Strong evidence suggests that older adults at risk of cognitive decline benefit from healthy lifestyle strategies to prevent or delay cognitive disorders. In particular, nutrition has been shown to preserve cognitive functions. Nutritional interventions, whether with single nutrients or following dietary patterns, have all shown protective effects against cognitive decline. In particular, higher levels of vitamins C, D, E, K, and the B family were associated with a better cognitive status. Likewise, fruit and vegetable consumption and omega-3 intake were protective against declined cognition. Regarding dietary patterns, the Mediterranean-type diet, DASH, and MIND diets are all positively associated with slower rates of cognitive decline and decreased risk of incident Alzheimer’s disease and dementia. Nevertheless, intervention trials with vitamins or omega-3 supplements have not demonstrated conclusive evidence for preventing cognitive decline in healthy older adults, or for preventing loss or restoring function in patients with mild to moderate decline. Nutritional recommendations for older adults should emphasize dietary intakes of nutrients and food groups following those recommendations, as well as adoption of the Mediterranean, DASH, or MIND diets, in order to decrease risk of cognitive decline.