A thought like this came into my mind when I was providing an answer to question related to this one here. The truth is, OMAD has the potential of causing ulcer. The practice can't stop to boggle my mind on how someone would be starving his/her all in the name of trying to be fit while there are other sure-proof ways this can be achieved.
On the tendency of OMAD cause of ulcer, research has it that long abstenance from food can lead to ulceric condition, because the microflora organisms responsible for the degradation of food substances become deprived of nutrients, as a result, they would turn on the intestinal walls of the digestive system. And this would definitely lead to ulcer if there's continuance avoidance of food when one is hungry.
As for me, I would kindly suggest that if anyone wants to practice OMAD, there shouldn't be hundred percent adherent to it, because the health risks could outweigh it benefits if not done prudently.