Today vegetarian nutrition is more accepted and widespread in Europe than in former years. For a long time scientific research on vegetarian diets has focused mostly on malnutrition, whereas nowadays research centers increasingly on the preventive potential of plant-based diets. We followed a nutritive and a metabolic-epidemiological approach to obtain dietary recommendations. A MEDLINE research was performed for all plant food groups relevant for a vegetarian diet (key words: all relevant food groups, "vegetarian diet", "chronic disease", "cancer", "cardiovascular disease", "diabetes mellitus", "osteoporosis"). All relevant food groups were characterized regarding their nutrient content and rated with respect to the available metabolic-epidemiological evidence. Based on the evidence criteria of the WHO/FAO, cancer risk reduction by a high intake of vegetables and fruits is assessed as probable or possible, while a lowered risk of cardiovascular disease is convincing and a lowered risk of osteoporosis is probable. The evidence of a risk reducing effect of whole grain relating to colorectal cancer is assessed as possible, whereas it is probable relating to cardiovascular disease and diabetes mellitus type 2. There is an insufficient risk-reducing effect of legumes like soja relating to epithelial tumours and cardiovascular disease. The evidence of a risk-reducing effect of nuts to cardiovascular disease is assessed as probable, and in relation to cholelithiasis and diabetes mellitus type 2 as possible and insufficient, respectively. In conclusion, high consumption of fruits, vegetables, whole grains and nuts can lower the risk for several chronic diseases.