I rememberd reading on Stephen Guyenet's blog here about how weight loss surgery has no effect on those poor people with Melanocortin 4 receptor ( MC4R ) mutations, the link that Stephen gives in his blog is to a study that that looked at gastric banding surgery, which is actually significantly different from Roux-en-Y surgery.
In Roux-en-Y surgery, the ileum l-cell rich part of the intestine is moved right next to the entrance of the new stomach, but also, bile acids secreted from the gall bladder are given direct access to the rest of the ileum, which seems to cause hypersecretion of GLP-1 and results in intense stimulation of the POMC neurons.
I recently came across this study here that suggests that in actuality, even those people with MC4R receptor mutations may benefit from surgery aslong as it is Roux-en-Y.
I think this could be one of the strongest arguments yet for the power that incretins and bile acids play in bodyfat balance. Is it so powerful that it can even go someway as to help alleviate some the dreaded MC4R mutation effect of morbid obesity?