Effects of Dietary Fiber and Low Glycemic Index Diet on Glucose Control in Subjects with Type 2 Diabetes Mellitus

OBJECTIVE: To review the effects of dietary fiber and a low glycemic index diet on glycemic risk factors in people with type 2 diabetes mellitus (T2DM) or T2DM and dyslipidemia. DATA SOURCES: Literature search was conducted using PubMed, Cochrane Library, The Natural Standard, and The Natural Medicines through July 2010 using the terms type 2 diabetes mellitus, dietary fiber, psyllium, and glycemic index. STUDY SELECTION AND DATA EXTRACTION: Articles included were randomized controlled studies or meta-analyses examining the effects of dietary interventions (dietary fiber, low glycemic index diet, or psyllium) on glycemic risk factors (glycosylated hemoglobin A(1c) [A1C] or postprandial plasma glucose [PPG] concentrations) in subjects with T2DM or T2DM and dyslipidemia. DATA SYNTHESIS: Both psyllium supplementation and low glycemic index diets have been studied as monotherapy in the treatment of T2DM. Seven studies were reviewed (3 randomized crossover studies, 1 randomized parallel study, 3 randomized blinded parallel studies). Individually, psyllium supplementation and a low glycemic index diet improved glycemic risk factors. PPG and A1C decreased with psyllium 10.2 g per day, while A1C decreased with a low glycemic index diet (average glycemic index 59). However, the results for the low glycemic index diet are controversial. One study was underpowered to detect changes in A1C, while another study had psyllium fiber as a confounding variable. CONCLUSIONS: Psyllium supplementation might be an additional therapeutic option for people with T2DM who are already receiving diabetes medication and who still experience elevated PPG concentrations. Further well-designed clinical trials and adjustment for confounding variables are needed to determine the role of a low glycemic index diet in the treatment of T2DM.