This study employs content analysis to explore the representation of Big C (formal, institutional culture) and Small c (informal, everyday culture) cultural elements across different proficiency levels in the “Headway” EFL textbook series. Utilizing the Cultural Content Integration Framework, the study systematically examines how these cultural elements are incorporated to foster intercultural communicative competence (ICC) among learners. The findings reveal a progressive introduction of complex Big C cultural concepts as learners advance, while consistently emphasizing Small c cultural practices, which are crucial for practical communication. Specifically, the second research question reveals that Big C elements, such as Art and Education, gradually increase in frequency at higher proficiency levels, reflecting a pedagogical strategy to expose learners to more abstract cultural concepts as their linguistic capabilities develop. Conversely, Small c elements, including Everyday Living and Interpersonal Relations, dominate across all levels, emphasizing practical cultural knowledge essential for real-world interactions. This balanced approach aligns with the need for sustainable vocabulary teaching methods that integrate both types of cultural content to enhance linguistic proficiency and cultural understanding. The study proposes a sustainable cyclic vocabulary teaching model, which adapts to learners’ evolving needs by reinforcing both Big C and Small c cultural elements through experiential learning activities and continuous assessment. The results underscore the importance of a comprehensive approach to cultural education in EFL, contributing to the development of more culturally responsive teaching practices that prepare learners for real-world intercultural interactions.