Where do omega-3s go in the body?
Omega-3s pass from the intestine to the lymph and then to the blood, which places them in cell walls, especially in the brain and retina. The liver turns very little plant ALA into DHA: 0 to 9%. An adult brain holds about 5 g.
Where do omega-3s go, from the plate to the membranes?
ALAPlant omega-3s
EPADHAFish omega-3s, or made by the liver
CO₂Carbon dioxide
Simplified organs and routes; the small dots show the direction of travel, not the amounts. The passage through the intestine is detailed in Where do the fats we eat go? Tap an organ to go to its step.
The path in text, the foods, and where these numbers come from
| Step | Number | What happens |
|---|---|---|
| 1. Omega-3s arrive on the plate | 1.1 to 1.6 g of ALA per day recommended for adults | ALA comes from flaxseeds, chia seeds, walnuts, and canola and soybean oils. EPA and DHA come mostly from oily fish: microalgae make them, and fish build them up by eating these algae. |
| 2. The intestine absorbs them like other fats | ≈ 95% of the fats eaten are absorbed | In the small intestine, bile and enzymes cut up the fats. The intestinal cells then pack the omega-3s into large droplets, chylomicrons, which pass through the lymph before reaching the blood. |
| 3. The liver lengthens a little ALA | 0 to 9% of ALA becomes DHA | The liver can lengthen ALA (18 carbons) into EPA (20 carbons), then into DHA (22 carbons), but very little: generally less than 15% (NIH). Into DHA: 0 to 3.8% in young men, 9% in young women. |
| 4. A large share is used as fuel | 22 to 33% of ALA burned in 24 hours | Part of the ALA is never lengthened: cells burn it to make energy, and it leaves in the breath as carbon dioxide. The rest goes into membranes or into stored fat. |
| 5. The blood distributes them | 120 days of memory in red blood cells | In the blood, omega-3s travel in lipoproteins and enter the membrane of red blood cells. Their level in plasma changes with the last meal; the level in red blood cells reflects roughly the last 120 days. |
| 6. They settle in membranes | ≈ 5 g of DHA in an adult brain | EPA and DHA enter cell walls, especially in the brain, the retina and sperm. They are also used to make messengers, generally less inflammatory than those from omega-6s. Overall: the liver makes too little DHA to cover needs, so DHA comes mostly from the plate. |
| Food (NIH) | Serving | ALA | EPA | DHA |
|---|---|---|---|---|
| Flaxseed oil | 1 tablespoon | 7,26 g | ||
| Chia seeds | 28 g | 5,06 g | ||
| Walnuts | 28 g | 2,57 g | ||
| Whole flaxseeds | 1 tablespoon | 2,35 g | ||
| Canola oil | 1 tablespoon | 1,28 g | ||
| Soybean oil | 1 tablespoon | 0,92 g | ||
| Farmed Atlantic salmon, cooked | 85 g | 0,59 g | 1,24 g | |
| Wild Atlantic salmon, cooked | 85 g | 0,35 g | 1,22 g | |
| Herring, cooked | 85 g | 0,77 g | 0,94 g | |
| Sardines in tomato sauce, canned | 85 g | 0,45 g | 0,74 g | |
| Mackerel, cooked | 85 g | 0,43 g | 0,59 g | |
| Wild rainbow trout, cooked | 85 g | 0,40 g | 0,44 g | |
| Light tuna in water, canned | 85 g | 0,02 g | 0,17 g | |
| Shrimp, cooked | 85 g | 0,12 g | 0,12 g | |
| Pacific cod, cooked | 85 g | 0,04 g | 0,10 g | |
| Egg, cooked | 1 egg | 0,03 g | ||
| Chicken breast, roasted | 85 g | 0,01 g | 0,02 g |
- humanIntake. ALA: 1.1 g per day for a woman, 1.6 g for a man (NIH). In France: ALA 1% of energy, 250 mg of EPA and 250 mg of DHA per day for adults (ANSES).
- humanAbsorption. About 95% of the fats eaten are absorbed, omega-3s included; they go into chylomicrons and then the lymph (NIH).
- humanConversion. Generally less than 15% according to the NIH, for EPA and DHA together. Young women: 21% of ALA becomes EPA, 9% DHA (Burdge and Wootton, 2002). Young men: 6% into EPA and 3.8% into DHA (Emken et al., 1994); no labeled DHA in 21 days in another study (Burdge et al., 2002). Small studies with labeled ALA.
- humanALA burned. 22% of labeled ALA leaves as carbon dioxide within 24 hours in young women, 33% in young men (Burdge et al., 2002).
- humanBrain. About 5 g of DHA in the brain, a figure the authors consider preliminary (Umhau et al., 2009).
- hypothesisDrawing. The dots show the direction of travel. The flame sums up the energy drawn from ALA in all cells.
Where do EPA and DHA settle?
EPADHAOmega-3s carried by the blood
Red blood cell
Simplified drawing; the heart beats here at 60 beats per minute, as an example. The gauge zones come from observational studies. Tap an organ to go to its step.
The steps in text, and where these numbers come from
| Step | Number | What happens |
|---|---|---|
| 1. The brain keeps a large store of DHA | ≈ 5 g of DHA in an adult brain | DHA is one of the most abundant fats in brain membranes, especially in gray matter. The brain cannot make it: it receives it from the blood. |
| 2. A gate lets it into the brain | 3.8 mg of DHA enter the brain per day | DHA crosses the wall of the brain's small vessels through a gate, Mfsd2a, which takes it attached to a small molecule, LPC. Mice lacking this gate have much less DHA in the brain. The store renews slowly: half in about 2.5 years. |
| 3. The retina lines its light sensors with it | 3rd trimester of pregnancy: DHA builds up there | At the back of the eye, DHA is a major structural fat of the membranes of the light sensors, in their outer segment. It builds up there mainly during the 3rd trimester of pregnancy. |
| 4. Red blood cells serve as a marker | 3 to 5% usual Omega-3 Index in the West | The Omega-3 Index is the share of EPA and DHA among the fats in the red blood cell membrane. It reflects roughly the last 120 days and gives an idea of what other tissues contain. |
| 5. The heart and the Omega-3 Index | 8% or more: the fewest heart deaths observed | In observational studies, an index of at least 8% went with the fewest deaths from heart causes, an index of 4% or less with the most. This is a statistical link: it does not prove that omega-3s are the cause. The big trials are in tab 4. |
- humanBrain. About 5 g of DHA (preliminary figure); 3.8 mg per day enter the brain, measured by PET imaging in 14 adults; half-life of about 2.5 years; DHA is taken up more strongly by gray matter (Umhau et al., 2009). DHA is mostly concentrated in gray matter (Calder, 2016).
- animalThe Mfsd2a gate. The brain does not make DHA; the Mfsd2a gate, found only in the walls of brain vessels, lets it in as LPC-DHA. Mice without this gate: much less DHA in the brain (Nguyen et al., 2014).
- humanRetina and pregnancy. DHA is a major structural fat of the outer segments of the light sensors (SanGiovanni and Chew, 2005). It builds up mainly in the 3rd trimester; the retina is finished at birth, the brain continues for the first 2 years (NIH).
- humanOmega-3 Index. EPA and DHA as a % of red blood cell fatty acids; 3 to 5% in the West with little fish, about double in Japan, 9.6% in 262 Japanese men (Schuchardt et al., 2022); reflects about 120 days (NIH). Index of 8% or more: lowest observed risk of heart death; 4% or less: the highest (Harris and von Schacky, 2004). Japan gauge drawn from 6 to 10%, around this value.
- hypothesisDrawing. The heart beats at 60 beats per minute as an example; the purple dots on the red blood cell illustrate the DHA in its membrane.
Why do omega-6s hold back omega-3s?
ALAEPADHAOmega-3s
LALinoleic acid (omega-6)
AAArachidonic acid (omega-6)
Messengers made from EPA, then from arachidonic acid
Schematic diagram: numbers of molecules and speeds are illustrative. The size of the red messengers only says that they are generally more potent.
The steps in text, and where these numbers come from
| Step | Number | What happens |
|---|---|---|
| 1. Two families, the same enzymes | 2 families share the same enzymes | The body can make neither ALA (omega-3) nor linoleic acid (omega-6): both come from the plate. To lengthen them, it uses the same enzymes, the desaturases. When one family occupies the enzymes, the other is lengthened less. |
| 2. More omega-6s, less ALA lengthened | 40 to 54% less ALA conversion | In 7 young men, doubling the linoleic acid in meals, from 15 to 30 g per day, reduced the share of ALA lengthened into EPA and DHA by 40 to 54%. |
| 3. Two rival messengers | 20 carbons for EPA and arachidonic acid | EPA (omega-3) and arachidonic acid (omega-6) are used to make messengers, the eicosanoids. Those from omega-6s are generally more potent for inflammation, narrowing of vessels and clumping of platelets. The more EPA and DHA there is relative to arachidonic acid, the more the balance tips toward less inflammation. |
| 4. What about the omega-6 to omega-3 ratio? | 4 to 1 linoleic acid and ALA in the ANSES benchmarks | People often talk about a good ratio between omega-6s and omega-3s. No ideal ratio has been defined (NIH), and ANSES considers it of little use, except when ALA is lacking or linoleic acid is in excess. For most researchers, the level of EPA and DHA in the blood matters much more. |
- humanSame enzymes. Omega-3s and omega-6s compete for the same desaturation enzymes: ALA slows the lengthening of linoleic acid, and vice versa (NIH).
- humanExperiment. 7 young men, fatty acids labeled with deuterium: going from 15 to 30 g of linoleic acid per day reduces ALA conversion by 40 to 54% (Emken et al., 1994).
- humanMessengers. Eicosanoids made from omega-6s are generally more potent for inflammation, constriction of vessels and clumping of platelets, with exceptions (NIH).
- humanRatio. No ideal ratio defined; most researchers consider that the level of EPA and DHA in the blood matters more than lowering linoleic acid (NIH). The ratio is of little interest except with a lack of ALA or an excess of linoleic acid (ANSES). ANSES benchmarks for an adult: linoleic acid 4% of energy, ALA 1%; “4 to 1” comes from these two benchmarks; ANSES advises staying under 5 to 1 (Afssa, 2010).
- hypothesisDrawing. The doubled line of omega-6s in step 2 and the fading line of omega-3s illustrate the direction of the effect, not its exact size.
Do omega-3 supplements protect the heart?
Each bar shows the risk with omega-3s compared with placebo, with its margin of uncertainty. Right of the line: fewer events than with placebo; left: more. A bar that touches the line shows no clear difference.
Fewer events than with placeboMore than with placeboNo clear difference
1 g per day of EPA and DHA, adults
Major cardiovascular eventsVITAL, Manson et al., 2019: 25,871 adults, 5.3 years
‹ more riskless risk ›placebo
8% fewer on average, but the margin runs from 20% fewer to 6% more: no clear difference.
Heart attackVITAL, Manson et al., 2019: secondary outcome
‹ more riskless risk ›placebo
28% fewer heart attacks (10 to 41%). Secondary outcome: a result still to be confirmed.
CancersVITAL, Manson et al., 2019
‹ more riskless risk ›placebo
No clear difference.
Serious vascular eventsASCEND, Bowman et al., 2018: 15,480 people with diabetes, 7.4 years
‹ more riskless risk ›placebo
8.9% versus 9.2% with placebo (olive oil): no clear difference.
4 g per day, people at high cardiovascular risk
Purified EPA (icosapent ethyl)REDUCE-IT, Bhatt et al., 2019: 8,179 people, 4.9 years
‹ more riskless risk ›placebo
17.2% versus 22.0%: 25% fewer events. The placebo was a mineral oil, perhaps not neutral (NIH).
EPA and DHASTRENGTH, Nicholls et al., 2020: 13,078 people
‹ more riskless risk ›placebo
12.0% versus 12.2% with placebo (corn oil): no difference; trial stopped early.
Side effect
Atrial fibrillationGencer et al., 2021: 7 trials, 81,210 people
‹ more riskless risk ›placebo
25% higher risk (7 to 46%), more above 1 g per day (49% higher).
Eyes
Age-related macular degenerationAREDS2, 2013: 4,203 people, 5 years
‹ more riskless risk ›placebo
31% of eyes progressed to an advanced form, versus 31% with placebo: no difference. 350 mg of DHA and 650 mg of EPA per day, added to the AREDS vitamin mix. Margin at 98.7%; the calculation counts eyes, not people.
The trials in text, and what these numbers are worth
| Measure | Study | Hazard ratio (margin) | What it means |
|---|---|---|---|
| Major cardiovascular events | VITAL, Manson et al., 2019: 25,871 adults, 5.3 years | 0,92 (0,80 à 1,06) | 8% fewer on average, but the margin runs from 20% fewer to 6% more: no clear difference. |
| Heart attack | VITAL, Manson et al., 2019: secondary outcome | 0,72 (0,59 à 0,90) | 28% fewer heart attacks (10 to 41%). Secondary outcome: a result still to be confirmed. |
| Cancers | VITAL, Manson et al., 2019 | 1,03 (0,93 à 1,13) | No clear difference. |
| Serious vascular events | ASCEND, Bowman et al., 2018: 15,480 people with diabetes, 7.4 years | 0,97 (0,87 à 1,08) | 8.9% versus 9.2% with placebo (olive oil): no clear difference. |
| Purified EPA (icosapent ethyl) | REDUCE-IT, Bhatt et al., 2019: 8,179 people, 4.9 years | 0,75 (0,68 à 0,83) | 17.2% versus 22.0%: 25% fewer events. The placebo was a mineral oil, perhaps not neutral (NIH). |
| EPA and DHA | STRENGTH, Nicholls et al., 2020: 13,078 people | 0,99 (0,90 à 1,09) | 12.0% versus 12.2% with placebo (corn oil): no difference; trial stopped early. |
| Atrial fibrillation | Gencer et al., 2021: 7 trials, 81,210 people | 1,25 (1,07 à 1,46) | 25% higher risk (7 to 46%), more above 1 g per day (49% higher). |
| Age-related macular degeneration | AREDS2, 2013: 4,203 people, 5 years | 0,97 (0,82 à 1,16) | 31% of eyes progressed to an advanced form, versus 31% with placebo: no difference. 350 mg of DHA and 650 mg of EPA per day, added to the AREDS vitamin mix. Margin at 98.7%; the calculation counts eyes, not people. |
- humanDoses. VITAL and ASCEND: 1 g per day (460 mg of EPA and 380 mg of DHA). REDUCE-IT and STRENGTH: 4 g per day (NIH).
- humanThe placebos. REDUCE-IT used a mineral oil, considered not neutral; STRENGTH, corn oil (NIH). This is one possible explanation for the gap between these two trials.
- humanAtrial fibrillation. 7 trials combined: 25% higher risk; more than 1 g per day: 49% higher; 1 g or less: 12% higher; about 11% higher per added gram (Gencer et al., 2021). In REDUCE-IT: 3.1% hospitalized for atrial fibrillation versus 2.1% (Bhatt et al., 2019).
- hypothesisHow to read it. A hazard ratio of 0.75 means 25% fewer events than with placebo during the trial; the margin is the 95% confidence interval.
With care: this page explains, it does not replace medical advice. High-dose omega-3 supplements can slightly raise the risk of atrial fibrillation, and could lengthen clotting time with some anticoagulants: if you take medication, talk to your doctor or pharmacist.
Frequently asked questions about omega-3s
Can the body make its own omega-3s?
Not ALA: it must come from the plate, like linoleic acid for omega-6s (NIH). The liver can lengthen ALA into EPA and then DHA, but very little: generally less than 15% according to the NIH, up to 21% into EPA in young women in a small study, and almost no DHA in young men (Burdge et al., 2002).
Are omega-3s from seeds as good as those from fish?
They are not the same. Flaxseeds, chia seeds and walnuts provide ALA; oily fish provide EPA and DHA, first made by microalgae. According to ANSES, the conversion of ALA into DHA is too low to cover DHA needs.
How much omega-3 is needed per day?
For ALA, 1.1 g per day for women and 1.6 g for men (NIH). In France, ANSES sets 250 mg of EPA and 250 mg of DHA per day for adults. For comparison, 85 g of cooked farmed Atlantic salmon provides 1.24 g of DHA and 0.59 g of EPA (NIH).
Do omega-3 supplements protect the heart?
The results differ. At 1 g per day, VITAL and ASCEND show no clear difference across all cardiovascular events. At 4 g per day, REDUCE-IT finds 25% fewer events with purified EPA, but STRENGTH finds nothing with EPA and DHA. At high doses, the risk of atrial fibrillation rises (Gencer et al., 2021).
What is the Omega-3 Index?
It is the share of EPA and DHA among the fats in the red blood cell membrane. It reflects roughly the last 120 days. It is often 3 to 5% in the West and about double in Japan (NIH).
See also
Where do the fats we eat go? Why doesn't Lp(a) go down with diet? Where does magnesium go in the body?
Sources
- Office of Dietary Supplements (NIH). Omega-3 Fatty Acids: fact sheet for health professionals, updated August 22, 2025. ods.od.nih.gov
- ANSES. Les acides gras oméga 3, 2025. anses.fr
- ANSES. Les lipides, 2021. anses.fr
- Burdge GC, Wootton SA. Conversion of alpha-linolenic acid to eicosapentaenoic, docosapentaenoic and docosahexaenoic acids in young women. British Journal of Nutrition, 2002. doi:10.1079/BJN2002689
- Burdge GC, Jones AE, Wootton SA. Eicosapentaenoic and docosapentaenoic acids are the principal products of alpha-linolenic acid metabolism in young men. British Journal of Nutrition, 2002. doi:10.1079/BJN2002662
- Emken EA, Adlof RO, Gulley RM. Dietary linoleic acid influences desaturation and acylation of deuterium-labeled linoleic and linolenic acids in young adult males. Biochimica et Biophysica Acta, 1994. doi:10.1016/0005-2760(94)00054-9
- Nguyen LN et al. Mfsd2a is a transporter for the essential omega-3 fatty acid docosahexaenoic acid. Nature, 2014. doi:10.1038/nature13241
- Umhau JC et al. Imaging incorporation of circulating docosahexaenoic acid into the human brain using positron emission tomography. Journal of Lipid Research, 2009. PMC2694326
- SanGiovanni JP, Chew EY. The role of omega-3 long-chain polyunsaturated fatty acids in health and disease of the retina. Progress in Retinal and Eye Research, 2005. doi:10.1016/j.preteyeres.2004.06.002
- Calder PC. Docosahexaenoic Acid. Annals of Nutrition and Metabolism, 2016. doi:10.1159/000448262
- Harris WS, von Schacky C. The Omega-3 Index: a new risk factor for death from coronary heart disease? Preventive Medicine, 2004. doi:10.1016/j.ypmed.2004.02.030
- Manson JE et al. Marine n-3 Fatty Acids and Prevention of Cardiovascular Disease and Cancer. New England Journal of Medicine, 2019. doi:10.1056/NEJMoa1811403
- ASCEND Study Collaborative Group, Bowman L et al. Effects of n-3 Fatty Acid Supplements in Diabetes Mellitus. New England Journal of Medicine, 2018. doi:10.1056/NEJMoa1804989
- Bhatt DL et al. Cardiovascular Risk Reduction with Icosapent Ethyl for Hypertriglyceridemia. New England Journal of Medicine, 2019. doi:10.1056/NEJMoa1812792
- Nicholls SJ et al. Effect of High-Dose Omega-3 Fatty Acids vs Corn Oil on Major Adverse Cardiovascular Events in Patients at High Cardiovascular Risk: The STRENGTH Randomized Clinical Trial. JAMA, 2020. doi:10.1001/jama.2020.22258
- Afssa. Avis relatif à l'actualisation des apports nutritionnels conseillés pour les acides gras (saisine 2006-SA-0359), 2010. anses.fr
- Schuchardt JP et al. Red blood cell fatty acid patterns from 7 countries: focus on the Omega-3 index. Prostaglandins, Leukotrienes and Essential Fatty Acids, 2022. doi:10.1016/j.plefa.2022.102418
- Age-Related Eye Disease Study 2 Research Group. Lutein + zeaxanthin and omega-3 fatty acids for age-related macular degeneration: the AREDS2 randomized clinical trial. JAMA, 2013. doi:10.1001/jama.2013.4997
- Gencer B et al. Effect of Long-Term Marine Omega-3 Fatty Acids Supplementation on the Risk of Atrial Fibrillation in Randomized Controlled Trials of Cardiovascular Outcomes: A Systematic Review and Meta-Analysis. Circulation, 2021. doi:10.1161/CIRCULATIONAHA.121.055654
True or false?
Flaxseeds provide DHA.
False. They provide ALA. The liver turns very little of it into DHA: 0 to 9% depending on the study (Burdge and Wootton, 2002; Emken et al., 1994).
The brain makes its own DHA.
False. It cannot make it: it brings it in from the blood through a gate, Mfsd2a, in the walls of its vessels (Nguyen et al., 2014, in mice).
At high doses, omega-3 supplements raise the risk of atrial fibrillation.
True. Above 1 g per day, the risk was 49% higher than with a placebo across 7 combined trials (Gencer et al., 2021).
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Metabolive. "Where do omega-3s go in the body?" Updated November 2, 2026. https://metabolive.com/en/everyday/omega-3.