While a number of studies have explored consumer attitudes and behaviors towards green brands, the importance of green brand image for mainstream brands is less well understood. This study seeks to explore if the green image of mainstream fast food brands influences consumer loyalty and how their attitudes towards and knowledge of environmental issues may affect perceptions of the environmental performance of fast food brands. Using data gathered from a convenience sample of 2001 Gen Y and Gen Z consumers in France, our study establishes a critical linkage between consumers' environmental values and brand loyalty by including green brand image as a mediator. Further, by exploring mainstream brands, rather than brands that are positioned primarily on green attributes, we find that the mediating effect of green brand image may be dependent on the brand positioning.