BACKGROUND: Sustainable nutrition is based on foods with a low environmental impact, accessible and affordable, ensuring protection of the biodiversity, while including the cultural elements of each geographical region. The present cross-sectional study aimed to evaluate adherence to a sustainable diet and the perceived environmental benefit of adopting a sustainable diet among adults in Greece. METHODS: The Sustainable HEalthy Diet (SHED) questionnaire evaluated sustainable nutrition practices and awareness in a sample of 607 adult Greeks recruited through social media. RESULTS: A positive association was revealed between healthy eating, a plant-based diet and organic awareness. Healthy eating was related to the consumption of low-salt and low-sugar products, avoiding added salt and ultra-processed foods (UPFs), as well as limiting sweets and soft drinks. Most participants (94.6%) were flexitarians, consuming meat instead of plant-based foods, although showing a preference for legumes over meat products. Most (86.8%) failed to meet the 5-a-day recommendations for fruit and vegetables, which were bought mainly from supermarket chains, with men resolving to electronic commerce purchases, while women preferring small, local grocery shops. Most responders consumed tap water (54.9%) and homemade meals daily (75.0%). Many participants (32.8%) reported separating and recycling food scraps at home, using neighborhood composters. When organic produce was selected, this involved mainly fruits and vegetables. Between men and women, the latter adopted a plant-based diet to a greater extent, consumed fewer soft drinks, were keener to consume local produce, limit meat intake and eat crops that are pesticide- and herbicide-free. Overall, Greek consumers show preference to local products. Most of them fail to compost and cut down on meat intake. The tool's internal consistency measured by Cronbach alpha was 0.702 and 0.736 for the healthy eating and sustainable eating domains respectively, 0.798 for the environmental domain, while the other domains had lower scores due to contradictory questions. Our Confirmatory Factor Analysis (CFA) demonstrated a good fit (CFI = 0.896, TLI = 0.87) with strong positive relationships between healthy eating, a plant-based diet and organic awareness. CONCLUSIONS: The results indicate that adult Greeks more easily implement some aspects of sustainable nutrition (organic, local foods), while others appear more difficult (compost, reduce meat intake). Nonetheless, the results can be useful in designing interventions to increase dietary sustainability awareness among Greeks, including educational programs and improved infrastructures.