While the nutritional quality and environmental impact of diets are widely assessed, different production modes (organic vs. conventional) remain understudied as for sustainability. The present study examines the associations between different dimensions of sustainability of food purchases and sociodemographic factors. Households (n = 462) were included in this cross-sectional study using quota sampling in Montpellier Metropolitan Area. Food items acquired over one month were registered in a food supply diary, and the expenditure share of each food group (including organic food) was estimated. Validated indexes estimated scores reflecting the nutritional quality and the environmental impact of food purchases according to these expenditure shares. Associations were tested for each sustainability dimension using linear and multinomial logistic regression models adjusted for sociodemographic factors (e.g. age, education, living area). The age of the household's reference person was consistently related to the sustainability dimensions of food purchases, albeit in different ways. While older age was associated with better nutritional quality (estimate for age >50 years vs. age between 30-50 [95%CI]=0.91[0.29;1.54]), it was associated with a higher environmental impact (estimate for age >50 years vs. age between 30-50 [95%CI]=1.84[0.95;2.73]). Households with a highly educated reference person (OR master's degree vs. lower education levels [95%CI]=1.59 [1.02;2.47] had a larger share of organic foods and those living around the city of Montpellier (OR vs. living in the city centre [95%CI]=0.44[0.24;0.81]) had a smaller share. Our findings highlight that sociodemographic factors relate to sustainability dimensions in different ways. In addition, we address organic food purchases, which provide insights into different aspects of sustainability. Taken together, the findings suggest that there are various levers for promoting healthy and sustainable diets at the consumer level. Key messages • Sustainability of food purchases relates to sociodemographic factors (i.e. age, education, and living location); different dimensions may be addressed. • Mode of food production (i.e., organic) may provide insights in the context of sustainable diets.