Mushrooms are nutritional powerhouses packed with vitamins, minerals and antioxidants. They are also fat-free, high in water and low in calories, making them healthy additions to a weight-loss eating plan. With more than 3,000 varieties of mushrooms, there are plenty to choose from. Some types growing in the wild are poisonous, however, so itâ€™s best to choose only those harvested by experts. Still, that leaves more than 2,000 varieties of edible mushrooms to enjoy.