The three main omega-3s are ALA (alpha-linolenic acid, found in flaxseed, chia, walnuts, canola oil), EPA and DHA (found in oily fish — salmon, mackerel, sardines, herring — and algae). ALA is essential (the body cannot make it); conversion of ALA to EPA and DHA is inefficient (< 10%), so direct sources of EPA/DHA are nutritionally important.
The strongest evidence for omega-3s is in cardiovascular disease prevention — high-dose EPA supplements (icosapentaenoic acid) have demonstrated significant reductions in cardiovascular events in people with elevated triglycerides, though not all omega-3 supplements show this effect. Oily fish consumption is consistently associated with lower cardiovascular mortality in observational research.
For most adults, two portions of oily fish per week (≈250–500 mg EPA/DHA per day) is a practical target. Algae-based DHA/EPA supplements are a viable alternative for those who avoid fish.