Effectiveness of Calorie Restriction for Weight Loss in Type 2 Diabetes Mellitus: A Systematic Review

The effectiveness of calorie restriction (CR) for weight loss in type 2 diabetes mellitus (T2DM) has not been thoroughly studied. This review aims to evaluate CR's short- and long-term effectiveness for weight loss and its impact on cardiometabolic parameters in T2DM. Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, Medline Complete, Embase, Cumulative Index to Nursing and Allied Health Literature (CINAHL), and Cochrane Library databases were searched to identify studies up to June 7, 2024. Furthermore, a reference search was conducted. Randomized controlled trials involving adults with T2DM examining CR and reporting weight changes were included. The revised Cochrane risk-of-bias tool was used to assess the study's quality. A narrative synthesis was used to analyze the findings. Eleven studies, with 1,554 participants, were included; all had a low risk of bias. The intervention group participants' mean baseline weight and Body Mass Index were 93.3 kg and 32.7 kg/m², respectively. Interventions used included total diet replacement (TDR) and very low- and low-calorie diets lasting 12 weeks to two years. CR with TDR resulted in >12% weight loss. Additionally, CR improved cardiometabolic parameters; glycated hemoglobin (HbA1c) decreased to ≤6.5%; diabetes remission was achieved in 19% to 83%; high-density lipoprotein significantly increased; and triglyceride, systolic, and diastolic blood pressure significantly decreased. In conclusion, CR effectively reduces weight and improves cardiometabolic markers in T2DM. However, large long-term studies addressing CR in T2DM are lacking, which challenges drawing firm conclusions. This highlights the need for further research to address this gap. This review is registered in the International Prospective Register of Systematic Reviews (PROSPERO) under the registration number CRD42024573505.