The BBC News Health website recently reported that a diet rich in vitamins and fish may protect the brain from ageing while junk food has the opposite effect, research suggests.
Elderly people with high blood levels of vitamins and omega 3 fatty acids had less brain shrinkage and better mental performance, a Neurology study found.
Trans fats found in fast foods were linked to lower scores in tests and more shrinkage typical of Alzheimer's.
A UK medical charity has called for more work into diet and dementia risk.
The best current advice is to eat a balanced diet with plenty of fruit and vegetables, not smoke, take regular exercise and keep blood pressure and cholesterol in check, said Alzheimer's Research UK.
"There is a clear need for conclusive evidence about the effect of diet on our risk of Alzheimer's, which can only come from large-scale, long-term studies?
The research looked at nutrients in blood, rather than relying on questionnaires to assess a person's diet.
Read more at BBC News Health