A reader questioned one part of Oat species comparisons of the good stuff regarding Avena nuda hull digestibility. This 2019 study partially investigated that aspect:

“We investigated effects of proteins, lipids, and β-glucan in naked oat flour on in vitro digestibility of starch. Content of rapidly digested starch increased, and content of resistant starch decreased after removing non-starch constituents.

There are three categories of starch in accordance with the rate and degree of starch digestion, namely, rapidly digested starch, slowly digested starch, and resistant starch. Resistant starch cannot be digested. Instead, it promotes growth of beneficial colonic flora.

Digestibility of starch is influenced by size and shape of starch granules, food processing method, physical and chemical modifications, viscosity, and food matrix components. Physicochemical properties of naked oat starch and naked oat flour after removing non-starch constituents were compared to study relationships between starch digestibility and intrinsic factors:

Oats contain more proteins and lipids than other common grains. Proteins can effectively reduce starch digestibility by several mechanisms:

• Proteins can form a protection around starch granules, restricting entry of enzymes into substrates.
• Surface proteins can block catalytic binding of enzymes on starch granule exterior.
• α-amylase can partially bind to proteins, reducing enzyme utilization.

By contrast, effects of lipids on starch digestibility is primarily due to forming complexes with amylose, which is better able to resist amylase.

β-glucan, particularly the extracted water-soluble fraction, can lower digestion rate of starch by increasing viscosity. β-glucan can create a complex of adjacent proteins to form a robust structure that resists amylase, resulting in a decrease in starch digestibility.”

https://www.sciencedirect.com/science/article/abs/pii/S0308814619310556 “Non-starch constituents influence the in vitro digestibility of naked oat (Avena nuda L.) starch” (not freely available)

When viewing the above graphic, keep in mind that its order wasn’t sequential. So “degreased” oat flour (lipids removed, DG-NOF) wasn’t included in “deproteinized” oat flour (DP-NOF).

This in vitro study missed an opportunity to investigate human-practical aspects. Nobody eats oats without preparing them with water. But effects on digestibility from minutes and hours of soaking, boiling, microwaving, etc. weren’t analyzed.

Gut microbiota outnumber human cells. Treat them well with both Avena nuda resistant oat starch and indigestible hulls, and expect reciprocity.