Roux-En-Y Gastric Bypass (RYGB) and Sleeve Gastrectomy (SG) are now both recognised as the most effective treatment options for morbid obesity and its related comorbidities. However, despite similar long-term outcomes, their precise mechanisms of action are yet to be fully understood.


28 patients were included in this prospective study. 17 underwent RYGB and 11 underwent SG. 24-hour urine samples were collected pre-operatively and at 3-months post-operatively. These underwent untargeted metabolic profiling using ultrahigh-performance liquid chromatography tandem mass spectrometry with electrospray ionization method (UHPLC-ESI-MS/MS).


Multivariate paired data analysis was performed. We found Kynurenic acid to be a statistically significant differentiator when comparing the post-operative urinary metabolome of those who have undergone RYGB and SG. Those who underwent RYGB had a 1.37-fold decrease at 3 months when compared to pre-operative baseline and those who underwent SG had a 1.04-fold increase.


Kynurenic acid is a metabolite found within the tryptophan essential amino acid metabolic pathway. It has documented correlation with obesity, satiety and Type 2 diabetes. This finding points towards a possible mechanism of action differences when comparing RYGB and SG. Other metabolites within this pathway should be further investigated.