"Increasing rates of highly malignant hepatocellular carcinoma (HCC) and biliary tract cancers (GBTC) observed in Western populations may be related to obesogenic lifestyle factors and their metabolic consequences, such as metabolic syndrome (MetS), inflammation and altered production of bile acids (BA). Such lifestyle behaviours may induce changes in the gut microflora which in turn affect BA profiles, increasing their carcinogenicity. Some elevated BA may be oncogenic in exposed liver, bile ducts and gall bladder. Data from case-control studies show higher blood BA in patients with various liver diseases, but from these designs it is unclear if the differences in BA levels are etiologic or consequential. To date no prospective studies have investigated the role of circulating BA levels in the development of HCC/GBTC, nor any potential interactions with diet, obesity and MetS. Interestingly, Vertical Sleeve Gastrectomy (VSG), an anti-obesity intervention, may alter BA profiles in some patients towards a potentially detrimental composition, but this is largely unexplored.