A weight management system comprises a cash register (CRS), a user client (UC) and a weight management module (WM), coupled via a wide area network (WAN). A user has a personal card (PC) with a code, the code identifying the user to the cash register and being related to a user ID. The cash register system (CRS) is arranged for sending, when the user pays the food item, corresponding food intake information and the user ID to the weight management module (WM). The weight management module (WM) comprises a food information system, a calorie intake component and a calorie balance component. The food information system stores a respective calorie content for a plurality of food items. The calorie intake component is coupled to the food information system and calculates an amount of calories taken by the user based on the received food intake information.