The Effect of Bread Consumption on Glycemic Control – A Systematic Review and Meta-Analysis of Intervention Studies

OBJECTIVES: Bread is a main carbohydrate sources in most diets and may hence be relevant for several health outcomes. This systematic review evaluated the effect of bread consumption on glycemic control in adults with and without type 2 diabetes mellitus (T2DM). METHODS: A systematic literature search was performed in September 2020 using Medline, Embase, Web of Science and the Cochrane Library. Eligible studies had to employ different types of bread in adults with or without T2DM and report glycemic outcomes (primary outcome: mean difference (MD) in fasting blood glucose between intervention and control groups; secondary outcomes: MD in fasting insulin, HOMA-IR, and glycated hemoglobin (HbA1c)). Data were pooled using generic inverse-variance with random effects model and presented as mean MD between treatments with 95% confidence intervals (95% CIs). RESULTS: Twenty-one studies met the inclusion criteria, providing data on 966 participants. Compared to control breads, the consumption of the intervention breads resulted in lower values of fasting blood glucose (MD −0.21 mmol/L, 95% CI −0.39 to −0.03, I(2) = 89%), yet no differences in fasting insulin (MD −1.60 pmol/L, 95% CI −6.10 to 2.91, I(2) = 42%), HOMA-IR (MD −0.08, 95% CI −0.39 to 0.23, I(2) = 63%) or HbA1c (MD −0.12%, 95% CI −0.40 to 0.17, I(2) = 60%). The included studies showed a great degree of heterogeneity. CONCLUSIONS: The type of bread influences fasting blood glucose in adults with and without T2DM. This argues for a mechanistic role of bread quality in metabolic health and calls for its consideration in future health policies. FUNDING SOURCES: The project has received funding from the German and Norwegian Research Council under the umbrella of European Joint programming Initiative “A healthy diet for a health life” (JPI-HDHL) and of the ERA-NET Cofund HDHL INTIMIC (GA N 727,565 of the EU Horizon 2020 Research and Innovation Programme).