The effects of low carbohydrate diets including intermittent fasting on body weight, glycaemia, and quality of life measures in adults with type 1 diabetes and overweight/obesity: a systematic review

Aims: Overweight and obesity are increasingly common amongst people with type 1 diabetes mellitus (T1DM). Low carbohydrate diets (LCDs) including intermittent fasting diets (IFDs) are popular in the general population, but the efficacy and safety of these diets for weight loss remains unclear in people with T1DM and overweight/obesity. It is also unclear whether eucaloric versus hypocaloric LCDs have a differential effect on metabolic and quality of life (QoL) outcomes. Data synthesis: This systematic review synthesised data from randomised and non-randomised interventional studies assessing the efficacy and safety of LCDs including IFDs in adults with T1DM; we included studies involving at least some participants with overweight/obesity. Co-primary outcomes included change in body weight/body mass index (BMI), HbA1c, and QoL measures. Secondary/exploratory outcomes included change in body composition, continuous glucose monitoring metrics, total daily insulin requirements, lipid profile, blood pressure, as well as adherence to the prescribed dietary regimen. The search yielded 3694 results, with 13 eligible papers (8 main papers, 5 sub-analyses). Meta-analysis was not possible due to study heterogeneity. Amongst the studies involving hypocaloric LCDs (n = 3, 2 studies involved IFDs), the majority reported significant reductions in body weight, but no significant change in HbA1c. Amongst the studies involving eucaloric LCDs (n = 5, no IFDs), the majority reported significant reductions in body weight and HbA1c. QoL measures were only available for the studies involving eucaloric LCDs, with no major adverse effects noted. None of the studies reported major safety issues. Conclusions: The limited evidence available showed that the majority of studies involving eucaloric or hypocaloric LCDs reported beneficial effects on body weight. The majority of studies involving eucaloric (but not hypocaloric) LCDs reported a modest benefit on HbA1c and no adverse effects on QoL measures. To confirm and expand on the findings of this review, further high-quality, larger scale randomised controlled trials are required specifically in people with T1DM and overweight/obesity.