Increasing particle size of oat flours decreases postprandial glycemia and increases appetite in healthy adults

Consumption of oats is associated with lowered risks of type 2 diabetes and obesity. However, many oat-based products (e.g., breakfast cereals) use finely milled flours but are associated with health claims based on oats of larger particle sizes. The objective of this study was to test the hypothesis that increasing oat flour particle size will result in lower postprandial glycemia and appetite. Using a randomized-controlled, crossover design, 20 participants (10 males, 10 females; age: 25.3 ± 1.0 years; body mass index: 23.2 ± 0.6 kg/m²) consumed a serving of porridge made using 40 g of coarse (675.7 ± 19.6 µm), whole (443.3 ± 36.2 µm), fine (96.0 ± 2.1 µm), or a commercial (375.9 ± 14.8 µm) oat flour unmatched in available carbohydrate, protein, and dietary fiber content. After a 12-hour overnight fast, blood glucose, insulin, and appetite were measured at 15 to 30-minute intervals over 120 minutes posttreatment consumption. Coarse and whole flours led to lower blood glucose between 30 and 60 minutes (P < .02). Blood glucose area under the curve (AUC) was lower after coarse than fine and commercial oat flours (P < 0.03), and after whole than fine oat flour (P < .002). Both coarse and whole oat flours resulted in lower insulin AUC than finer flours (P < .05). Appetite AUC was lower after the commercial than coarse flour (P < .007). Controlling milling to produce coarser oat flour to add to common foods may have health benefits. This study was registered at ClinicalTrials.gov (NCT05291351).