Dietary Sources of Glycine Betaine and Proline Betaine in Plant Foods and Their Potential Biological Relevance in Human Nutrition

Betaines are natural nitrogen-containing compounds widely distributed in plant-derived foods and animal tissues, where they function primarily as osmolytes, chaperons, and methyl donors. As such, they have attracted increasing interest as dietary components and metabolic biomarkers in human nutrition. This study provides a comparative characterization of glycine betaine (GlyBet) and proline betaine (ProBet) by combining targeted LC–MS quantification in a representative selection of plant-based foods with complementary in silico analyses and integration of dietary intake estimates derived from published nutritional and metabolomic studies, together with human metabolomic data. A validated HPLC–ESI–MS method was applied to quantify GlyBet and ProBet across cereals, pseudocereals, vegetables, and fruits. GlyBet was found to be predominantly abundant in leafy vegetables and in several cereal and pseudocereal flours, whereas ProBet was highly enriched in citrus fruits, particularly bergamot, chinotto, and bitter orange. In silico ADMET predictions were used to provide a qualitative and comparative description of the pharmacokinetic and safety-related properties of the two betaines, indicating broadly similar hydrophilic profiles with modest differences in solubility, clearance, and predicted skin sensitization. Similarity-based target prediction analyses, used in an exploratory framework, suggest distinct contextual tendencies for the two betaines. GlyBet is primarily associated with pathways related to one-carbon metabolism and cellular stress responses, whereas ProBet shows a closer contextual association with signaling-related processes. By integrating experimental data, computational analyses, and human metabolomic information, this work supports the interpretation of betaines as biomarkers of dietary intake and systemic metabolic status.