The sheer amount of changes that occur on a plant-based diet are too numerous for me to be able to pinpoint any specific thing. It wouldn’t surprise me if I do get more vitamin a these days, as well as quite a few other important micronutrients that I may or may not have been low on.
And that’s not even getting into the vast topic of phytonutrients.
Would you care to elaborate on what you feel like when you try living on plants? What do you tend to eat? How long does it take before you start feeling like shit?
Judging by your last comment about it “not hitting the same” my initial thought is that the issue might not even be nutritional, possibly more psychological/subjective.