This 2021 review highlighted effects of processing oat products:

“Starch contents in oats ranges from 51% to 65%. Resistant starch (RS) accounts for 29.31% of starch content in raw granular form of oat starch.

RS in raw oat starch is RS2 starch, where its slow digestion is mainly due to the compact nature of starch granules making starch less accessible to enzymes. Since amylose–lipid complex is resistant to enzymatic breakdown, high lipid content in oats (3–7%) may be another reason why oat has a relatively high level of RS starch. This type of RS is called RS5.

Although RS2 occurs naturally, most starch needs to be cooked for consumption. RS3 that is formed due to recrystallization of gelatinized starch is more commonly consumed by processing via gelatinization and retrogradation.

β-glucans are found in cell walls of endosperm and aleurone layers of oats, accounting for 1.73-5.70% of oat grains dry basis. Oat β-glucans are not digested in the upper gastric tract, but instead can be consumed by gut microbiota in the colon. This kind of prebiotic can be fermented by colonic microbiota, resulting in production of short chain fatty acids (SCFA) metabolites.

From field to table, oats are processed into various foods for consumption, and these foods exhibit high variability of GI values:

• β-glucan dose and molecular weight are crucial determinants affecting viscosity and gastric emptying rate; and
• Higher content of protein in oats is an important factor that deserves attention.”

https://www.mdpi.com/2304-8158/10/6/1304/htm “Oat-Based Foods: Chemical Constituents, Glycemic Index, and the Effect of Processing”

Didn’t care for this focus on one dimension of health, glycemic index. Why not focus on healthy individuals’ behaviors? See An oats β-glucan clinical trial for more human in vivo evidence regarding β-glucan molecular weight.

I eat oats three times a day, and it’s worked out alright.