Plant Tissue Structure and Degree of Milling as Determinants of Starch Digestibility and Postprandial Metabolic Responses to Cereal and Legume Products

Background: Growing evidence suggests that the structural integrity of plant tissues is an important determinant of starch digestibility and postprandial metabolic responses in cereals, legumes, and starch-rich foods. This narrative review evaluates the influence of botanical tissue architecture and the degree of milling on physicochemical properties, product quality, starch digestibility, and metabolic responses in cereal- and legume-based foods. Methods: The evidence was critically synthesized from studies on physicochemical characterization, in vitro starch digestibility, acute postprandial and long-term human intervention studies, and relevant systematic reviews and meta-analyses. Results: The preservation of intact cells, cellular aggregates, and coarser flour fractions limits water penetration and delays starch swelling and gelatinization, whereas extensive milling increases starch damage and susceptibility to enzymatic hydrolysis. Botanical origin further influences these effects, with legumes generally exhibiting lower starch digestibility than cereals because of their thicker and less permeable cell walls. Increasing the proportion of coarse flour fractions may also impair loaf volume, texture, processing performance, and consumer acceptability. Acute postprandial human intervention studies typically report attenuated glycemic responses following consumption of structurally preserved cereal- and legume-based foods, with several studies also showing improved insulinemic and incretin responses. However, human evidence is more heterogeneous than the relatively consistent in vitro evidence for slower starch hydrolysis with greater preservation of cellular structure, and these effects do not necessarily translate into lower postprandial glycemic responses. Evidence regarding appetite regulation and long-term metabolic outcomes remains limited or inconsistent. Conclusions: Cellular integrity and botanical structure are important but under-recognized determinants of carbohydrate functionality. Preserving plant tissue structure by controlling the degree of milling may contribute to the modulation of starch digestibility and postprandial metabolic responses. Integrating structural characteristics alongside nutrient composition may support the development of healthier cereal- and legume-based foods while maintaining technological functionality, consumer acceptability, and metabolic health.