A transition towards sustainable diets ensuring food security while preserving ecosystems is necessary, but remains challenging. Low-income consumers, particularly those experiencing food insecurity, require specific consideration since they face financial constraints when making food choices, leading to poorer diets. However, little is known about the place given to sustainability in their choices. This study thus aims to identify the role played by sustainability in the food values of food-insecure consumers in France. Twenty-nine semi-structured interviews with users of a social grocery store were conducted to investigate food values and actual behaviours, with a focus on the four dimensions of sustainable diets - health, economic, sociocultural and environmental. Verbatims were analysed through thematic analysis. Five core values were identified, namely health and nutrition, naturalness, trust and control, solidarity and frugality, and preferences. Participants valued all dimensions of food sustainability but notably valued less the environmental dimension. Despite various strategies, participants felt unable to adhere to their values in practice, mainly because of their socioeconomic vulnerability. They insisted on their lack of control over their food behaviour. These findings provide insights into the disempowerment experienced by consumers with low financial resources regarding more sustainable food choices. Our study calls for interventions addressing affordability issues and considering consumers' food values, while providing opportunities to make consumers feel involved in the transition of the food system.