When I still could do a very serious, wrong, high-carb day (the most I could do NOW - not now, I really don’t want any carbs in the near future but this year - is 12 servings of candies, nothing serious. the portions are tiny like 1 Timtam :D)…
I still ate a lot of fatty protein, of course and then lots of carbs. The wrong kind, not just a loaf of bread, I am WAY worse with sugar especially added one in some store-bought stuff.
Well.
After a few paleo-ish month, it was a pretty recognizable blow. I probably even got comfortable, maybe bloated (I don’t know what bloating is as I am not sure I ever had that but it seems the right word…?) with borderline stomach pain so pretty serious in my books. But I had to try 
After some carnivore-ish time, the same does nothing. I seem to have some weekly carb quota, I experienced it zillion time in my several on/off keto years. So as long as I come back soon, I am fine. BUT it’s still noticeable that it’s not my ideal way of eating. My energy, mind and healthiness feels about the same (unless in extreme circumstances. I couldn’t eat a ton of almost pure sugar alone but that probably would be not nice), it’s a subtle feeling. And of course, in my case carbs bring their stupid lack of satiation/satisfaction, I need to eat more and more… I still can choose my proper food at that point (at least now that I don’t really want to wrong things. I may be curious and try them but much of them seems pointless. only compulsions can do it but as time passes, they are less frequent) and that solves most of the problems.
So that’s me. One day can’t cause much bad as I just won’t abandon my precious eggs and meat, I still eat them. Maybe less but they still mitigate the problems, quite seriously.
If it’s my carbier day #11 (not high-carb, I always bounced back early and it just got better), well that’s bad news, even a little off eating upsets my body (nausea, belly ache, bloating. not fun). I have a smart but pretty indulgent body but if it reaches its limits, it puts its foot down and it’s the right thing to do. I shouldn’t be an idiot, seriously.
I’ve read other people’s stories, a lot of them.
The experiences are all over the place. Some people can do more than me: they just start to eat high-carb, continue for years and they just don’t feel the irresistible pull back that I feel almost immediately. No pain or anything either.
But some people just eat a tiny bit of wrong carbs (it’s vegetables for some people, amazing how different we are) and they are in pain for hours at least.
Most of us are in-between. And it’s not always the same. It depends, obviously. I mentioned what are important factors for me. How many carbs I ate recently? Less is better. Amounts matter a lot, obviously. Type of carbs. What I ate before and especially after the carbs. Or with. I can do some sugar poisoning on keto just fine if I go and grab a bunch (I mean, not 5g or something. still not much, obviously) of very sugary fruit and eat it all alone. Sausage afterwards? Nothing happens. I still am aware that it is some lovely candy, not proper food for my body.
Rare, subtle off eating is a way better idea for me but we are all different. And sometimes I choose one very carby day over 14 lowish-carb ones especially that certain carbs mess with my mind, though that’s a good sign that I just should forget about it or train myself more.
(A carby day always helps with my fasting, though… I just get super satiated for quite long - still no EF happens, usually so not that long - , no wonder as I eat bigger meals… Once I wanted OMAD for a few days so much I ate carbs to make it very easy… I don’t do that anymore. If fasting is harder, I find another way to make it easy again.)
But for me, omg, being zc for years I did the total carb day and in the end I suffered for days, hell I thought I might have to go to the ER or something it was that nasty LOL
