Effect of rye consumption on markers of glycemic control: evidence on the “rye factor”: a systematic review and meta-analysis of randomized controlled trials

Rye, as a source of dietary fiber, may have beneficial effects in glycemic control. In the current meta-analysis, we collected randomized controlled trials (RCTs) that examined the effect of rye consumption on glucose and insulin markers. PubMed, Scopus, and Web of Science databases were searched to find the RCTs. Random-effects model was used to calculate mean difference and 95% confidence intervals. Thirty-one RCTs, including 922 participants, passed the screening and eligibility stages and were included in the meta-analysis. Rye consumption did not have a significant effect on glucose indices including fasting, postprandial, and area under the curve (AUC). Subgroup analysis did not make a difference in the results, except that there was trends for increased postprandial glucose in two subgroups: individuals aged > 50 y (weighted mean difference (WMD) = 0.93, 95% CI: -0.03, 1.90 mmol/l, P = 0.058) and short intervention lengths (≤ 270 min) (WMD = 0.48, 95% CI: -0.03, 0.99 mmol/l, P = 0.066), and a trend for decreased AUC for glucose in rye fiber doses ≥ 12 g (WMD = -0.22, 95% CI: -0.46, 0.01 mmol/l, P = 0.059). Rye consumption did not show an effect on fasting and postprandial insulin but indicated a reduction in AUC for insulin (WMD = -0.48, 95% CI: -0.66, -0.30 mU/l, P < 0.001). Overall, results of this meta-analysis suggest that rye consumption may reduce insulin postprandial AUC without affecting glucose markers. Prospective cohorts are needed to determine the clinical importance of the finding.