What are the best dietary sources of ergothioneine? It isn’t made by plants or animals––only fungi, like mushrooms and certain soil bacteria. Plants can suck some up from the soil and animals who eat the plants can similarly benefit, but the highest levels by far have been reported in mushrooms. Mushrooms and tempeh—a fungi-fermented soybean cake—are the only concentrated dietary sources. As mushrooms go, shiitake and oyster mushrooms have higher levels than white button mushrooms. However, just