Bariatric surgery is the most effective treatment for obesity, producing massive and durable weight loss. One anastomosis gastric bypass (OAGB) is a restrictive and malabsorptive procedure that is rapidly gaining in popularity; it is simpler technically than other common procedures and has a low rate of complications. OAGB has similar, if not better, weight loss results than Roux-en-Y gastric bypass and biliopancreatic diversion, likely because of the exclusion of a longer biliopancreatic limb. In addition to weight loss, OAGB has been shown to improve many of the commonest metabolic abnormalities associated with obesity such as insulin resistance. Recent studies using traditional analytical techniques, however also more advanced metabolomics techniques, provide important insights into the potential mechanisms for the physiological effects of OAGB, including improved lipid profile (normalization of triacylglycerol and cholesterol levels), reduced concentrations of total free fatty acids however increased branched-chain fatty acids, decreased branched-chain amino acid levels, and increased circulating bile acids. All these changes likely contribute to improved glucose homeostasis and cardiometabolic health.