An intervention study by documented dietary counselling was carried out in a sample of 9 children and adolescents (12-15 years) living in a full-time institution in Dortmund. Three weighed dietary records were collected over 3-7 days, one before and one after each of two individual nutrition counselling sessions, which were based on the recommended intake of food groups defined by the Optimized Mixed Diet (OMD), a quantitative preventive dietary conception for children and adolescents. As univariate dietary parameters (e.g., cholesterol intake), which are often used to show the effectiveness of nutrition counselling, do not take into account the multivariate complexitiy of nutrition, we developed 3 multivariate scores to measure the effectiveness of nutrition counselling. They are defined as: Recommended Food group change Score (RFS): Average change in the amounts of the deviations (%) from the reference food groups values (OMD = 100 %) before and after counselling taking into account the aim (eat mor/less) of the counselling session, exclusively based on the food groups addressed during counselling. Total Food group change Score (TFS): Average change in the amounts of the deviations (%) from the reference food group values (OMD = 100 %) before and after counselling based on all food groups consumed. Nutrient Improvement Score (NIS): Average change in the negative deviations (%) of 8 vitamins and 8 minerals from the German reference values for nutrient intake (Deutsche Gesellschaft für Ernährung (DGE) = 100 %) before and after counselling. On average, the intakes of the food groups mentioned during the first counselling session improved considerably (RFS = +36 %), the change in the intake of all food groups was small (TFS = +6 %) and the nutrient intakes did not improve (NIS = 0 %). From the second counselling session the values of the RFS was +10 %, of the TFS was +6% and of the NIS +3 %. This means that the success of counselling on one dietary criterion does not guarantee success on others. Our food and nutrient based scores together with a detailed food intake assessment give an example of multivariate measurements of nutrition counselling outcomes.