The aim was to explore the role of consumers' nutrition knowledge while selecting foods for weight management and the predominating food selection factors by combining quantitative and qualitative methodology in a real-life setting during two consecutive shopping tasks given in a supermarket. Thirty-six consumers were given a list of 11 products and asked to think-aloud while selecting (i) a product they usually buy and (ii) a product they use for weight management. After the consecutive shopping tasks, the subjects were interviewed and asked to answer a nutrition knowledge questionnaire. The subjects were categorized by the difference in the energy contents of their selections and the food selection criteria. The energy contents of the selections for weight management were reduced by 10-46%. Ten subjects with the greatest difference between the energy contents of their selections had higher level in nutrition knowledge and mentioned less nutritional issues during the selections than ten subjects with the smallest such differences. Taste was an important product selection criterion by the former group, while the latter focused primarily on price. Nutrition knowledge is interrelated with personal factors and selection goals. It is not necessarily utilized consistently when selecting food products.