Intermittent fasting versus low-calorie diet for preoperative optimization before sleeve gastrectomy: a randomized controlled trial

Preoperative weight reduction is an essential component of bariatric care because it decreases liver volume, improves metabolic status, and facilitates surgical procedures. Although low-calorie diets (LCDs) are routinely recommended, the potential benefits of intermittent fasting as a preoperative strategy remain insufficiently investigated . Fifty-four patients (mean age 40.59 years; 59.25% female) were randomized into intermittent fasting diets (IFD) ( n = 27) or LCD ( n = 27) groups for 30 days. Anthropometrics, body composition, lipid profiles, liver enzymes, and liver size were assessed at baseline and post-intervention. Intraoperative duration, hospital stay, and Quality of Recovery scores at 24 and 48 h were also evaluated. Both interventions significantly improved anthropometric parameters (all P < 0.001). However, the IFD group achieved greater reductions in body weight ( P < 0.001), body mass index ( P = 0.002), waist circumference ( P < 0.001), fat mass ( P < 0.001), and body fat percentage ( P = 0.001), without additional loss of lean mass. Significant between-group differences favored IFD for total cholesterol, LDL-C, HDL-C (all P < 0.001), and AST ( P = 0.03). Hepatic steatosis grade significantly decreased from baseline to Day 30 in both the LCD ( P = 0.034) and IFD ( P < 0.001) groups, with a greater reduction in the IFD group ( P = 0.001). Liver size decreased significantly in both groups, with a greater reduction observed in the IFD group ( P = 0.009). Moreover, IFD was associated with shorter hospital stay ( P = 0.01) and higher QoR-40 scores at both 24 and 48 h after surgery. A 30-day preoperative 16:8 intermittent fasting regimen appears more effective than a conventional LCD for improving body composition, metabolic health, liver-related outcomes, and early postoperative recovery in patients undergoing sleeve gastrectomy, supporting its potential role as a practical strategy for preoperative optimization. Trial Registration The trial was registered in the Iranian Registry of Clinical Trials (IRCT). Registration number: IRCT20200301046655N2; registration date: [August 13, 2023].