I've been eating once a day for the past 3.5 years and I'd read about the supposed immune system benefits. I've not had a cold/flu since then and I used to get 3-4 a year, so I'm sticking with it and I've become used to it anyway.
This is obviously just anecdotal, but for me, I certainly feel more mentally alert during a fasted state; though I wouldn't say I've been sick any more / less than other times in my life.
Friends think I'm quite bizarre for eating this way - but it just seems to work for me.
I've been doing something similar over the last few months - a very light breakfast, a solid lunch, and then no dinner - but for me, doing this was with the purpose of losing weight - which did happen, at the rate of just under 1 kg a week.
Also, you need to try it yourself. Every body is different.
You should try things like multiple small meals, or one big meal, or no carbs, or no gluten and honestly evaluate how they impact your life.
Whenever I try eating once a day or a fast, I feel fine, except that without fail I have diarrhea.