Dietary Patterns for Weight and Glycemic Management in Persons With Type 1 Diabetes: A Meta-analysis of Clinical Trials

Abstract

Background: Medical nutrition therapy is fundamental for managing glycemia and weight in type 1 diabetes, yet dietary guidance specific to this population and relevant subgroups is lacking.

Purpose: We synthesized the interventional literature investigating diet patterns for glycemic and weight management in youth and adults with type 1 diabetes, with attention to interindividual variation that suggests the need for precision approaches. The protocol was prospectively registered (CRD42024519941).

Data sources: AMED, CINAHL, Cochrane Library, Ovid MEDLINE, Ovid Embase, Google Scholar, and Web of Science Core Collection were searched from January 2011 to June 2024.

Study selection: Clinical trials ≥4 weeks with ≥10 youth and/or adults diagnosed with type 1 diabetes ≥6 months prior and reporting glycated hemoglobin (HbA1c) or weight were included.

Data synthesis: Twelve studies with 668 participants were included. Data were pooled by random-effects models for HbA1c and weight. Studies with insufficient data and subgroup differences were narratively synthesized per Synthesis without meta-analysis guidelines. Pooled results of very low to moderate certainty evidence showed no advantage of any particular diet pattern in randomized trials. Very low-quality evidence from single-arm low carbohydrate trials suggested improved HbA1c over time (-0.63% [95% CI, -0.99 to -0.27]; -6.0 mmol/mol [-10.8 to -3.0]). Wide pooled CIs suggested between-person heterogeneity; however, stratification of results by participant characteristics was rarely performed.

Limitations: Limited evidence precluded subgroup analyses to inform precision nutrition approaches.

Conclusion: Randomized trials are needed to confirm the efficacy of specific diets and determine whether precision nutrition therapies optimize glycemia and weight in persons with type 1 diabetes.

Keywords: diet patterns; hemoglobin A1c; meta-analysis; systematic review; type 1 diabetes; weight.

Figure 1.

Schematic of identified studies and summary of the certainty of evidence by diet pattern, study design, and study outcome. Figure was created using bioRender.

Figure 2.

Forest plots showing pooled estimates and 95% CIs from random effects regression models for randomized (A) and single-arm clinical trials (B) reporting HbA1c. The suffixes “_A” and “_B” were used to report separate effect estimates when more than 1 control arm was included. τ² (ie, Tau), I², H², and θ_i = θ_j (ie, the Cochrane Q test based on a chi-square distribution) are tests of heterogeneity; statistical significance (P < .05) would indicate that effects varied across studies, whereas P ≥ .05 indicates failure to reject the null that there is a lack of heterogeneity across studies. The test of θ indicates whether the pooled result for each diet pattern and study type is different from the null. Numbers in parentheses indicate the degrees of freedom representing n-1 studies. The test of group differences (Q_b) indicates whether the pooled results for randomized trials vary by diet pattern. Values for Nansel et al estimated from visual presentation of results. HbA1c values for individual studies included in meta-analyses are reported in mmol/mol in Tables S9 and 10 (16). Values were converted from % to mmol/mol using ngsp.org/convert1.asp.

Figure 3.

Forest plots showing pooled point estimates and 95% CIs from random effects regression models for randomized (A) and single-arm clinical trials (B) reporting weight (kg). The suffixes “_A” and “_B” were used to report separate effect estimates when more than 1 control arm was included. τ² (ie, Tau), I², H², and θ_i = θ_j (ie, the Cochrane Q test based on a chi-square distribution) are tests of heterogeneity; statistical significance (P < .05) would indicate that effects varied across studies, whereas P ≥ .05 indicates failure to reject the null that there is a lack of heterogeneity across studies. The test of θ indicates whether the pooled result for each diet pattern and study type is different from the null. Numbers in parentheses indicate the degrees of freedom representing n-1 studies.