What is the difference between ALA, EPA and DHA?

Three fats in one family

All omega-3 fats have a double bond three carbon atoms from the end of their chain. ALA has 18 carbon atoms, EPA has 20 and DHA has 22.^[1] ALA is essential: the body cannot make it, so it must come from food. The same is true of linoleic acid, an omega-6 fat.^[1]

Where each one comes from

• ALA: flaxseed oil has 7.26 g per tablespoon, chia seeds 5.06 g per 28 g, English walnuts 2.57 g per 28 g and canola oil 1.28 g per tablespoon.^[1]
• EPA and DHA: a cooked 85 g serving of farmed Atlantic salmon has 1.24 g of DHA and 0.59 g of EPA. Herring, sardines and mackerel are also rich sources.^[1]
• Algae: microalgae make EPA and DHA, and fish collect them through the food chain.^[1] Algae oils are a vegetarian source of DHA, and some also contain EPA.^[2]

How the body converts ALA

1. The liver turns a small part of ALA into EPA, and then into DHA. Reported rates are below 15%.^[1]
2. ALA and linoleic acid compete for the same enzymes.^[1]
3. In adults on Western diets, extra ALA raises EPA in the blood but has little effect on DHA. Only DHA from food or supplements raises blood DHA well.^[3]

The omega-3 index is the share of EPA and DHA in red blood cells.^[1] A 2022 review of 13 trials found that high doses of flaxseed oil or echium seed oil did not raise it. Algae oil raised it in every study.^[4] For this reason, eating EPA and DHA from food or supplements is the only practical way to raise their levels in the body.^[1]

What each one does

Omega-3 fats are part of the membranes of cells. DHA is especially high in the retina, the brain and sperm.^[1] DHA builds up in the baby's brain and retina fastest in the last 3 months of pregnancy. It keeps building up in the brain for the first 2 years after birth.^[1]

EPA and DHA compete with arachidonic acid, an omega-6 fat, to make signal molecules. More EPA and DHA moves the balance toward less inflammatory activity.^[1] In blood fats they differ: a 2011 review found that both lowered triglycerides, but DHA raised LDL cholesterol by about 7 mg/dL compared with placebo and EPA did not.^[5]

How much people get

Most people in the US get the advised amount of ALA. Women eat about 1.59 g a day and men about 2.06 g.^[1] EPA and DHA from food add only about 90 mg a day in adults.^[1] A lack of omega-3 can cause rough, scaly skin and dermatitis, but this classic deficiency almost never occurs in healthy people in the US.^[1]

Which one the research is about

Most studies of health effects tested EPA and DHA from fish or from supplements such as fish oil, not ALA from plants.^[1]