According to the USDA, 1 cup of white mushroom slices contains 0.7 grams of fiber, or roughly 3% of the daily value. They also have 223 milligrams of potassium minerals. You can receive 2.3 grams of total carbohydrates, 1.6 grams of net carbs, 0.2 grams of fat, and 2.2 grams of protein for the same quantity. So, you can eat up to 2-3 cups of sliced mushrooms per day.