My experience proved similar except it wasn’t a full fast. My diet evolved. First I removed oatmeal, peanut butter, then some food like night shades. Then I further removed most carbs. Now I seldom have allergies in the mornings. If I have a weekend of poor eating, I will have a few sneezing fits come Monday but nothing as severe as it used to be. I eat close to carnivore but add some veggies here and there.
Get rid of all processed foods. Then as you feel comfortable diminish nuts and grains, then some veggies. Dr Gundry spells the dangers with eating some legumes, grains, and even some veggies if not prepared right.
I did 4 elimination diets over several years. Couldn’t seem to find the culprit.
Got a blood allergy panel done a few months ago. A dozen things showed up, including milk, eggs, wheat, tomato, chocolate and … coffee. I would have never known on coffee without that test.
When i got everything out, my eyes spotted watering all day long and my exercise induced asthma disappeared. Still have eczema, so not sure why there.