In general you will “feel bad” when you eat foods that you are allergic to or that don’t agree with you. There are a wide variety of symptoms you could possibly get, so you really have to be “in-tune” with you body to notice any changes.
Examples include IBS, heart palpitations, headaches, mucous production (cough), the leaky gut “burn”, muscle twitching, etc, etc (I could list maybe 10 more if I spent time on it). There is also “die off” reactions which is candida dying from the foods you eat, but you shouldn’t get this from foods on the allowed foods list.
I use the coconut oil as a butter replacement!