Impact of whole cereals and processing on type 2 diabetes mellitus: a review

The prevalence of type 2 diabetes mellitus (T2DM) has been increasing throughout the world. The cereals, as the high carbohydrate food and dominant portion of diet, have crucial impacts on glycemic control, especially for T2DM. Both components in whole cereals and processing are closely related to their glycemic response. The consumption of whole cereals is shown to reduce the risk of T2DM. The starch characteristic of cereal determines its hydrolysis rate and glycemic response. The soluble and insoluble dietary fiber, phenolic compounds, and other bioactive constituents may slow down the starch hydrolysis. Besides, they have other physiological mechanisms in regulation of T2DM, such as amelioration of lipid disorder, antioxidant, anti-inflammation, and regulation of gut microbiota, which contribute to further improvement of metabolic symptoms. Cereals are subjected to processing before consumption, which is involved in mechanical force, bioprocessing, thermal treatment, and cooling. The processing induces changes in nutritional composition and physical structure compared to the raw kernels. The key influences of processing on glycemic response are the starch gelatinization and starch retrogradation. However, physical structure of cereal and interactions among starch and other compounds greatly contribute to various glycemic responses of cereal products. This review highlights recent findings on the influences of both bioactive constituents and processing on the antidiabetic effects and physiological properties of cereals.