Aims/hypothesis <p>This systematic review and meta-analysis aimed to investigate the effects of time-restricted eating (TRE) on glucose metabolism and regulation in individuals with prediabetes (fasting blood glucose of 5.6–6.9 mmol/l or HbA_1c of 39–47 mmol/mol [5.7–6.4%]) or type 2 diabetes (fasting blood glucose ≥7 mmol/l or HbA_1c ≥48 mmol/mol [6.5%]).</p> Methods <p>A literature search was performed in MEDLINE, Embase and CENTRAL from inception to 5 August 2025. Moreover, forward and backward citation searches were performed. Eligible studies were RCTs in adults with prediabetes or type 2 diabetes, lasting ≥2 weeks, reporting markers of glucose metabolism and regulation, comparing TRE (≤12 h eating window) with a non–time-restricted control diet. Studies involving pregnancy, other fasting regimens, or non–peer-reviewed publications were excluded. Data were pooled as weighted mean differences with 95% CIs using random-effects generic inverse variance models in Cochrane Review Manager Web, and results are presented as forest plots. The certainty of evidence was defined using Grading of Recommendations, Assessment, Development and Evaluations methodology, and risk of bias was estimated by using the Revised Cochrane risk-of-bias tool for randomised trials (RoB 2).</p> Results <p>Out of 2043 records identified through the database search, as well as 1249 from forward and backward citation searches, ten RCTs including 599 participants were included. The mean length of the studies was 4 months, and the eating windows ranged from 4 to 10 h per day. The pooled meta-analysis showed no overall effect of TRE on HbA_1c (−3.33 mmol/mol; 95% CI −6.87, 0.20 (−0.30% points; −0.63, 0.02); <i>p</i>=0.06, moderate certainty). Nevertheless, following stratification by subgroups, TRE resulted in a reduction in HbA_1c of 0.93 mmol/mol (−1.70, −0.17 [−0.09% points; −0.16, −0.02]; <i>p</i>=0.02) in individuals with prediabetes but not in individuals with type 2 diabetes (−4.68 mmol/mol; −10.08, 0.72 (−0.43% points; −0.92, 0.07); <i>p</i>=0.09). TRE reduced fasting blood glucose in the pooled analysis (−0.30 mmol/l; −0.53, −0.07; <i>p</i>&lt;0.01, moderate certainty) as well as in the subgroup analyses in individuals with prediabetes (−0.14 mmol/l; −0.27, −0.01; <i>p</i>=0.03) and with type 2 diabetes (−0.48 mmol/l; −0.78, −0.17; <i>p</i>&lt;0.01). Moreover, TRE lowered body weight by 1.6 kg (−2.2, −1.0; <i>p</i>&lt;0.001) in the pooled analysis. The evidence was limited by imprecision arising from wide confidence intervals in some of the included studies, which may be due to small sample sizes. Lastly, the effects of TRE on markers of insulin sensitivity, beta cell function and continuous glucose monitoring measurements were inconclusive.</p> Conclusions/interpretation <p>Moderate-certainty evidence indicates that TRE reduces fasting blood glucose but not HbA_1c. The subgroup analyses revealed that TRE improved HbA_1c and fasting glucose in individuals with prediabetes and improved fasting glucose in individuals with type 2 diabetes. Future large-scale studies should investigate long-term effects of TRE in prevention and treatment of type 2 diabetes.</p> Trial registration <p>PROSPERO CRD42024523591</p> Funding <p>This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors. Three authors (JS, A-DT, THA) are employed at Steno Diabetes Center Copenhagen, a public hospital and research institution under the Capital Region of Denmark, partly funded by a grant from the Novo Nordisk Foundation.</p> Graphical Abstract <p></p>