This thesis focuses on a clientele who currently lives with both a lower life expectancy and a lower quality of life due to obesity. The goal of this thesis is to identify and validate effective interventions for people living in a family environment with intellectual disabilities or treated with antipsychotic medication. Methods. Covering a period of five years, this research includes two studies, each lasting two years, evaluating two interventions. The first is a control-group study involving 82 participants. It assesses the effectiveness of interventions aimed at patient self-control and identifies lifestyle factors related to obesity in this population. The second study includes 7 families (comprised of 36 individuals) and 30 public health care professionals. It assesses the effectiveness of interventions, this time targeting the offer of food by the cooks and the support of public health care professionals. Measures : Body mass index (BMI), waist circumference (WC), antipsychotic medication use, family, lifestyle factors (physical activity, consumption of fruits and vegetables, smoking, duration of sleep), survey of food offer and physiological parameters (blood pressure, fasting glucose and lipid). Results. The WC is a more sensitive measure than BMI to detect obesity, particularly in women, who have a higher incidence of abdominal obesity. The family is a determining variable of the variation in the incidence of obesity. The practice of physical activity and the daily consumption of vegetables (excluding potatoes) are associated with less obesity. Interventions aimed at self-control are ineffective with this population. However, interventions aimed at the cooks and the health care professionals are significantly effective in reducing BMI as well as WC and in increasing the frequency of physical activity and consumption of fruits and vegetables, while improving the quality of the food offered. These improvements are maintained after two years. Conclusion. It appears that interventions specifically targeting the cook and involving the health care professionals are an efficient way to help this clientele.This thesis also highlights the usefulness for health care professionals to change from an intervention model of being the"expert", previously used primarily with an institutionalized clientele, to a model of"non-expert" focusing on collaboration, best suited for interventions on lifestyle factors in family environments.