Per this article from Food Consumer written by Dr. Mercola, several studies have shown that eating probiotic foods increased brain activity. In addition, certain good bacteria reduced anxiety and stressed induced hormones. The best way to activate the good bacteria is to avoid processed foods and excess sugars, while eating plant-based foods with a specific focus on fermented vegetables. Tempeh is an example of a fermented tofu product. Further research also indicates that the micro-flora in the gut may also affect brain development over time.
Eating plant-based foods has so many benefits and impacts all of the systems within the body, chief among them is the health of the gut which can lead to a positive state of mind!