Let's also consider the other direction -- how fresh vegetables and fruit, plus whole grains, beans, nuts, seeds, and herbs improve mood, behavior, resilience. Throw in some vigorous exercise, and for most people, drugs can't do better, without the drugs' side effects and cost. For many people, switching from a standard American diet to largely those ingredients would register as changing who they are. I just finishe…
The most logical answer is this: Anything we ingest can change our personality. Whether it's for the better or worse is an opinion.
The causative nature of how ingesting A causes a personality change of type B, must be investigated experimentally. You cannot just say eating veggies improves mood. Where is your data and what do you mean by "improve"?