The present meta-analysis of randomised controlled trials (RCT) aimed to investigate the effect of oat intake on glycaemic control and insulin sensitivity. A literature search was carried out in PubMed, ScienceDirect Online and The Cochrane Library (up to October 2013) for RCT that assessed the effect of oat intake on glucose control and insulin sensitivity. A total of fifteen articles with 673 subjects met the inclusion criteria. A random-effects model was used when the overall pooled studies exhibited significant heterogeneity. Otherwise, a fixed-effects model was used. Compared with controls, oat intake significantly reduced the concentrations of fasting insulin by - 6·29 (95 % CI - 12·32, - 0·27) pmol/l (P= 0·04) and the values of glucose AUC (GAUC; 0-120 min) by - 30·23 (95 % CI - 43·65, - 16·81) min × mmol/l (P< 0·0001). There was a slight decrease in fasting glucose concentrations, glycated Hb concentrations and homeostatic model assessment-insulin resistance values in subjects who consumed oats, but the difference was not significant. In conclusion, oat intake significantly lowers fasting insulin concentrations and GAUC values. To further investigate the effect of oat intake on fasting glucose concentrations, additional long-term and high-quality RCT with a parallel design are required.
Alex’s Notes: I LOVE OATS. No doubt, I eat oatmeal daily, rotating between rolled and steel-cut oats. I also enjoy oat bran on occasion, mixed in some Greek yogurt to help thicken it and add volume. Yes, oats are a grain. However, they are gluten-free (unless cross-contaminated during processing) and truly stand above all others for their health benefits and comforting taste (with cinnamon and stevia). The study at hand only adds support to the notion that oats are not a bad guy, as it conducted a meta-analysis of randomised controlled trials (RCT) to quantitatively assess whether oat intake has a beneficial effect on glycaemic control and insulin sensitivity.
Overall, 15 studies comprising 673 individuals were included in the meta-analysis. The study lengths varied from one to 16 weeks, and all but five were in individuals with metabolic diseases (diabetes, obesity, etc.). Those other five were in healthy persons.
There was no significant effect of oat intake on fasting glucose concentrations, HbA1c concentrations, or HOMA-IR values. This is not really surprising given that fasting blood glucose levels are tightly regulated by the body and only change under extreme circumstances, and HOMAR-IR is dependent on the individual’s health status more so than a food. Also, HbA1c is a measure of the average plasma glucose concentration over prolonged periods of time and the study durations were a maximum of 16 weeks in duration, so one wouldn’t expect it to change, at least not significantly.
However, significant reductions in fasting insulin and glucose area under the curve were present. Moreover, subgroup analysis revealed these benefits extended to both healthy and diseased individuals. These effects are likely due to the beta-glucan content, which is able to not only slow the digestion of carbohydrates and delay gastric emptying, but is also fermented by the gut microbiota to release short-chained fatty acids and other beneficial compounds. Additionally, oats possess potent antioxidants compounds, and the main component – dihydroavenanthramide D – has been shown to protect pancreatic beta-cell function from assault.
In terms of quantity, no dose-dependent relationships were noted, with benefits being found with as little as five grams of oats consumed daily, making it is difficult to confirm the optimal dose for a dietary guideline to improve diabetic health. Regardless, it seems prudent to enjoy some oatmeal with cinnamon and stevia at least several days per week.