Purpose of review: Whilst research indicates the positive impact of social support across a number of health domains, including weight management, not all social support is beneficial. Findings: This paper reviews the evidence for both positive and negative social support in the context of behavioural interventions and surgery for obesity. It then presents a new model of negative social support focusing on sabotage (‘active and intentional undermining of another person’s weight goals’), feeding behaviour (‘explicit over feeding of someone when they are not hungry or wishing not to eat’) and collusion (‘passive and benign negative social support to avoid conflict’) which can be conceptualized within the context of relationships as systems and the mechanisms of homeostasis. Summary: There is increasing evidence for the negative impact of social support. This new model could form the basis of further research and the development of interventions for family, friends and partners to maximise weight loss outcomes.