Background/Objectives: Plant-based dietary patterns like the Dietary Approaches to Stop Hypertension (DASH) reduce cardiovascular risk, which is a leading cause of mortality globally and in Spain. Diet is also a major environmental determinant, highlighting the need to evaluate public health alongside environmental sustainability. The aim of this study was to analyze the evolution of adherence to the DASH dietary pattern in Spain between 2006 and 2023 and evaluate its relationship with environmental sustainability indicators. Methods: This was an ecological epidemiological study. Food consumption data were harmonized into daily servings to calculate annual DASH scores using a standard 80-point methodology. Environmental impact was assessed by calculating the comprehensive Ecological Footprint (EF) using the Agribalyse^® 3.2 database. The study utilized open data from the Spanish Household Budget Surveys, capturing the consumption habits of approximately 24,000 randomly selected Spanish households annually from 2006 to 2023. The primary measures evaluated were the annual DASH adherence index score and the overall environmental Ecological Footprint. Temporal trends were evaluated using segmented regression models selected via the Akaike Information Criterion and Davies test. Pareto analysis determined individual food group environmental contributions, and correlations assessed the relationship between DASH scores and the EF. Results: DASH adherence increased by 8.26% over the study period, peaking in 2020. The EF demonstrated an overall decrease over time, largely driven by reduced consumption of meat, fish, and eggs. A strong inverse correlation was found between the DASH score and the EF (r = −0.8237 (95% CI: −0.932 to −0.580; p < 0.001)). Conclusions: A shift toward the DASH dietary pattern in Spain demonstrates potentially convergent health and environmental associations, promoting population cardiovascular health potential while simultaneously mitigating environmental impacts.