Objective: We sought to elucidate further the mechanisms leading to weight loss after gastric bypass (GBP) surgery in morbidly obese individuals. Ghrelin is a gastroenteric appetite-stimulating peptide hormone, fasting levels of which decrease with increasing adiposity and increase with diet-induced weight loss. In addition, ghrelin levels rapidly decline postprandially.
Research methods and procedures: We measured serum ghrelin responses to a 75-g oral glucose tolerance test (OGTT) in 6 subjects who had undergone GBP surgery 1.5 +/- 0.7 years before testing and compared these responses with 6 obese subjects about to undergo GBP surgery, 6 obese nonsurgical subjects (matched for BMI to the post-GBP surgical group), and 5 lean subjects.
Results: Despite weight loss induced by the GBP surgery, fasting serum ghrelin levels were significantly lower in the post-GBP surgery group than in the lean subject (by 57%) or pre-GBP surgery (by 45%) group. Serum ghrelin levels during the OGTT were significantly lower in postoperative than in lean, obese pre-GBP surgical, or obese nonsurgical subjects. The magnitude of the decline in serum ghrelin levels between 0 and 120 minutes post-OGTT was significantly smaller in postoperative (by 62%), obese pre-GBP surgical (by 80%), or obese nonsurgical (by 69%) subjects in comparison with lean subjects.
Discussion: Serum ghrelin levels in response to OGTT are lower in subjects post-GBP surgery than in either lean or obese subjects. Tonically low serum ghrelin levels may be involved in the mechanisms inducing sustained weight loss after GBP surgery.