Background/Objectives: Traditional dietary screeners face significant limitations: they rely on subjective self-reporting, average intake estimates, and are influenced by a participant’s awareness of being ob-served—each of which can distort results. These factors reduce both accuracy and reproducibil-ity. The Guide Against Age-Related Disease (GARD) addresses these issues by applying Assem-bly Theory to objectively quantify food and food behavior (FFB) complexity. This study aimed to validate GARD as a structured, bias-resistant tool for dietary assessment in clinical and re-search settings. Methods: The GARD survey was administered in an internal medicine clinic within a suburban hospital system in the southeastern U.S. The tool assessed six daily eating windows, scoring high-complexity FFBs (e.g., fresh plants, social eating, fasting) as +1 and low-complexity FFBs (e.g., ultra-processed foods, refined ingredients, distracted eating) as –1. To minimize bias, pa-tients were unaware of scoring criteria and reported only what they ate the previous day, avoid-ing broad averages. A computer algorithm then scored responses based on complexity, inde-pendent of dietary guidelines. Internal (face, convergent, and discriminant) and external validity were assessed using Spearman rho correlations. Results: Face validation showed high inter-rater agreement using predefined Assembly Index (Ai) and copy number (Ni) thresholds. Positive correlations were found between high-complexity diets and behaviors (rho = .533–.565, p < .001), while opposing constructs showed moderate negative correlations (rho = –.363 to –.425, p < .05). GARD scores aligned with established diet patterns: Mediterranean diets averaged +22; fast food diets averaged –10.