This study aimed to investigate the relationship between sustainability and food, and other possible associations with the socio-demographic characteristics and consumer segmentation, as well as to identify the characteristics of sustainable and unsustainable foods and the sustainable diet concept from a consumer perspective. One hundred and fifty consumers responded a questionnaire with word association, free listing, and sentence completion tasks. A thematic analysis was used to analyze the terms. Sustainability and food were associated with the categories health, food of plant origin, and organic food. Healthy was considered the main characteristic of a sustainable food and degradation to the environment was the characteristic of unsustainable food. Regarding the sustainable diet concept, the terms healthy diet and sustainable production stood out. Individuals of higher educational level associated food and sustainability with natural resource preservation and reuse, while individuals with lower educational levels reported the association with healthy food, nutrition, and food of plant origin. The present findings can help designing strategies to integrate food and nutrition education and formulation of public policies, as well as identifying the target market and understanding how the product or service can meet the consumer's needs.