Is Yeast evil?

I am starting to sell my sourdough loaves, which up till now have been 100% hard red or hard white ground in my Mockmill 200. They produce a nice loaf, nice enough for my family. I’m worried others I’m selling to won’t appreciate such a “dense” loaf, so I’ve considered using recipes that use both starter and instant yeast. However, my sister in law who is from Ukraine, has been unable to tolerate any kind of commercial yeast since coming to America one year ago. My sourdough loaves do not bother her.

So my question is this: is it yeast, or is it HOW yeast is processed in the bread? For example, if combined with sourdough, does that make it easier on your stomach? I’m also wondering if my sisters assumption of yeast being the problem is wrong - maybe it’s the preservatives or other ingredients?

I’ll take ANY thoughts or insights, or personal experiences. Thank you!!!

Yeast is dead once the loaf has been baked. So its not the yeast. Rather its what the yeast hasn’t done to the bread but the sourdough starter has and that is to make the bread more digestible.

That was my initial thought, “doesn’t it die?” Thank you very much, Abe!