Purpose Irritable bowel syndrome is a gastrointestinal disorder which can influence human metabolism. It has been demonstrated that probiotics are beneficial in controlling IBS. Thus, the main objective of the present study was to determine metabolic changes in response to diarrhea predominant irritable bowel syndrome (IBS-D) and to investigate the metabolic effects of a synbiotic intervention on serum, urine, and stool samples from IBS-D patients and healthy controls using proton nuclear magnetic resonance (1HNMR). A 1HNMR-based metabolomics study was conducted on urine and serum metabolites from 16 healthy and eight IBS-D participants at baseline and after 4 weeks of a synbiotic yogurt intervention. At the baseline, serum acetoacetate, myo-inositol, and sarcosine concentrations were higher and threonine and methionine concentrations were lower in the IBS-D cohort than the control group. Moreover, Indoxyl-sulfate concentration of urine was lower and dimethylamine and taurine were higher in the IBS-D group. After intervention, serum concentration of ketone bodies decreased, choline, phenylalanine, and branched-chain amino acids increased in IBS-D group. Metabolomics analysis indicated a shift in one-carbon metabolism. Thus, the level of serum homocysteine was determined and found to be higher in the IBS-D cohort at baseline, and then decreased after the intervention. IBS causes a shift in one-carbon metabolism and these changes can be reversed by a synbiotic intervention. An increase in the number of fecal Lactobacilli and an improvement in the health status of IBS-D patients were also observed in response to intervention.

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