While it is possible to eat raw portobello mushrooms, Dr. Andrew Weil advises against eating any mushrooms without cooking them first. Raw mushrooms contain potentially harmful and toxic carcinogens.
According Dr. Weil, mushrooms have a tough outer wall and are difficult to digest if not cooked. Cooking mushrooms also releases key nutrients like B vitamins, minerals, and proteins.
Dr. Weil states that cooking any mushroom at a high temperature prior to eating, whether by sauteeing, broiling or grilling, helps to break down many of the potentially harmful toxins. Broiling and grilling are often considered the best ways to cook mushrooms.