Knowledge of Health Benefits of Fruits, Vegetables, and Antioxidants, Propensity to Sustainability and Adherence to the Mediterranean Diet: An Interrelated Evaluation

Background/Objectives: Beyond health benefits, plant-based diets are increasingly recognized for their contribution to environmental sustainability. This study aimed to evaluate knowledge of the health benefits of fruits, vegetables, and antioxidants, adherence to the Mediterranean Diet (MD), and propensity toward sustainable food purchasing in an adult population from Southern Italy, and to explore the relationships among these factors. Methods: A cross-sectional online survey was conducted among 311 adults living in the Campania region. Data were collected on knowledge of fruit and vegetable health benefits, antioxidant knowledge, adherence to the MD assessed using the Medi-Lite score, and attitudes toward sustainable food purchasing. Differences were examined according to gender, age, and educational level. Pearson’s correlation analyses and multiple logistic regression models were used to investigate associations between nutrition knowledge, dietary adherence, and sustainability-related behaviors. Results: Participants showed a medium–high level of knowledge regarding the health benefits of fruits and vegetables, while knowledge of antioxidants was moderate and significantly higher among older adults. Overall adherence to the MD was moderate, with lower consumption of vegetables, legumes, and fish. Most participants reported limited attention to sustainability when purchasing food. Both knowledge of fruit and vegetable health benefits and antioxidant knowledge were positively associated with sustainable food purchasing. In regression analyses, lower nutrition knowledge was independently associated with reduced odds of sustainable purchasing, whereas adherence to the MD was not a significant predictor. Conclusions: Although nutrition knowledge was generally adequate, its translation into sustainable food choices remained limited. These findings support the need for integrated public health strategies to encourage healthier and more environmentally responsible dietary behaviors.