Mushrooms have become known as a good source of powerful nutrients, including potassium, riboflavin, niacin, selenium, ergothioneine and potassium. And did you know they are the only source of Vitamin D in the produce aisle? Mushrooms are fat-free, cholesterol-free, gluten free, low in calories and low in sodium. Fresh mushrooms can be added to many everyday dishes to provide extra nutritional value, flavor and culinary interest.