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.

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 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 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.

Elderly people with memory problems who eat more fish oil-like fats (DHA and EPA) tend to have less damage from harmful molecules in their blood, which might help protect their brains.

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.