Is GLP-1 increase the main reason Gastric Bypass works so well?

                         This is Jeffrey Sicat's slide from OMA lecture in Washington DC 2015

 Quote from Frank Greenway Review 
May 2015

"Following gastric bypass surgery, levels of ghrelin are extremely low,39 while GLP-1 and PYY are elevated,46 which should attenuate appetite.

These findings raise the possibility that the gastric bypass procedure reduces weight, at least in part, by altering the production and/or release of these mediators of appetite.

Interestingly, among individuals who underwent gastric bypass, plasma ghrelin levels did not oscillate in relation to meals and were much lower than those of normal-weight controls and matched obese controls, after substantial weight loss resulting from a 6-month dietary programme.39 

However, recent studies in rodents have indicated that weight loss following sleeve gastrectomy is not mediated by changes in ghrelin or GLP-1, or through the melanocortin (MC)-4 receptor in the hypothalamus.47, 48, 49

  Instead, as shown by a knockout mouse study, the mechanism of weight loss in sleeve gastrectomy appears to involve the nuclear bile acid receptor, farnesoid X receptor.50

Note that the observation that gut hormones such as ghrelin and GLP-1 are not involved in the mechanism of weight loss with sleeve gastrectomy does not mean that they are not important mediators of body weight. 

Indeed, a rationally designed monomeric peptide has been shown to reduce body weight and diabetic complications in rodents by acting as an agonist at three metabolically related peptide hormone receptors: the GLP-1, gastric inhibitory polypeptide and glucagon receptors.51"

New Peptide in Rodents?