Two oat species studies, starting with Avena nuda:

“Oats are a good source of carbohydrates and fibers. They contain more proteins and fats than other grains, and they are packed with vitamins (vitamin E, thiamine, etc.), minerals (Ca, Fe, Mn, etc.), and antioxidants (avenanthramides, ferulic acid, caffeic acid, flavonoids, etc.).

β-glucan contained in naked oats has multiple health benefits, including improving insulin sensitivity, lowering blood sugar levels, reducing risk of type II diabetes, and reducing low-density lipoprotein and total cholesterol levels.

There are two key enzymes in the hydrolysis of starch: α-amylase and α-glucosidase. Inhibiting activity of these enzymes can delay degradation of starch and absorption of glucose, thereby inhibiting rapid rise of postprandial blood glucose levels. α-amylase and α-glucosidase inhibitors are often used in treatment of type II diabetes.

This study investigated inhibitory effects of free and bound bioactive extracts from naked oats on amylase and glucosidase activity.

α-amylase inhibition by free (A) and bound (B) compound extracts from naked oats. The half maximal inhibitory concentrations (IC₅₀) of free and bound compound extracts were 0.09 and 1.33 mg/mL, respectively, higher than that of acarbose (0.03 mg/mL), the positive control.

Low digestibility of naked oats will help facilitate development of low-glycemic foods.”

https://www.sciencedirect.com/science/article/pii/S0023643821010550 “Endogenous bioactive compounds of naked oats (Avena nuda L.) inhibit α-amylase and α-glucosidase activity”

“Low digestibility of naked oats” referred to human capabilities, not to those of our gut microbiota. See A healthspan improvement for more on acarbose.

A second study investigated uses for Avena sativa hull and bran by-products:

“β-Glucan is mainly found in oat bran (OB) along with various phenolic compounds. Oat husk (OH) is a by-product produced during oat processing for food purposes, about 25–33% of its weight.

Ultrafine grinding or micronization is a new technique used for making a super fine powder with a particle size of 1–100 μm and good surface properties. This very fine powder is characterized by higher solubility, dispersibility, and water absorption, which improves quality of target food products. Micronization considerably enhances efficiency of extraction of phytochemicals, and is widely employed to extract natural polysaccharides from different bioresources.

OH is especially rich in insoluble fiber such as cellulose, hemicelluloses, and lignin, whereas both soluble and insoluble fiber occurs in OB in a ratio of 1:5. OB has a higher soluble dietary fiber content than wheat or rice bran.

The optimal composition, 60–70% of OH and 30–40% of OB, allows for obtaining a product with 60–70% fiber and enhanced antioxidant activity due to bioactive substances and their synergistic effect. The resulting product can be a valuable additive to various food and dietary supplements.”

https://www.mdpi.com/1420-3049/27/9/2621/htm “Fiber Preparation from Micronized Oat By-Products: Antioxidant Properties and Interactions between Bioactive Compounds”

See Oat species comparisons of the good stuff for more comparisons of their hulls.