Association of Diet- and Health-Related Beliefs with Restrictive Diets Without Medical Indication in a Self-Selected Online Sample of Adults in Romania: A Cross-Sectional Study

Background: The adoption of restrictive diets without medical indication is increasing, but the cognitive factors associated with this dietary behavior remain insufficiently understood. The aim of this study was to examine the proportion of participants following restrictive diets in a self-selected online sample of adults living in Romania and to analyze the associations of nutrition knowledge, beliefs regarding the relationship between diet and health, food vigilance, and social media use with the adoption of restrictive diets without medical indication. Methods: This cross-sectional observational study was conducted online in a self-selected sample of 766 adults living in Romania. Participants were classified into three groups: no restrictive diet, medically indicated restrictive diet, and restrictive diet without medical indication. Three composite scores were constructed: Restrictive Health Beliefs, Food Vigilance, and Nutrition Knowledge. Differences between groups were assessed using non-parametric tests and χ2 tests, and factors associated with the adoption of restrictive diets were analyzed using multinomial logistic regression and multiple linear regression. Results: Among the participants, 30.9% reported following a restrictive diet, and 13.1% adopted one without medical indication. Participants who followed restrictive diets scored higher for Restrictive Health Beliefs and Food Vigilance but not Nutrition Knowledge. In the multivariate analysis, Restrictive Health Beliefs showed the strongest independent association with restrictive diets without medical indication. Food Vigilance was only associated with medically indicated restrictive diets (p < 0.001), suggesting an adaptive role in a therapeutic context. Nutrition knowledge and social media use were not independently associated with restrictive diets without medical indication, although social media use was associated with higher levels of Restrictive Health Beliefs. Conclusions: The results suggest that the adoption of restrictive diets without medical indication is more closely associated with beliefs regarding the relationship between diet and health than with the level of nutrition knowledge. These findings support the development of nutrition education interventions that, in addition to conveying evidence-based information, promote the development of critical thinking and the correction of insufficiently scientifically substantiated dietary beliefs.