Are fish oil capsules beneficial?

Question

Page 28 of the February 2018 edition of Which? magazine says,

(You don't need...)
Fish oils such as Omega 3 capsules
Unless you are advised to take these, you don't need to. Studies show that fish oil's positive benefits are gained though eating oily fish, not supplements.

Is this true? What are these studies? Assuming eating oily fish has positive benefits, to what extent is it true that benefits are not gained through supplements (fish oil capsules)?

Is this lack of benefit equally true for diets which are already e.g. mostly-vegan, which don't need to eat fish in order to "eat less red meat etc." (or whatever other beneficial side-effects of eating fish might be)?

In case it matters I'm especially interested in "fish oils" as a source of DHA, more than omega-3.

Answer 1

There is insufficient evidence to say that intake of fish oil supplements (high in omega-3 fatty acids DHA and EPA) reduce the risk of heart or other disease.

1) Omega-3 intake for cardiovascular disease (Cochrane, 2018):

Moderate- and high-quality evidence suggests that increasing EPA and DHA has little or no effect on mortality or cardiovascular health (evidence mainly from supplement trials). Previous suggestions of benefits from EPA and DHA supplements appear to spring from trials with higher risk of bias.

2) Fish oil supplementation and insulin sensitivity: a systematic review and meta-analysis (Lipids in Health and Disease, 2017):

This systematic review and meta-analysis showed that fish oil supplementation did not affect estimates of insulin sensitivity overall. However, short-term fish oil supplementation could improve insulin sensitivity among patients with metabolic disorders, which could be a significant intervention as secondary prevention for the T2DM and metabolic syndrome.

3) How does high DHA fish oil affect health? A systematic review of evidence (Tandofline, 2018):

Although there is sufficient evidence to strongly suggest that DHA plays a series of important and fundamentally beneficial and health promoting roles, the currently available scientific literature describing the roles and potential metabolic effects of DHA, as an individual nutrient and/or in comparison to EPA, is far from conclusive. The exact mechanisms and the extent of these actions are not yet fully elucidated. DHA appears to play important roles, different to those of EPA, in heart, cardiovascular, brain and visual functions.

4) Omega-3 Supplements: In Depth (National Center for Complementary and Integrative Health, 2018):

• Research indicates that omega-3 supplements don’t reduce the risk of heart disease. However, people who eat seafood one to four times a week are less likely to die of heart disease.
• High doses of omega-3s can reduce levels of triglycerides.
• Omega-3 supplements may help relieve symptoms of rheumatoid arthritis.
• For most other conditions for which omega-3 supplements have been studied, the evidence is inconclusive.

5) FDA Announces New Qualified Health Claims for EPA and DHA Omega-3 Consumption and the Risk of Hypertension and Coronary Heart Disease (The US Food and Drug Administration, 2019):

The agency found that while there is some credible evidence suggesting that combined intake of EPA and DHA from conventional foods and dietary supplements may reduce the risk of hypertension by lowering blood pressure, this evidence is inconclusive and highly inconsistent.

Omega-3 supplements and vegetarians/vegans

Most vegans refuse to take fish oil supplements (here: table 5), so this is why there are no related studies. In one small 1996 study, the intake of DHA from algae for 6 weeks increased DHA and EPA levels and slightly decreased LDL/HDL ratio in vegetarians.

Vegetarians and vegans, in general, consume much less saturated fats than omnivores (Nutrients, 2014).

According to one 2017 systematic review, vegan diets are associated with a decreased risk of ischemic heart disease and cancer, which triggers the question if fish and fish oil supplements are that beneficial at all.

In one 2016 review, they have found an association between vegetarian diets and lower risk of ischemic heart disease and diabetes.

Here are also two small studies: in one, vegan and vegetarian diets were associated with significantly lower levels of triglycerides and LDL cholesterol and in another one, vegan, but not vegetarian diets, were associated with lower LDL levels compared to omnivores.

This very limited, but quite conclusive, evidence suggests that vegans and vegetarians who tend to consume less saturated fat and have lower cholesterol and triglyceride levels than omnivores may not benefit significantly from omega-3 supplements.

It is also good to know that fish oil can reduce triglyceride, but not LDL cholesterol levels (Pharmacy and Therapeutics).

Answer 2

Are fish oil capsules beneficial?

Yes, UNLESS you eat fish (duh!)

Howard LeWine, M.D., Chief Medical Editor, Harvard Health Publishing writes:

But the evidence for improving heart health is mixed. ... However, when researchers looked at subgroups of people who don’t eat any fish, the results suggested they may reduce their cardiovascular risk by taking a fish oil supplement.

As always, when you choose your advisor, you choose your advice.