Clinical evidence of low-calorie and ketogenic nutrological therapy before, during and after bariatric surgery: a systematic review

Introduction: Obesity is a multifactorial disease that causes serious comorbidities. There are more than 2.2 billion overweight and obese people in the world. Obese patients tend to be predisposed to micronutrient deficiency even before bariatric surgery, therefore, it is imperative to supplement nutrients orally, enterally, or parenterally, according to the indications of each patient. Objective: It was highlighted the importance of low-calorie and ketogenic nutritional therapy before, during, and after bariatric surgery through the systematic analysis of clinical studies. Methods: The systematic review rules of the PRISMA Platform were followed. The search was conducted from June to July 2024 in the Scopus, PubMed, Science Direct, Scielo, and Google Scholar databases. The quality of the studies was based on the GRADE instrument and the risk of bias was analyzed according to the Cochrane instrument. Results and Conclusion: 119 articles were found. A total of 40 articles were fully evaluated and 34 were included and developed in the present systematic review study. Considering the Cochrane tool for risk of bias, the overall assessment resulted in 23 studies with a high risk of bias and 27 that did not meet GRADE and AMSTAR-2. Most studies presented homogeneity in their results, with X2=76.5%>50%. It was concluded that nutrological therapy strategies could represent a possible alternative to other methodologies, especially when it is recommended to improve patient adherence to following the prescribed diet before bariatric surgery. Weight loss induced by the ketogenic diet before bariatric surgery has beneficial effects on reducing liver volume, metabolic profile, and intra- and postoperative complications. Knowledge of the type of bariatric surgery performed and an understanding of its anatomy and physiology are useful to provide optimal care to patients, especially in nutritional complications. Nutritional deficiencies and metabolic disorders result from “malabsorption” procedures such as RYGB. Immediate administration of thiamine is essential. Dextrose should be avoided in intravenous hydration until thiamine is adequately replaced. For all bariatric patients, a protein intake of 60-70 g/d and a multivitamin with iron and vitamin B12 supplementation is recommended. Daily calcium and vitamin D supplementation is also encouraged. In addition, serum micronutrient levels should be monitored regularly and additional supplementation should be prescribed as ind