Widespread patterns of poor dietary behavior are a key factor causing the increasing prevalence of chronic diseases around the world. Research provides initial insights into the potential of food literacy (FL) to empower individuals to improve their dietary behavior. Yet, studies on FL interventions in working adults are scarce. This study aimed to investigate the short- and long-term effects of a comprehensive 3-week workplace health promotion program (WHPP) on FL and dietary intake (DI) and to examine the association between FL and DI in a sample of 144 German office workers (30.0% female). Using two random intercept mixed linear regression models, we found significant strong improvements for both FL (β = 0.52, p < .0001) and DI (β = 0.63, p < .0001) after the WHPP when compared to baseline. Significant long-term improvements at 18 months where strong for FL (β = 0.55, p < .0001) and small for DI (β = 0.10, p < .0001). FL showed a significant moderate effect on DI across all measurement time points (β = 0.24, p < .0001). Our study fills a gap of long-term findings in the literature on FL interventions, offers insights into underlying mechanisms, and provides recommendations for effective WHPPs.