OC writes in the comments:
I was just reading your post on hormesis and plant toxins. Why would wheat (1 slice of bread once or twice per week) or an ocassional teaspoon of peanut butter not also cause hormesis. Is it absolutely determined that these substances are unhealthy, or is this also theoretical? I ask because my mom eats pretty healthy, but it's still difficult for her to give up her toast in the morning.
It's a non sequitur to assume that every stress or toxin must have or even might have a hormetic effect.
There is not likely any hormesis to be found with cerebral concussions, skin lacerations or lead oxide ingestion.
These won't kill you in limited amounts but they have no mechanisms where the body's response leaves you physiologically "better off" than before.
I am not saying that there is anything necessarily that harmful in a non-celiac eating a little bread, or anyone smoking a cigarette now and then, or not getting enough sleep once in a while, or anything else not wise done only once in a while. I am saying that if there is any damage associated with these behaviors, you can't automatically propose they are hormetic. You need evidence based on an actual mechanism to say they might be.
If your mom is at optimal weight and has no celiac disease or auto-immune fellow travelers of celiac, and one slice does not beget another (the main issue with all flour containing "foods") then, a slice of bread a day may be no big deal.
It's not the ten commandments, here folks, it's a framework. As long as you are honoring more in the observance than in the breach, you are on the right track.