In addition to being delicious, mushrooms are rich in antioxidants, the plant chemicals that may stave off cell damage. They're also stuffed with beta glucans, a type of soluble fiber that may improve immune system function and help control cholesterol levels. Studies suggest that foods rich in antioxidants and beta glucans are the foundations of a healthy diet (effects, researchers emphasize, that cannot be mimicked by taking supplements). And not only are mushrooms nutrient-rich, but these famously fun guys are high in protein while low in calories and in fat. In other words, mushrooms are a low calorie, highly nutritive food. Junk food and candy, by contrast, are highly caloric but low in nutrients.