Jeremy D. Krebs

Aim Very low carbohydrate/ketogenic diets (VLC/KDs) are popular but their role in managing pre‐diabetes and type 2 diabetes (T2D) is uncertain. This study uses a systematic review and meta‐analysis of randomized controlled trials to estimate the effect of these diets in this population. Materials and Methods A systematic review identified randomized controlled trials of at least 6 months duration comparing efficacy and safety of VLC/KDs (≤50 g carbohydrate or ≤10% total energy from carbohydrate per day) with a control diet (carbohydrate above the VLC/KD threshold) in adults with pre‐diabetes or T2D. The primary outcome variable was glycated haemoglobin (HbA1c) after 12 months. The meta‐analysis method was inverse variance weighting of mean values for continuous variables. Results Key word searches identified 2290 studies; 2221 were not in scope. A full text review of 69 studies identified eight meeting inclusion criteria; in total, it involved 606 participants. Six studies reported HbA1c (%) at 12 months; four as change from baseline with a fixed effects estimate (95% confidence interval): VLC/KD minus control of 0.01% (−0.22 to 0.25), p = .91; and two as change from baseline: −0.65% (−0.99; −0.31) [−7.1 mmol/mol (−10.8; −3.4)], p < .001. Serum triglycerides were lower with VLC/KD versus control: −0.28 mmol/L (−0.44 to −0.11), p < .001. High‐density lipoprotein was higher with an estimate of 0.04 mmol/L (0.01 to 0.08), p = .03, in the five studies reporting 12‐month summary data. Conclusions A VLC/KD may cause reductions in HbA1c and triglycerides in those with pre‐diabetes or T2D but evidence of an advantage over other strategies is limited. More well‐designed studies are required to provide certain evidence.