GPBAR1 and obesity due to melanocortin 4 receptor deficiency: Gpbar1−/− mice (TGR5) have a ~25% decrease in bile acid pool size but gain weight at the same rate or slightly more rapidly than wild‐type mice on both standard chow and high‐fat diets (Maruyama et al. 2006), indicating that this relatively small change in bile acid does not prevent diet‐induced obesity.