Whole Grains: A matter of processing

When a carbohydrate-rich food or meal is consumed, there is a subsequent rise in blood glucose, referred to as the postprandial blood glucose response. Studies suggest that whole-grain foods have a more favorable glycemic response compared to processed grains. Yet, the “whole grain” story is more complicated than previously thought. Study results published in The Journal of Nutrition now make it abundantly clear that, when assessing postprandial blood glucose responses to different whole grains, the effects of processing must be considered. 

The objective of this study conducted by Kathy Musa-Veloso (Intertek Health Sciences Inc.) and colleagues was to determine the effects of differently processed oats on the postprandial blood glucose and insulin responses relative to refined grains. Eleven electronic databases were systematically searched to identify studies published through May 2019. Randomized controlled trials comparing the postprandial blood glucose and insulin responses to oats compared with any refined grain were included if the carbohydrate content of the test meals was similar.  Ten publications were included, with oat kernels studied in 3 comparisons, thick oat flakes in 7 comparisons, and thin/quick/instant oat flakes in 6 comparisons.

Based on the results of the meta-analysis, when compared with the refined grain controls, only oats that were consumed as intact kernels or as thick oats resulted in reduced blood glucose and insulin responses. The effects on postprandial blood glucose and insulin responses were not significant between the consumption of thin oats and refined grain controls.

This is the first systematic review and meta-analysis in which the postprandial glycemic and insulin responses have been investigated separately for oat flakes of different thicknesses relative to refined grains.  When compared to a refined grain control food and the same amount of available carbohydrate, the postprandial glycemic and insulin responses elicited by intact oat kernels and thick oats were significantly lower. 

In conclusion, disruption of the structural integrity of oat kernels is likely associated with a loss in the glycemic benefits of oats. Nonetheless, the consumption of whole grain oats should be encouraged because whole grains are nutritionally superior to refined grains. However, to improve postprandial glycemic responses, this study shows that it is important to consider the type of whole grain and the impact of processing.

PepsiCo, Inc., which manufactures oatmeal products under the brand name Quaker Oats®, funded this systematic review and meta-analysis.  Intertek Health Sciences Inc. has provided consulting services to PepsiCo, Inc.  The views expressed in the publication are those of the authors and do not necessarily reflect the opinion or policies of PepsiCo, Inc or Intertek Health Sciences Inc.

References

Musa-Veloso K, Noori D, Venditti C, Poon T, Johnson J, Harkness LS, O’Shea M, Chu Y. A Systematic Review and Meta-Analysis of Randomized Controlled Trials on the Effects of Oats and Oat Processing on Postprandial Blood Glucose and Insulin Responses. The Journal of Nutrition, Volume 151, Issue 2, February 2021, Pages 341–351, https://doi.org/10.1093/jn/nxaa349.

Images via canva.com.