This is an old thread, but I want to be the person who disagrees that a sick person should stop OMAD when they are sick. It depends on what is wrong with you, probably; but one of the things that we can observe in nature is that most all of the animals do not eat when they get sick. Many health experts also recommend fasting when you are sick, at least at first.
This gives your body time to concentrate on fighting off the virus (or whatever infection) without having to also try to take care of the whole digestion process.
When we are fasting, and burning ketones for fuel, our body makes one ketone (BHB) that actually supports the immune system.
Anytime that I have had the flu, or been very sick for some reason, I was not hungry until I started to recover, and I only drank liquids for a few days until I started getting better. Once I was feeling better, then my appetite returned.
There is no real reason that we have to eat just because we are sick. Our body burns fat when we are fasting, and it can do that whether we are well or sick, and it simply takes care of a lot of work the body doesn’t have to deal with if we are not eating.
I am a total believer that we should listen to our body if it is telling us not to eat.
https://www.healthline.com/nutrition/can-fasting-fight-the-flu-or-cold#section2