Age-associated cognitive decline and dementia are conditions in which there is deterioration in memory, thinking, and behavior, with profound effects on the ability to perform everyday activities and well-being. Even if dementia mainly affects older persons, it is not a normal part of aging. Alzheimer's disease accounts for 60–75% of dementia cases. The number of persons affected will increase in the next decades in parallel with aging of the world population. Hence, unless some approach is found to reduce age-related deterioration of cognitive functions, health care costs will continue to rise exponentially. There is a wealth of epidemiological evidence supporting a relationship between diet and Alzheimer's disease, and suggesting that the risk of cognitive decline may be reduced by dietary interventions. It has been proposed that adopting a healthy diet and lifestyle that improves cardiovascular function may help delaying the onset of Alzheimer's disease due to its potential association with vascular disease. Several nutrients, dietary components, supplements and dietary patterns have been reported in relation to their association with cognition and with the development of cognitive decline and Alzheimer’s disease. The possible effect of diet on the prevention of dementia is of tremendous scientific and general interest, because hitherto there is no definitive evidence of any effective pharmacological treatment for dementia. The aim of this review is to evaluate the evidence for the effects of some dietary components, supplements, and dietary patterns as neuroprotective, with potential to delay cognitive decline and the onset of dementia.