There's a new sign that fish really may be brain food. A study suggests that older people who eat fish at least once a week may cut their risk of Alzheimer's disease by more than half. People 65 and older who had fish once a week had a 60 percent lower risk of Alzheimer's than those who never or rarely ate fish. Meals included tuna sandwiches, fishsticks and shellfish. Amounts eaten were not specified. A researcher says fish is rich in an omega-three fatty acid that is believed to be important for brain development. But she says it's still too soon to be sure fish has properties that can fight Alzheimer's. The researcher is at Chicago's Rush-Presbyterian-St. Luke's Medical Center. The study is in Archives of Neurology.