakes in the general population were assessed over 16 years, most studies in this analysis looked at the effects of taking omega-3 fish oil supplements, or plant-based short-chain omega-3s (mostly alpha-linolenic acid from omega-3 enriched foods) for relatively short periods of time from 12 months to 72 months. And, rather than involving a selection of people from the general population, it involved people at high risk of heart disease who were taking supplements in the hope of preventing either a first heart attack or stroke (primary prevention), or a recurrent episode (secondary prevention).

This analysis found little or no effect of increasing intakes of long-chain omega-3s with a non-significant 2% reduction in death from any cause, and a 5% reduction in risk of a cardiovascular death.

Although the results were painted as negative, there was a suggestion that omega-3 fish oil reduced coronary heart disease events by 7% but after a sensitivity analysis of the mathematical model used, the overall conclusion was that supplements probably made little or no difference to coronary heart disease event risk.

Why I still recommend fish oil supplements

Fish oil supplements are not a magic cure. They are intended to supplement the diet for those who prefer not to eat fish, for whatever reason. To expect them to significantly reduce the risk of death after taking them for just a few months – especially in people at high risk of a heart attack or stroke, or who have already experienced one – seems rather optimistic.

Diet should always come first, but if you don’t eat the recommended intake of two portions (150g each) of fish per week, once of which should be oily (eg salmon, mackerel, herring, sardines, pilchards, fresh but not tinned tuna) then fish oil supplements can help to ensure you obtain sufficient essential fatty acids in your diet.

Omega-3s are essential for health and must come from the diet; we cannot make them ourselves and only convert a few of the short-chain omega-3s (less than 5%) on to the most important long-chain omega-3s.

The long chain omega-3s, DHA and EPA, are incorporated into cell membranes to maintain their flexibility, and act as building blocks to make hormone-like substances that damp down inflammation.

Within the EU, fish oil supplements have a number of authorised health claims as follows:

  • DHA and EPA contribute to the maintenance of normal blood pressure
  • DHA and EPA contribute to the maintenance of normal blood triglyceride levels
  • EPA and DHA contribute to the normal function of the heart
  • DHA contributes to maintenance of normal brain function
  • DHA contributes to the maintenance of normal vision
  • DHA contributes to the normal brain development of the foetus and breastfed infants.
  • DHA contributes to the normal visual development of infants up to 12 months of age.
  • DHA contributes to the normal development of the eye of the foetus and breastfed

Fish oil reduces inflammation

The long-chain omega-3s in fish oil are converted into substances (series 3 prostaglandins and series 5 leukotrienes) that reduce inflammation. As a result, omega-3 fish oil has a pain-killing effect similar to that of non-steroidal anti-inflammatory drugs NSAIDs).

Many common diseases are associated with inflammation, even health problems that don’t have obvious inflammatory symptoms (redness, heat, swelling and pain) but which are associated with an accumulation of inflammatory cells when examined under the microscope. These inflammatory diseases include all forms of arthritis, eczema, psoriasis, asthma and acne. Even high blood pressure, coronary heart disease, depression and dementias are associated with low-grade inflammation of artery walls or nerve sheaths, for example. Poor intakes of omega-3s may promote these inflammatory conditions.

Omega 3 and depression

The long-chain omega-3s found in fish oil have important actions in the brain. As well as damping down inflammation, EPA is involved in cell signalling and helping brain cells respond to stimuli, while DHA is incorporated into brain cell membranes to speed the transmission of electrical and chemical messages.

Good intakes of oily fish are associated with lower rates of unhappiness and depression with studies involving over 255,000 people showing that people who eat the most fish and have the highest DHA and EPA intakes are 22% less likely to experience depression than those who eat little or no fish. The optimum intake for brain health and mood was assessed as 1.8g omega-3 per day.

The beneficial effects of omega-3 on mood are seen quite quickly. In one study involving young adults with depression, a significant uplift in mood was seen after taking omega 3 supplement for 21 days, by which time two-thirds (67%) of those taking omega-3 fish oil no longer had significant depression symptoms compared with only 20% of those taking placebo.

Omega 3 for anxiety

Anxiety and depression often go hand in hand and, just as fish oil protects against depression, it also reduces anxiety symptoms. So much so that, in people with major depressive disorder, researchers can distinguish those who also experienced anxiety from those who were not anxious by checking their blood levels of EPA and DHA, which were especially low in those who also experienced anxiety. What’s more, those with the lowest omega 3 levels had the most severe anxiety.

The anxiety lowering effects of omega-3 can also help to reduce exam stress. A group of healthy medical students undergoing exams were asked to take either an omega-3 fish oil supplement (2.5 g per day) or a placebo. Those students who took omega-3 supplements had a 20% reduction in anxiety symptoms compared with placebo.

Omega-3 for dementia

Oxford scientists have found that taking omega-3 fish oil plus high dose B vitamins can slow the progression of brain shrinkage in people with a form of cognitive impairment that can progress to Alzheimer’s disease. A group of 168 people with mild cognitive impairment took high-dose B vitamins (folic acid 0.8 mg, vitamin B6 20 mg, vitamin B12, 0.5 mg) or placebo for two years.

Brain scans showed that taking B vitamins slowed the rate of brain atrophy by 40% compared with placebo – but only if high blood levels of omega-3 fatty acids were also present. In those who had a raised level of the harmful amino acid, homocysteine, the rate of brain shrinkage reduced by 70% as B vitamins help to convert homocysteine into other harmless substances. Again, no significant effect on the rate of atrophy was seen in those with low omega-3 levels.

So, if you are taking a B vitamin complex for brain health, eat more fish (or take a fish oil supplement) too. This suggest that Alzheimer’s-related brain atrophy, or shrinkage, might be slowed through dietary interventions with omega-3 and B vitamins and has been hailed as a major breakthrough in dementia prevention.

How much omega-3 do you need?

There is no international consensus on the exact omega-3 intake needed for optimum health. The International Society for the Study of Fatty Acids and Lipids recommend an intake of at least 500mg EPA and DHA per day.

UK: For general health, the UK government recommend a minimum intake of 450mg long-chain omega 3 fish oils (DHA and EPA) per day.

EFSA: The European Food Safety Authority recommend 250mg EPA + DHA per day for the general adult population.

US: Intakes of at least 250mg long-chain omega-3s are recommended (or 1.6g total omega-3 per day for men, and 1.1g per day for women).The AMerican Heart Association recommend intakes of 500mg or more EPA and DHA for the general adult population, and 1g per day from oily fish for patients with coronary heart disease.

NATO recommend an intake of 300mg to 400mg per day of EPA and DHA for the general adult population

Australia: the National Heart Foundation of Australia recommend 500 mg EPA and DHA per day, obtained through fish, fish oil capsules or enriched foods and drinks.

Oily fish is the best dietary source of long-chain omega-3s, with white fish supplying small amounts, as follows:


Portion size (grams)

Total long-chain omega-3s (DHA/EPA) per portion (grams)

Pilchards (in tomato sauce)110g2.86g
Tuna (fresh)150g1.95g
Sardines in tomato sauce100g1.67g
Tinned Salmon (in brine, drained)100g1.55g
Tinned Tuna (in oil, drained)45g0.17g
Tinned Tuna (in brine, drained)45g0.08g

Omega 3 Supplements

If you eat no fish, your supplement needs to provide at least 450mg to 1gram EPA/DHA per day for general health. Typically, a 1g capsule of high-strength fish oil contains around 500mg of the important long-chain EPA and DHA (check label claims).

If you prefer a vegetarian source, or are allergic to fish, then flaxseed oil is an excellent source of the short chain omega-3, alpha-linolenic acid, an omega-3 of which small amounts (5% or less) are converted on to EPA and DHA in the body. The most effective vegetarian sources are therefore marine algae extracts – which is exactly where oily fish get their own DHA and EPA.

Select a pharmaceutical-grade omega-3 fish oil supplement made to GMP standards to ensure they are virtually free from marine pollutants.

Click here to see my recommended omega 3 supplements on Amazon.

Omega-3 safety

The European Food Safety Authority have concluded that fish oil supplements providing up to 5g long-chain omega 3 per day raise no safety concerns for adults.

As fish oil has a blood thinning effect, check with your doctor before taking if you are on blood thinning or antiplatelet medication. However, no significant increase in blood clotting time is expected at total daily fish oil supplements supplying EPA and DHA at doses of 3g per day, or less.

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Dr Sarah Brewer
QUORA EXPERT - TOP WRITER 2018 Dr Sarah Brewer MSc (Nutr Med), MA (Cantab), MB, BChir, RNutr, MBANT, CNHC Cert IoD qualified from Cambridge University with degrees in Natural Sciences, Medicine and Surgery. After working in general practice, she gained a master's degree in nutritional medicine from the University of Surrey. Sarah is a registered Medical Doctor, a registered Nutritionist and a registered Nutritional Therapist. She is an award winning author of over 70 popular self-help books and a columnist for Prima magazine.

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