Effectiveness of preoperative dietary interventions to induce weight loss prior to elective non-bariatric major abdominal surgery: a systematic literature review

Introduction: Obesity, excess visceral fat, and high liver volume due to hepatosteatosis (fatty liver) are risk factors for complications arising from major surgical procedures within the abdomen. In contrast to bariatric (weight loss) surgery, research on preoperative dietary interventions to induce weight loss for non-bariatric surgery patients with obesity is scarce, with a lack of consensus for the best approach. This review examined the outcomes of preoperative dietary approaches aimed at reducing weight prior to major non-bariatric abdominal surgery in adults with obesity.Materials and methods: PPRISMA guidelines were followed, and four electronic databases (MEDLINE, CINAHL, Embase, Cochrane Trials) were searched for interventional studies (with or without a control group) that evaluated efficacy of dietary interventions used preoperatively for the purpose of reducing excess weight/fat in preparation for major (invasive) elective surgical procedures within the abdomen in adults with obesity. Articles with bariatric surgery focus or interventions using pharmacotherapy/exercise only were excluded. Data extracted included: characteristics of the studies, participants and surgery, and outcomes of dietary adherence and anthropometric measures.Results: Ten studies, including five randomized controlled trials (RCTs), were eligible. In total, 764 participants (53 ± 11 years, 61% female, body mass index 33.5 ± 6.9) were awaiting liver resection/transplant (n = 3 studies), hernia repair (n = 3 studies), laparoscopic cholecystectomy (n = 2 studies), gastrectomy (n = 1 study), or a combination of these procedures (n = 1 study). Preoperative diet duration ranged from 1–68 weeks (median 5 weeks). Seven studies used a very low calorie diet (VLCD, ≤800 kcal/day, n = 6 meal replacement shakes, n = 1 food-based). Two studies used a low calorie diet (LCD, ≤900 kcal/day, n = 1 meal replacement shakes, n = 1 food-based), and one used general healthy eating. Surgical procedures that were in proximity to the liver (n = 6) used VLCD/LCDs of 1–3 weeks duration, primarily to reduce fatty liver. Mean weight loss across all studies was 7.5 ± 8 kg (range 1.4–24 kg), with waist circumference loss of 4.5 ± 1.7 cm. VLCDs (n = 7 studies, n = 347 participants) elicited a mean weight loss of 7.7 ± 9.3 kg over a median of 3 weeks (range 1–68 weeks).Conclusion: The review demonstrated significant weight loss is achievable using VLCDs/LCDs prior to major elective abdominal surgery for adults with obesity. Future RCTs should explore the impact of these interventions on postoperative outcomes