Clinical Impact of Enteral Protein Nutritional Therapy on Patients with Obesity Scheduled for Bariatric Surgery: A Focus on Safety, Efficacy, and Pathophysiological Changes

Background: Ketogenic diet-induced weight loss before bariatric surgery (BS) has beneficial effects on the reduction in the liver volume, metabolic profile, and intra- and post-operative complications. However, these beneficial effects can be limited by poor dietary adherence. A potential solution in patients showing a poor adherence in following the prescribed diet could be represented by enteral nutrition strategies. To date, no studies describe the protocol to use for the efficacy and the safety of pre-operative enteral ketogenic nutrition-based dietary protocols in terms of weight reduction, metabolic efficacy, and safety in patients with obesity scheduled for BS. Aims and scope: To assess the clinical impact, efficacy, and safety of ketogenic nutrition enteral protein (NEP) vs. nutritional enteral hypocaloric (NEI) protocols on patients with obesity candidate to BS. Patients and methods: 31 NEP were compared to 29 NEI patients through a 1:1 randomization. The body weight (BW), body mass index (BMI), waist circumference (WC), hip circumference (HC), and neck circumference (NC) were assessed at the baseline and at the 4-week follow-up. Furthermore, clinical parameters were assessed by blood tests, and patients were asked daily to report any side effects, using a self-administered questionnaire. Results: Compared to the baseline, the BW, BMI, WC, HC, and NC were significantly reduced in both groups studied (p < 0.001). However, we did not find any significative difference between the NEP and NEI groups in terms of weight loss (p = 0.559), BMI (p= 0.383), WC (p = 0.779), and HC (p = 0.559), while a statistically significant difference was found in terms of the NC (NEP, −7.1% vs. NEI, −4%, p = 0.011). Furthermore, we found a significant amelioration of the general clinical status in both groups. However, a statistically significant difference was found in terms of glycemia (NEP, −16% vs. NEI, −8.5%, p < 0.001), insulin (NEP, −49.6% vs. NEI, −17.8%, p < 0.0028), HOMA index (NEP, −57.7% vs. NEI, −24.9%, p < 0.001), total cholesterol (NEP, −24.3% vs. NEI, −2.8%, p < 0.001), low-density lipoprotein (NEP, −30.9% vs. NEI, 1.96%, p < 0.001), apolipoprotein A1 (NEP, −24.2% vs. NEI, −7%, p < 0.001), and apolipoprotein B (NEP, −23.1% vs. NEI, −2.3%, p < 0.001), whereas we did not find any significative difference between the NEP and NEI groups in terms of aortomesenteric fat thickness (p = 0.332), triglyceride levels (p = 0.534), degree of steatosis (p = 0.616), and left hepatic lobe volume (p = 0.264). Furthermore, the NEP and NEI treatments were well tolerated, and no major side effects were registered. Conclusions: Enteral feeding is an effective and safe treatment before BS, with NEP leading to better clinical results than NEI on the glycemic and lipid profiles. Further and larger randomized clinical trials are needed to confirm these preliminary data.