Reference Number: 688
Year: 2022
Link: Link to original paper
Health: Diabetes
Nutrition: Whole grain
Summary
Abstract
Background: Observational studies have indicated beneficial effects of whole grain consumption on human health. However, no evidence based on randomized controlled trials has been established. Our objective was to perform a systematic review and meta-analysis of randomized controlled trials to assess the effects of whole grain consumption in glycaemic control of diabetic patients. Methods: A comprehensive search in four databases (Web of Science, Pubmed, Scopus and Cochrane library) was conducted to collect potential articles which measured the roles of whole grain consumption on glycaemic control up to October 2021. Results: A total of 16 eligible trials involving 1068 subjects were identified to evaluate the pooled effect. The overall results indicated that compared with the control group, whole grain intake presented a significantly reduced concentration in fast plasma glucose (WMD =?0.51 mmol/L, 95% CI:?0.73,?0.28; I2 = 88.6%, p < 0.001), a homeostasis model assessment of insulin resistance (WMD =?0.39 µU × mol/L2, 95% CI:?0.73, ?0.04; I2 = 58.4%, p = 0.014), and glycosylated haemoglobin (WMD =?0.56%, 95% CI:?0.88,?0.25, I2 = 88.5%, p < 0.001), while no significant difference was observed in fast plasma insulin level between groups (SMD =?0.05, 95% CI:?0.25, 0.14; I2 = 40.7%, p = 0.120). In terms of incremental area under the curve (iAUC), data suggested that whole grain effected a significant decrease in Glucose-iAUC (WMD =?233.09 min × mmol/L, 95% CI:?451.62,?14.57; I2 = 96.1%, p < 0.001) and Insulin-iAUC (SMD =?4.80, 95% CI:?8.36,?1.23; I2 = 89.9%, p = 0.002), although only in a small number of studies. Of note, there is evidence for modest unexplained heterogeneity in the present meta-analysis. Conclusion: Whole grain consumption confers a beneficial effect on glucose metabolism in patients with diabetes. Regrettably, since relevant studies were scarce, we failed to provide confident evidence of whole grain consumption on acute effects including Glucose-iAUC and Insulin-iAUC, which should be addressed in further trials.
Summary of Findings
Background and Objective
Type 2 diabetes mellitus (T2D) is a chronic metabolic disease characterized by elevated blood glucose and impaired insulin action. Whole grains are widely recommended for general health and glycemic control due to their high content of dietary fiber, micronutrients, and bioactive compounds. However, clinical evidence from randomized controlled trials (RCTs) has been inconsistent, and the extent to which whole-grain consumption improves glycemic outcomes in individuals with diabetes has not been fully established. This study aimed to systematically review and quantitatively synthesize RCT evidence on the effects of whole-grain diets on key glycemic parameters among adults with diabetes or prediabetes.
Methods
Comprehensive literature searches were conducted in PubMed, Scopus, Web of Science, and Cochrane Library up to October 2021 to find eligible RCTs. Inclusion criteria were: adult participants with diabetes or prediabetes, randomized comparison of whole-grain diet versus a control diet (typically refined grains), and reported outcomes including fasting plasma glucose, glycosylated hemoglobin (HbA1c), fasting insulin, and insulin resistance measures. In total, 16 RCTs with 1,068 participants were included.
Key Outcomes:
Fasting Plasma Glucose (FPG)
Meta-analysis showed that wholegrain consumption significantly reduced fasting plasma glucose compared with control diets.
Glycosylated Hemoglobin (HbA1c)
Wholegrain diets were associated with significant reductions in HbA1c, a marker of long-term glycemic control.
Insulin Resistance (HOMA-IR)
Whole-grain consumption significantly improved insulin resistance.
Fasting Plasma Insulin (FPI)
Whole grains did not significantly change fasting insulin levels. The standardized mean difference (SMD) was ?0.05 (not statistically significant), indicating that dietary effects on insulin per se might be modest.
Additional Outcomes
Several RCTs also measured postprandial glucose or insulin area under the curve (iAUC), but these outcomes were reported in fewer studies and showed mixed findings. The evidence thus suggests that confidence in acute response data remains limited. Future trials were suggested to aim to clarify effects on postprandial responses and compare specific grain types.
Significance for the Baker
This systematic review and meta-analysis of RCTs demonstrates that wholegrain diets improve key markers of glycemic control, including fasting glucose, HbA1c, and insulin resistance, in adults with diabetes or prediabetes. These results reinforce dietary recommendations promoting whole grains for better metabolic health in diabetic populations.
