For years, predictions concerning the epidemiology of dementia, particularly Alzheimer’s disease, have been sinister. The commonness of dementia at present and prognoses saying that the number of demented patients will triple in the next decades prompts the search for effective treatment methods. Unfortunately, despite long studies, no effective therapy for neurodegenerative syndromes has been developed. Therefore, simultaneously conducted studies aim at establishing effective prevention. Apart from physical and mental activity, diet is another field explored in the preventive investigations. More and more correlations between nutritional status, diet and cognitive functions are observed. The investigations in this area may be divided into three basic fields. First, basic examinations are used to analyse the impact of nutrients on the functioning of the nervous system. Second, there are ongoing observation projects and population-based studies. A long observation of behaviours and nutritional habits in large cohorts as well as rates indicating compliance to given dietary guidelines enable researchers to draw conclusions concerning protective effects of diet. Third, it is attempted to conduct prospective preventive studies (with dietary interventions and recommendations concerning mental and physical activity) as well as clinical trials evaluating the effects of specific diets or impact of some food products (e.g. foods for special medical purposes). The current knowledge suggests that dietary interventions, particularly when combined with physical and mental activity, may be the most advantageous if implemented early enough and observed nearly for the entire life.