I think you really don't "fail" at the paleo if done right. Unfortunately this like other diets you have all these quacks that are jumping on the bandwagon, and relaying bad advice. Some people are doing paleo following say an 80/20 rule but eating clean has given their body a break from let say gluten, and then you go on a gluten binge and undo all the good you have done. If you're gluten sensitive, then gluten must be removed completely because the havoc gluten causes lasts months. That being said you still could do your cheat but not with gluten products Then there are other things like on cheat days, consuming stuff high in rancid trans fats. Well trans fats can remain in your system for up to two years from the last time you ingested. People also don't take the time to do it 100% and its hard we are humans. There are so many things that we could be allergic to, casein, nightshades, eggs, watermelon to name a few, and you don't cut those things out. Sometimes people on the paleo diet will eat more "processed" and "feedlot" meats, now they are going all this junk from the processed meat, and an imbalance of the ratio between omega3/6 is thrown way off because of feedlot meats. People need to really read a good paleo book, opt for clean single ingredient foods, 100% grass fed/grass finished meats, free range organic chickens, pastured eggs, pastured pork. the fat profiles of feedlot vs grass fed are so different!
So some people that are doing paleo eat tons of nuts/seeds (full of phytic acid and protease inhibitors, or may have a slight nut allergy), cook with any oil they find, canola/vegetable, pam spray, eat tons of feedlot meats/commercial chicken/eggs and pork products, Then if they are on the 85/15 deal, then after eating all this substandard food they go eat a big mac and fries. See, though they may have done a paleo-ish diet and then they cheat and they don't reap the benefits. They eat prepackaged paleo food (which I don't trust) if you read labels, you see that there are things that I don't think my ancestors had access to, either that or my ancestors were really in the boonies. I believe that these people may not so readily reap the benefits, and then conclude the paleo diet a failure, yet they didn't even give it a chance? Did they try to do an elimination diet, ridding themselves of all possible allergic foods? casein, gluten, nightshades, nuts (even coconut, heaven forbid!), egg, vegetables high in oxalates and waiting a month or so and reintroducing one at a time seeing if there is a adverse affect? or getting tested for such allergens? maybe they have blood glucose dysregulation and a ketogenic paleo would be better?
So... that my take on it, I doubt that illnesses caused by years of fad diets, or following the food pyramid of death, can all be undone in a few weeks or months? For example celiacs with their torn up intestines can take an average of 9.7 years of gluten free living for their intestines to be returned to "normal".
I believe the paleo is a good "template" now just adjust to for what works, but its always better to eat "real" food. I personally don't touch anything that I hadn't prepared myself (Except for these wild caught sardines from wholefoods) I ferment my own vegetables, make my own condiments mayo/ketchup/ceasar salad dressing. I don't do ketchup anymore cause I got rid of nightshades but when I did, I made my own tomato paste from organic tomatoes. I truly make everything from scratch. All my meat is grass fed organic, vegetables organic. I am a male college student most don't even know how to boil water lol. I guess I was lucky, mother was a chef and I used to help in the kitchen a lot. I know money's tight but its cheap for me to eat this way, why?I practice protein restriction, you only need 0.8g of protein per kg of body weight, then because 1 lb of grass fed ground beef cost me $6.99 from there I can get 5-6 servings, so I usually eat to animal meat proteins a day and usually and eggs in the day so that meat last me about 3 days. Still to expensive, go to grass organ meats usually less than $4.99 a lb. Best meal on the go? Avocado they don't need to be organic the skin won't let pesticides through, (carry plastic spoons/knives in your car) Don't have time to prepare food or eat that day? Sound like a good time to do an unplanned intermittent fast. (Also helps save money, if you do it 4 times that's about 52 times a year that a lot of money in your pocket :)
On a curious note, people who have eaten a junky version of paleo still reap benefits? so i guess pseudo-paleo better than the SAD diet any day