I was listening to podcast which mentioned the super size me experiment. In which the person said that at first morgan spurlock didn’t get on too with so much mcdonadls but once his gut / microbiome adjusted he “felt” better. The theory is as we fed our bodies certain food, the microbiome which thrives on that food “have the capacity to manipulate behaviour and mood through altering the neural signals”. Source: https://www.ucsf.edu/news/2014/08/116526/do-gut-bacteria-rule-our-minds
So if you are consuming one type of diet, e.g. junk food and switch to a healthy whole food, your microbiome which is living off the junk food might react and trigger feeling bad or craving junk food as they fight to survive, but I don’t think you will be become intolerant, it’s just a passing phase while your guy adjusts.
There’s no definitive answer to this. For sure, if you do have a mild intolerance to something and then completely exclude it you are more sensitive so if you consume some of the food, it will give a harsher reaction.
However, I’ve only heard the theory that you can become sensitive to something if you exclude it. There’s no proof.