Carbohydrate Quality Versus Quantity in Gestational Diabetes Mellitus While Considering Randomized Dietary Interventions: A Systematic Review

Medical nutrition therapy is the first-line treatment for gestational diabetes mellitus (GDM), but whether carbohydrate quality or quantity should be prioritized is unclear, as dietary interventions often change amount, glycemic quality, fiber, fat, protein, and food pattern together. We systematically reviewed randomized trials of carbohydrate quality or quantity in diagnosed GDM. PubMed and the Cochrane Central Register of Controlled Trials (CENTRAL) were searched from inception to July 19, 2026, with citation searching. Two human reviewers screened the records and extracted the data with artificial-intelligence assistance. Risk of bias was assessed using the revised Cochrane risk-of-bias tool (RoB 2), and the findings were primarily synthesized narratively using the Synthesis Without Meta-analysis (SWiM) approach, with limited random-effects meta-analysis for clinically compatible insulin-related outcomes. From 981 records, 34 reports representing 25 independent randomized studies were included; they differed markedly in construct, achieved carbohydrate separation, rescue treatment, and analysis population. In an exploratory, treatment-threshold analysis, lower-glycemic-index assignment reduced the proportion meeting insulin-start criteria (two trials, 159 participants; risk ratio [RR] 0.43, 95% confidence interval [CI] 0.25-0.75), but rescue switching removed the difference in actual insulin use. Lower-carbohydrate assignment did not reduce insulin initiation (three trials, 248 participants; RR 1.02, 95% CI 0.76-1.35). This finding remained essentially unchanged after excluding the trial in which the intended difference in carbohydrate intake was not achieved. With only two or three small trials per pool, I² = 0% does not indicate homogeneity. Fiber, staple-quality, and provided-diet interventions improved selected postprandial measures, but obstetric, birth-size, and neonatal-adiposity benefits were not established, and certainty was low or very low. Carbohydrate quality is a plausible route to postprandial improvement without aggressive restriction, but current randomized evidence does not establish a universal quality-over-quantity rule or support lower carbohydrate intake as superior. Carbohydrate amount should be individualized while prioritizing nutrient-dense, lower-glycemic-index, fiber-rich sources.