The phenomenon of population aging is not only associated with an increase in the number and proportion of older people in society, but also with an increase in the incidence of cognitive impairment. This can impair the functioning of the elderly in everyday life, work and social life participation and impair their quality of life. Hence, it is important to identify the protective factors. Neurodegenerative changes are closely linked to inflammatory processes and oxidative stress. Diet is of great importance, with particular attention being paid to the adequate intake of fruits and vegetables, due to their proven health benefits. This may be correlated to the protective effect of the bioactive substances that are present in fruits and vegetables, in particular flavonoids and carotenoids. The elderly who consume 5 servings a day of fruits and vegetables have a higher antioxidant capacity of blood serum, while the risk of chronic diseases, including neurodegenerative and mortality rates are lower. The analysis included the results of 16 published epidemiological studies, including people aged 65+. Their results are discussed in 4 fields of the effects on cognitive function (1) fruit and vegetable intake; (2) flavonoids intake; (3) carotenoid nutritional status; (4) mechanism of action of plant bioactive substances. It has been found that the positive effects of consumption of fruits and vegetables may be associated with cognitive functions in the three possible areas, ie.: (1) improvement in cognitive testing; (2) delaying or preventing age-related deterioration of cognitive decline; (3) reducing the risk of neurodegenerative diseases.