Effect of a very low-carbohydrate ketogenic diet vs recommended diets in patients with type 2 diabetes: a meta-analysis

Abstract Context There is renewed interest in using very low-carbohydrate ketogenic (VLCK) diets to manage diabetes. Many clinical trials have been published, often with mixed results. Objective This meta-analysis compares the effect of a VLCK diet on glycemic control, body weight, lipid profile, medication use, and dropouts with that of recommended diets for 12 weeks or longer in people with type 2 diabetes. Data Sources Ovid MEDLINE, Ovid Embase, CENTRAL, and CINAHL databases were searched (January 1980 through September 2019). Study Selection Two authors independently reviewed search results to select randomized controlled trials (RCTs) comparing a VLCK diet (carbohydrate intake < 50 g/d or < 10% of total energy) with any recommended diet for type 2 diabetes in adults. Discrepancies were resolved after consulting with the third author. Data Extraction Eight RCTs with 648 participants were identified. Results Compared with control diets, the VLCK diet resulted in a greater decrease in hemoglobin A1c after 3 months (weighted mean difference[WMD]: −6.7 mmol/mol; 95%CI, −9.0 to −4.4) (WMD: −0.61%; 95%CI, −0.82 to −0.40; P < 0.001; moderate-certainty evidence) and after 6 months (WMD: −6.3 mmol/mol; 95%CI, −9.3 to −3.5) (WMD: −0.58%; 95%CI, −0.85 to −0.32; low-certainty evidence). There was a significantly greater weight loss with the VLCK diet after 3 months (WMD: −2.91 kg; 95%CI, −4.88 to −0.95; low-certainty evidence) and after 6 months (WMD: −2.84 kg; 95%CI, −5.29 to −0.39; low-certainty evidence). The VLCK diet was not better than a control diet after 12 months. It was superior in decreasing triglyceride levels, increasing high-density lipoprotein cholesterol levels, and reducing the use of antidiabetic medications for up to 12 months. Conclusion The VLCK diet appears to control glycemia and decrease body weight for up to 6 months in people with obesity and diabetes. Beneficial changes in serum triglycerides and high-density lipoprotein cholesterol, along with reductions in antidiabetic medications, continued in the VLCK group until 12 months. However, the quality of currently available evidence is not sufficient to recommend VLCK diets. A major limitation of the VLCK diet is patients’ lack of adherence to carbohydrate restriction. Systematic Review Registration PROSPERO registration number CRD42020154700