With one day of including any of the off limits foods I didn't notice any significant changes, other than snoring after I consume dairy. Perhaps multiple days would make symptoms worse. Still, I'm not going to make any of the foods a regular part of my diet. After the Whole30 I feel amazing, and I know it's because I've kept a lot of junk out of my body. It's probably more dangerous for me to add in these foods than for people who have strong, specific reactions to certain food groups, because if I don't immediately feel the negative effect of the food I'm more likely to keep eating it. Gradually I'd feel like crap again and probably wouldn't even notice until I did another Whole 30.