Short-term effects of obesity surgery versus low-energy diet on body composition and tissue-specific glucose uptake : a randomised clinical study using whole-body integrated 18F-FDG-PET/MRI

Aims/hypothesis Obesity surgery (OS) and diet-induced weight loss rapidly improve insulin resistance. We aim to investi-gate the impact of either Roux-en-Y gastric bypass (RYGB) or sleeve gastrectomy (SG) surgery compared with a diet lowin energy (low-calorie diet; LCD) on body composition, glucose control and insulin sensitivity, assessed both at the globaland tissue-specific level in individuals with obesity but not diabetes. Methods In this parallel group randomised controlled trial, patients on a waiting list for OS were randomised (no blinding,sealed envelopes) to either undergo surgery directly or undergo an LCD before surgery. At baseline and 4 weeks after surgery(n=15, 11 RYGB and 4 SG) or 4 weeks after the start of LCD (n=9), investigations were carried out, including an OGTTand hyperinsulinaemic–euglycaemic clamps during which concomitant simultaneous whole-body [ 18 F]fluorodeoxyglucose-positron emission tomography (PET)/MRI was performed. The primary outcome was HOMA-IR change. Results One month after bariatric surgery and initiation of LCD, both treatments induced similar reductions in body weight(mean ± SD: −7.7±1.4 kg and −7.4±2.2 kg, respectively), adipose tissue volume (7%) and liver fat content (2% units).HOMA-IR, a main endpoint, was significantly reduced following OS (−26.3% [95% CI −49.5, −3.0], p=0.009) and non-significantly following LCD (−20.9% [95% CI −58.2, 16.5). For both groups, there were similar reductions in triglyceridesand LDL-cholesterol. Fasting plasma glucose and insulin were also significantly reduced only following OS. There was anincrease in glucose AUC in response to an OGTT in the OS group (by 20%) but not in the LCD group. During hyperinsuli-naemia, only the OS group showed a significantly increased PET-derived glucose uptake rate in skeletal muscle but a reduceduptake in the heart and abdominal adipose tissue. Both liver and brain glucose uptake rates were unchanged after surgery orLCD. Whole-body glucose disposal and endog