Effects of very low calorie diets on liver size and weight loss in the preoperative period of bariatric surgery: a systematic review

Restrictive diet implementation in bariatric surgery (BS) preoperative period is common, although its benefits are not well established. This study aimed to assess the effects of very low calorie diets (VLCD) on liver size and weight loss during BS preoperative period. Surgery-related complications were also assessed. A systematic review of the literature was performed. Terms such as "bariatric surgery" and "very low energy diet" were included in the search strategy. Inclusion criteria were adult patients (aged>18 yr); VLCD treatment in BS preoperative period (10 d to 12 wk); and assessment of 1 the following outcomes: weight loss, liver volume reduction, and surgical complications. There were 9 studies included (849 patients including 250 controls, 196 controls without VLCD). Of the studies, 3 were randomized clinical trials and 6 were observational studies. VLCD treatment led to weight loss (-2.8 to -14.8 kg) and to liver size reduction by 5% to 20% of the initial volume. VLCD treatment did not significantly reduce perioperative complications. However, 1 study (n = 273) reported a protective effect 30 days after surgery. This systematic review found VLCD treatment led to significant weight loss and liver volume reduction when applied to patients with obesity in BS preoperative period. The effect of VLCD on surgical risks is not clear. Standardization of dietary characteristics is needed, because weight loss and decrease in liver size were not connected to higher caloric restriction. This is an important matter in clinical practice as to avoid unnecessary prolonged and/or excessive dietary restriction.