I searched for some foods to increase Indole-3 Proprionate and this page is pretty good. [1] It tells what to eat (fermented foods, fiber, sprouted seeds) and what to avoid (sugar, simple starches, omega-6-heavy oils). It also introduced me to fermented bean curd. Can't want to try it.
[1] https://go.ixcela.com/metabolite-library/ipa