In this presentation, I will present my work which is about using ubiquitous technologies to develop systems for preventing obesity and chronic diseases related to diet. In recent years, half of the world adults have tried at least once, to control their body weight in order to maintain a fit weight or to lose weight. And, to reach that goal, the most common methods are the practice of physical exercises and the restrictions of intake calorie from meals. For someone to successfully control his/her body weight, it would be important to measure the intake food calorie and adjust it to the amount of expended calorie. However, previous studies have shown that people tend to underestimate calorie from food and overestimate calorie burned from physical activity. In this presentation, I will introduce you the two ubiquitous systems that we developed to help people to estimate (1) the calorie intake from the food they eat and (2) the calorie burned when they exercise. The first system, which is an image-based system, estimates food weight and food calorie from a single picture of the food by using ordinary eating-chopsticks as a measurement reference. The second system recognizes and counts physical exercises via a wearable smart-glove. This system integrates 16 force sensitive resistor (FSR) sensors into wearable fitness gloves to assess physical exercises, by analyzing the time series of the pressure distribution in the hand palms of the user observed during workout sessions.