Is. Awful. Don't do it.
I went out for lunch at a Thai restaurant on a particularly stressful work day. I loaded two plates full of forbidden foods...rice noodles, spring rolls, pad thai, not to mention the soy, vegetable oil, etc. etc. And I have to say, its not that I really wanted them or was craving them (pre-GAPs this would have been the case). I was just at lunch at a place where nothing was allowed, so I cheated. (I can't really even call it indulging, because compared to GAPS fare this food was sadly lacking.)
I was unconvinced of the veracity of the claim that these foods produce opioid-like substances during digestion, which, for a person with a leaky gut, absorb into the blood and cause symptoms like fatigue, fuzzy thinking etc., in addition to triggering autoimmunity. I assumed these substances were marginally opioid-like and that the effect was minimal if detectable. Now that I'm able to compare the way I feel in relatively good health to the way I felt on these foods, I'm convinced. I mean seriously, even though this was just a lunch, the next day I felt like I'd killed a bottle of wine the night before.
So this is the first downside to GAPS. It becomes far more difficult to enjoy "ethnic" food from that is heavily based on carbs - Italian, Thai, Indian, etc. This said, factoring the cost of my lunch, the damage I did with it, and how I felt the next day , I can say now with total confidence that the cheat meal was not worth it.