In the last decades the proportion of processed, ready-to-eat food in total food consumption has increased, whereas the amount of homemade meals prepared from basic food has decreased. The objective of this thesis was to assess the effect of food processing on dietary quality of children, adolescents and adults. The investigation was based on food record data from three nutrition surveys (VELS, EsKiMo, NVS II, n = 2.985). A database was created to classify the consumed food based on their processing state. For this purpose a newly developed classification system was used. The dietary quality was negatively affected by large amounts of highly processed foods: lower proportion of fruits and vegetable, higher proportion of sausage products, sweets and sugar-sweetened beverages, a higher energy density, a lower nutrient density, a higher supply of food additives (qualitative) as well as, in particular, a higher risk for the overweight in childhood. Recommendations for the food industry are to produce products that are nutritionally well-balanced by changing recipes, the process of production and basic food. Consumers are advised to change the proportions of daily food consumption in order to increase the amount of fresh food and to reduce the portion of processed food.