What does omega-3 do to your body?

What does omega-3 do to your body? Two things above all. It helps build your cell membranes, with a strong concentration in your brain and retina, and it supplies the building blocks for compounds that dampen inflammation. What omega-3 does beyond that depends on form and dose, and that is where it gets interesting.

The three largest trials on omega-3 contradict each other. That sounds unhelpful, but their differences explain exactly how it works.

What does omega-3 do to your body at cell level?

Omega-3 fatty acids are built into the wall of your cells. That wall is made of fats, and the type of fat determines how flexible and permeable the membrane is. More omega-3 means a more flexible cell wall, which matters most in tissue that has to pass signals quickly.

There are three forms worth knowing. ALA comes from plant sources such as flaxseed and walnut. EPA and DHA come from oily fish and algae. Your body can convert ALA into EPA and DHA, but does so inefficiently: conversion to DHA stays below five percent in most people.

DHA is mainly structural. It makes up roughly 40 percent of the polyunsaturated fatty acids in your brain and around 60 percent in your retina. EPA is more functional and provides the basis for anti-inflammatory signalling compounds.

What do the large trials say?

This is where most articles go wrong, by citing one positive trial and leaving out the rest. The three large studies together give a sharper picture, precisely because they reach different answers.

In REDUCE-IT the treated group had 17.2 percent cardiovascular events against 22.0 percent on placebo (Bhatt et al., 2019. PMID 30415628). In STRENGTH, with a comparable risk population but EPA and DHA together, the result was 12.0 against 12.2 percent: no difference (Nicholls et al., 2020. PMID 33190147).

VITAL tested the question most people are actually asking, namely whether an ordinary fish oil supplement protects a healthy population. Among 25,871 participants, 840 mg a day did not lower the number of cardiac events or cancer cases (Manson et al., 2019. PMID 30415637).

My reading of this: omega-3 in supplement form is not general protection for someone already eating well. In a specific group, with high triglycerides and a high dose of pure EPA, the picture differs. That has become a medicine, not dietary advice.

How much omega-3 do you need?

For the ordinary situation the European food authority EFSA is clear. An intake of 250 mg of EPA and DHA per day contributes to normal heart function. That is the only claim in this area approved in Europe.

You reach that 250 mg with roughly one portion of oily fish a week. Herring, mackerel, salmon and sardines are the familiar sources. The Dutch nutrition centre Voedingscentrum therefore advises fish weekly, preferably an oily variety.

The doses used in REDUCE-IT sit sixteen times above that, and are reserved for people under treatment. A random capsule from the supermarket is nowhere near it.

What can you measure?

This is the appealing part of omega-3 compared with most nutrients: your status is genuinely measurable. The omega-3 index expresses the percentage of EPA and DHA in the membrane of your red blood cells, reflecting your intake over recent months.

Take two people who both say they eat enough fish, one having herring weekly and the other cod monthly: that is roughly a factor 4 difference in EPA and DHA intake. Their perception is identical. Their index is not, and only with that result does the difference become discussable.

That makes omega-3 one of the few nutrition topics where you can genuinely check a change. The background sits on the marker page for the omega-3 index.

What does omega-3 do to inflammation?

EPA supplies the raw material for signalling compounds that help bring inflammatory responses to a close. That is a more nuanced story than suppressing inflammation: the body uses them to end a reaction cleanly rather than letting it simmer on.

In practice you see that as a modest effect on inflammatory values such as hs-CRP, and in its use for rheumatic joint complaints. Do not expect a dramatic shift in your blood values from a supplement alone.

How food and inflammatory values relate is worked out in lowering inflammation values with food. The broader picture of eating and blood values is in nutrition and your blood values.

Frequently asked questions

What is the difference between EPA and DHA?

DHA is mainly a building block and sits concentrated in the brain and retina. EPA provides the basis for anti-inflammatory signalling compounds and has more influence on blood clotting and triglycerides. Most supplements contain both, in varying ratios.

Does algae oil work as well as fish oil?

For DHA it does, since algae are the original source fish get their DHA from. The EPA content is lower in many algae products, so I would check the label if you are specifically after EPA.

When is the best time to take omega-3?

With a meal containing fat, because absorption is better then. The time of day matters little. For people troubled by fishy burps, taking it with the evening meal often helps.

Can you get too much omega-3?

At high doses the risk of bleeding rises, which matters most with blood thinners or around surgery. In STRENGTH, gastrointestinal complaints were also clearly more common in the omega-3 group. Talk to your doctor before using high doses. A similar dose story applies to spices, see what does clove do to your body.

References

• Bhatt DL, et al. Cardiovascular Risk Reduction with Icosapent Ethyl for Hypertriglyceridemia (REDUCE-IT). New England Journal of Medicine. 2019. PMID 30415628. PubMed
• Nicholls SJ, et al. Effect of High-Dose Omega-3 Fatty Acids vs Corn Oil on Major Adverse Cardiovascular Events (STRENGTH). JAMA. 2020. PMID 33190147. PubMed
• Manson JE, et al. Marine n-3 Fatty Acids and Prevention of Cardiovascular Disease and Cancer (VITAL). New England Journal of Medicine. 2019. PMID 30415637. PubMed