I've noticed something about myself:
I tend to feel pretty much the same regardless of what I eat.
If I don't eat fresh fruits & vegetables much, I start really missing and craving them; but other than that, I don't feel very different whether I eat mostly Paleo, mostly Zone, mostly vegetarian, or just a little-more-healthy "normal" diet. I don't feel different whether I do or do not consume dairy products or gluten.
The only thing I've ever had issues with was an artificially-sweetened protein powder that, after a few weeks of making smoothies from it, began making my lips and mouth swell when I drank it.
I also don't drop weight very quickly when I cut calories or change my diet or increase my exercise.
I read on here about people feeling drastically better from seemingly minor diet changes and wonder if something's really screwed up in my system or if I'm just fairly lucky...