Mushrooms are a rich source of plant protein. They are rich in vitamins, minerals, antioxidants and polyphenols. Spanish researchers tested different cooking styles of white button, shiitake, oyster and king oyster mushrooms and found that grilling was the best way to preserve the nutrient content of all the mushrooms. It actually increased their nutritional value. Frying and boiling reduced protein and antioxidant content. Results were published in the International Journal of Food Sciences and Nutrition.