Performance of GPT-4o combined with retrieval-augmented generation on nutritionist licensing exam questions

GPT-4o, a general-purpose large language model, has a Retrieval-Augmented Variant (GPT-4o-RAG) that can assist in dietary counseling. However, research on its application in this field remains lacking. To bridge this gap, we used the Japanese National Examination for Registered Dietitians as a standardized benchmark for evaluation. Three language models-GPT-4o, GPT-4o-mini, and GPT-4o-RAG-were assessed using 599 publicly available multiple-choice questions from the 2022-2024 national examinations. For each model, we generated answers to each question five times and based our evaluation on these multiple outputs to assess response variability and robustness. A custom pipeline was implemented for GPT-4o-RAG to retrieve guideline-based documents for integration with GPT-generated responses. Accuracy rates, variance, and response consistency were evaluated. Term Frequency-Inverse Document Frequency analysis was conducted to compare word characteristics in correctly and incorrectly answered questions. All three models achieved accuracy rates >60%, the passing threshold. GPT-4o-RAG demonstrated the highest accuracy (83.5% ± 0.3%), followed by GPT-4o (82.1% ± 1.0%), and GPT-4o-mini (70.0% ± 1.4%). While the accuracy improvement of GPT-4o-RAG over GPT-4o was not statistically significant (p = 0.12), it exhibited significantly lower variance and higher response consistency (97.3% vs. 91.2-95.2%, p < 0.001). GPT-4o-RAG outperformed other models in applied and clinical nutrition categories but showed limited performance on numerical questions. Term Frequency-Inverse Document Frequency analysis suggested that incorrect answers were more frequently associated with numerical terms. GPT-4o-RAG improved response consistency and domain-specific performance, suggesting utility in clinical nutrition. However, limitations in numerical reasoning and individualized guidance warrant further development and validation.