For older people who don't have a specific gene variant called APOE ε4, eating fish or omega-3s from food doesn't seem to help slow down memory loss or brain aging over about five years.

For older people who carry a specific gene variant called APOE ε4, eating more of a plant-based omega-3 fat called ALA might help their brain slow down its decline, but this benefit seems small and may disappear when you account for heart health factors.

Eating seafood at least once a week might help older adults with a specific gene variant keep their memory and thinking skills sharper for longer, compared to those who don't eat seafood as often.

For older people who carry a specific gene variant called APOE ε4, eating moderate amounts of fish or other foods rich in omega-3s might help them remember things and think clearly a bit longer — but eating even more doesn’t help any more, and might not help at all.

Eating more fish or having more omega-3 fatty acids in your body doesn't seem to help your brain work better if you're an older adult who's already thinking clearly.

When older adults with memory problems eat more omega-3 fats from fish or supplements, their bodies show less of a type of cell damage linked to aging and brain decline.