I ended nearly three years of a vegetarian diet with a gyro. The only effect I suffered was not pooping the next day. I felt like myself the day after that.

I intentionally ate some cookies the other day, after avoiding gluten for nearly three months, to see just how I'd feel. I definitely felt bad for the next few days, and I recognized that it was how I had always felt being going paleo. I thought that constant mild-to-moderate cramping and heavy feeling was normal for me.

I've definitely gone more than 30 days repeatedly without having any kind of shellfish, and they never cause me trouble when I do eat them.

I don't think I react negatively to all foods I may exclude for a given amount of time.

30 days is certainly long enough to change the composition of your gut flora so that you may or may not be able to digest something you did before. It seems to me that might be a valid explanation why folks who go paleo seem to develop intolerances to foods that consumed regularly before going paleo (foods that had no prior ill effect, mind you.)

Placebo and nocebo effects probably run rampant through the paleo community as well.

I do not eat wheat, dairy or legumes and have not for years but 'once in a blue moon' I may have some if I am dining out (which is ultra rare for me) and I do not suffer any GI distress. Same with starchy carbs, I am LC-VLC but if I do decide to feast on roasted sweet potatoes I suffer no ill effects. Just my personal experience.

My experience has been that I don't necessarily have a reaction immediately. However, it takes a few exposures to the food (wheat/gluten) and my old symptoms come back.

They're not always necessarily gastric reactions either.

For me at least, it seems that dosage matters too.

Robb's addressed this topic several times, however I do think that some stuff you may have some sort of reaction that eventually goes away and other times you'll eat it and not react until some time later. N=1 experimenting isn't always the best because it all depends on the person being able to interpret their own results. Interpretation (especially when you are the scientist and the experiment) can be greatly influenced by personal bias. For a long time I've had an issue with dry itchy skin on my nose and thought it was related to dairy or bell peppers as these things seemed to make it worse. Luckily for you we have this great website that lets you compare notes. I have since discovered that dairy was not an issue and that mint in my toothpaste seems to trigger the dry itchy skin on my face. Robb's method isn't perfect but it can be effect and is cheap and easy. Think about the resistance you get just trying to get people to try paleo and then add to that additional resistance you would get by telling people they got to pay for a bunch of expensive labs and then find someone that will be able to correctly interpret them for you. We'd have very few people on paleo. You would be fine to go out and get a ton of blood work done to find out for sure what foods may be a problem but in the end may or may not tell you any more than just trying stuff and listening to you intuition and your body.

http://robbwolf.com/2011/02/22/the-paleo-solution-episode-68/

http://chriskresser.com/paleo-nerd-a-thon-with-robb-wolf-mat-lalonde

http://robbwolf.com/2010/12/07/the-paleo-solution-episode-57/

After doing it myself, there is a distinct difference between problems due to unfamiliarity and due to some other issue. When I added beans back in, I had a problem for a few hours, with wheat, it is a few days.

I don't have an answer for you but I have definitely noticed what others have: If I go wheat-free for about a week or more, re-introducing high amounts of wheat wreaks havoc on my body. I feel like crap!!!
I don't think this is a wheat-intolerance, since I am fine unless I cut out wheat completely and then try to re-introduce it. Tiny amounts are fine but having something heavy like a bagel is definitely out of the question.

Now, the REAL question is this: would the same thing happen if I went "meat-free" for a month and re-introduced meat? I don't think it would. So do I have a wheat intolerance?

My parents argue that going wheat-free is actually bad for me and I should instead go "low -wheat". This way, I won't suffer so much on the days that I do decide to increase my wheat consumption.

There's no account for the role of expectancy in these kinds of input-output questions, and yet almost certainly expectancy is a huge factor. "If I consume X for a long time, and and I feel certain effects, and then I stop consuming X for 30 days, I don't feel those effects in the same way. Lo and behold, when I begin consuming X again, I feel effects that seem consistent with the hypothesis that..."

I continue to enjoy hearing really intelligent types — experts, they assure us they are — utter this phrase with amused nonchalance that doesn't even come close to masking their hubris: "Well, you see, it was only the placebo effect. Now, let's move on to the important factor."

Whoa, wait, stop. I keep wanting to know more about that easily dismissed belief-related effect, which so often shows up in very tangible, physical forms, correlated with "mere" belief.

That one's tummy hurts 30 days later, is a given. To what extent is the hurt related to the expectation that a return to dairy will indeed cause distress? How much of the distress is explicitly a physical phenomenon.

Not easy to tease this stuff out categorically.

I think a lot of people who know they're at least a little lactose intolerant would definitely agree that it's something that varies dramatically with exposure. If I don't eat dairy for a long time, eating some definitely gives me very classic lactose-intolerance symptoms (I'm Asian, so presumably I'm predisposed). But if I eat some regularly, then I can pretty much eat as much cheese as I want to, no problem, and I find milk gross, but it won't kill me.

Also, lot of people I know who spent time living in countries where there was no dairy suddenly developed temporary lactose intolerance when they got back and re-introduced it into their diet.

I don't know the science of it, and I can't answer with relation to other food, but I definitely think it's something to consider.

If these foods are really good for you, you should be able to get right back into them within a few days. I have gone months without pretty much every food. Vegetables, meat, and fruit are all fine even after months, no problems reintroducing them. Dairy takes a few days of mild belly grumbling, and if I eat wheat I feel like I'm dying even after many days. So clearly I have some gluten issues, but probably not dairy or paleo food issues. Maybe if I had kept eating wheat every day eventually I wouldn't have had the response to it, but food that I could truly handle would have been faster.

digestive enzymes are digestive enzymes. if you eat paleo or even if you dont eat paleo they are all active. every single one of those different kinds are active. what is different is the chopped up molecules of the different foods you eat. you missed the boat entirely on the theory. while it is true that we are all born with lactase it will go down in most folks with age, and not with diet. take a look at all the known digestive enzymes and tell me of one that disappears on a paleo diet. maybe you studied starvation like myself and learned that the protease enzymes are down regulated, fine. what has starvation to do with a paleo diet?

i visited your page, you said you have irritable bowl i can assume then your gut is irritated from food that your body recognizes not as food but as a dangerous substance and uses the only tools that it has to eliminate the threat. well, for most people that threat is food that our species newly ate and not the food the species always ate. you could be different. paleo diet is a species specific cure and you are an individual. you will have to find the foods that your specific body was programed to see as a threat where as for others it still a food. Paleo is a good starting point for our species, you  on the other hand still have some work ahead of you.