The effectiveness of a low carbohydrate, ketogenic diet prior to bariatric surgery A scoping review

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Abstract Background: Obesity prevalence has doubled since 1980, with 650 million adults obese in 2016, resulting in 4 million deaths. Bariatric surgery (BS) is considered the most effective and lasting therapeutic approach for the treatment of morbid obesity and its comorbidities in the long term. A low carbohydrate ketogenic diet (LCKD) is an emerging technique to help morbidly obese patients lose weight more rapidly. However, the overall success of this dietary approach in patients undergoing BS when compared to other diets is not yet fully determined. Aim: To scope the evidence base that examines the effect of LCKD on patients undergoing BS from different aspects such as weight loss, visceral fat, liver volume, biochemical markers, micronutrient status, and quality of life. Methodology: This scoping review uses Arksey and O′Malley's (2005) five stage scoping methodology. Various databases were searched: PubMed, EMBASE, MEDLINE, Science Direct, Web of Science, and Scopus as well as grey literature sites and Google searching. Results: Fifteen articles are included in this review: six published studies, seven conference abstracts and two blog articles. Most available literature shows the beneficial role of LCKD before surgery. LCKD leads to a reduction in weight of 10 to 16 kg after one month; reduction of visceral fat area ranged from 23 mm to 39 cm2;; reduced liver volume (p<0.05); improved lipid profile such as triglycerides, total cholesterol and LDL-cholesterol level (p<0.05); improved glucose profile, reported especially in T2DM patients which results in a decrease or stop of diabetic medications (p<0.05), and correction in the deficiency of micronutrients such as vitamin B12, folic acid, iron, and zinc. Further, LCKD may lead to some mild side effects due to adherence to the diet. Conclusion: Overall, a promising intervention was identified in this review. However, randomised clinical trials are required with a larger sample number to investigate the effectiveness of this diet before surgery. Moreover, further research is suggested to investigate the nutritional quality of KD, and the level of compliance and quality of life of preoperative LCKD.