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Mushrooms are low-calorie food that is a good source of B vitamins and minerals. A serving of most types of mushrooms, at 3 or 3.5 ounces (about 85 or 100 grams) has only about 30 calories on average. The calories come almost completely from protein and carbohydrates and offer about 2 grams of dietary fiber. Mushrooms are typically good sources of the vitamins B1, B2, and B3. They are also good sources of the minerals potassium, copper, and selenium.
One commonly available and widely eaten mushroom is the white or button mushroom. It is typical of the nutritional value of mushrooms and is actually the same species as crimini and portabella mushrooms but picked when immature. One 3.5-ounce (100-g) serving of raw white mushrooms contains only about 20 calories and about 3 g each of protein and carbohydrates. This serving provides about 20 percent of the U.S. recommended daily allowance (RDA) for vitamins B2 and B3 and is also a fair source of B1 and B6. It is likewise a good source of potassium, copper, and selenium.
A 3-ounce (84-g) serving of brown mushrooms contains about the same amount of B vitamins as younger white mushrooms. The nutritional value of mushrooms, both white and brown, includes about 10 percent of the RDA for potassium in these servings. Both types also contain about 15 percent of the RDA for vitamin B5, which is found in many foods. Brown mushrooms, which are also called crimini mushrooms, are slightly higher in selenium. Still, all types of mushrooms are one of the better dietary sources for this mineral.
Portabella mushrooms are similarly good sources of B vitamins and minerals. A 3.5-oz (100-g) serving of grilled portabella mushroom contains only 35 calories. Grilled portabella mushrooms are sometimes eaten or served as alternatives to meats such as hamburger, which are much higher in overall calories and fats. This serving also contains 2 g of dietary fiber and about 4 g of protein. The nutritional value of mushrooms in the above serving size provides between 5 and 10 percent of the RDA for protein.
Different methods of cooking and storing can affect the nutritional value of mushrooms. Canned mushrooms are still a good source of B vitamins and minerals but often contain high amounts of added salt. Low-sodium canned mushrooms may be available in some case. Mushrooms are often fried in oil or butter, which adds calories from fat.