Endocrine consequences of different types of bariatric surgery are not fully understood and may contribute to improvements in insulin sensitivity. The aim of this study was to assess changes in insulin sensitivity and plasma glucose, insulin and gut peptides one year after gastric bypass (RYGB; n=5), sleeve gastrectomy (SG; n=9) and gastric band (GB; n=7) surgery, compared with a low-calorie diet (LCD; n=9) control group. Thirty obese subjects (27 females; mean age=46±2y (22-62y); BMI=47.2±1.5kg/m2) underwent a 2-step hyperinsulinemic-euglycemic clamp (20 & 80mU·m-2·min-1 insulin) and a mixed-meal challenge (400kcal) at baseline, 8 and 52 weeks. Subjective ratings of appetite were obtained at fasting whereas insulin, glucose and gut peptides (GLP1, total and acylated ghrelin, PYY) were measured before and for 180min after the meal. Mixed models were performed to examine effects of group, time and group* time on outcomes of interest. After one year, RYGB and SG had achieved similar weight loss (SG=-34.9±2.8; RYGB=-37.5±3.5%), with 17.6±1.8% in GB and -1.0±1.7% in LCD participants. Insulin sensitivity (at both low and high insulin infusions), fasting and AUC glucose and insulin, and subjective ratings of satiety and desire to eat all improved with time (all P<0.05), but were not different between groups. However, there were significant group, time and group*time interactions (all P<0.05) for total and acylated ghrelin and PYY (fasting & AUC); none were observed for GLP1. In the whole cohort, greater improvements in whole-body insulin sensitivity were associated with larger increases in acylated ghrelin (fasting: r=0.4, P=0.05; AUC: r=0.47, P=0.02) at 8 weeks. At 52 weeks, greater improvements in whole-body insulin sensitivity were associated with smaller changes in total ghrelin AUC (r=-0.46, P=0.04). Our results indicate that ghrelin dynamics are a contributing factor to improved insulin sensitivity after weight loss.