The Effect of Dietary Lemon Intake on Organic Acids in Morning Urine

This study aimed to investigate changes in organic acid metabolites in morning urine induced by dietary lemon intake and to explore the relationship between these metabolites and associated metabolic pathways. Fourteen healthy volunteers were prospectively recruited and divided into two sequential phases: a 10-day baseline phase and a 10-day lemon intake phase. First-morning urine samples were collected. Gas chromatography-mass spectrometry (GC-MS) was used to analyze organic acid levels. Differential metabolites were identified through multivariate analysis and paired t tests, and functional enrichment analysis was performed to map metabolic pathways. Ten organic acid metabolites exhibited significant changes (p < 0.05) after lemon intake. Differential metabolites, including citric acid, lactic acid-2, 2-hydroxymethyl-butyric acid-2, phenylacetic acid-1, and uracil-2, were primarily enriched in pathways such as the citrate cycle (TCA cycle), glyoxylate and dicarboxylate metabolism, pyrimidine metabolism, tyrosine metabolism, and fatty acid biosynthesis. Dietary lemon intake increased the concentrations of energy metabolites (citric acid) and saturated fatty acids (palmitic acid-1), while decreasing the concentrations of organic bases (uracil-2) and catecholamine metabolites (vanillylmandelic acid-3 [VMA]). These findings suggest that lemon consumption may influence metabolic pathways linked to renal, oncological, and neurological diseases, providing insights for dietary interventions in disease prevention.