Analysis challenges link between type 2 diabetes, refined grains

Refined grains have come under fire in recent years, charged with contributing to various health conditions, including type 2 diabetes. New analysis, however, refutes the charge, claiming refined grains are not responsible for the development of type 2 diabetes (Mayo Clin Proc. 2022. DOI: 10.1016/j.mayocp.2022.05.004). 

Refined grains have been processed to remove the bran and germ, rendering a product that has improved shelf stability and other attributes, such as improved texture. However, this process can also impact the healthfulness of grains by stripping the products of dietary fiber, iron and certain vitamins. Commonly consumed refined grains include white flour and white rice.  

The 2020-2025 Dietary Guidelines for Americans (DGAs) recommends limiting refined grain intake to no more than half of total grain intake. According to the guidelines, most Americans are meeting the recommended intake of total grains, but the vast majority (98%) aren’t eating enough whole grains. Nearly three-fourths (74%) are eating too many refined grains.  

The push toward whole grains is attributed, per the guidelines, to scientific evidence showing reduced intake of refined grains was associated with lower risk of type 2 diabetes. 

However, new analysis, published in the Mayo Clinic Proceedings, counters the argument against refined grains. The commentary drew on data from all published observational cohort studies that looked at the associations between refined grain intake and risk of type 2 diabetes, comprising nearly 400,000 men and women. 

The analysis found refined staple grain foods, such as breads, cereal and pasta, were not associated with risk of type 2 diabetes. The study also explored the impact of indulgent refined grain foods, such as cakes, cookies and muffins, on type 2 diabetes risk, and found no association. Total grain intake was consistently associated with lower risk, the analysis showed. 

Importantly, several studies included in the analysis suggested that high consumption of white rice may increase risk of type 2 diabetes. This effect appeared to be mainly in Asian populations.   

The real culprit, according to the analysis, may be unhealthy Western diets high in red meat and sugar-sweetened beverages.   

“The results of these cohort studies are contrary to the conclusions of the 2015 and 2020 [Dietary Guidelines Advisory Committees (DGACs)],” the author wrote. “This is most likely because the DGACs relied primarily on studies of dietary patterns and their association with [type 2 diabetes] risk rather than on studies in which refined grain foods were considered as a distinct food category. The higher [type 2 diabetes] risk associated with the unhealthy (Western) dietary pattern is likely attributable to consumption of red and processed meat and sugar-sweetened beverages rather than to refined grain foods per se.” 

Rachel Adams joined Informa’s Health & Nutrition Network in 2013. Her career in the natural products industry started with a food and beverage focus before transitioning into her role as managing editor of Natural Products INSIDER, where she covered the dietary supplement industry. Adams left Informa Markets in 2019.