Mushrooms are low in calories and surprisingly rich in nutrients that are hard to find in other vegetables. A one-cup serving (about 70 grams) of raw mushrooms has just 15 calories, 2 grams of protein, and 1 gram of fiber. But the real story is what mushrooms offer beyond those basic numbers: vitamin D, selenium, copper, a unique type of fiber called beta-glucan, and two powerful antioxidants found at higher levels in mushrooms than in almost any other food.
Protein and Fiber at Very Few Calories
Mushrooms are mostly water, which is why they’re so low in calories. That one-cup serving delivers its 2 grams of protein with virtually no fat and minimal carbohydrates. The protein in mushrooms contains all the essential amino acids your body needs, though the amounts are modest compared to meat or legumes. The specific amino acid profile varies by species and even by growing conditions, so no single mushroom variety stands out as a complete protein replacement. Still, mushrooms add meaningful protein to meals, especially when combined with grains or beans.
The fiber in mushrooms is different from what you get in fruits or whole grains. Much of it comes from beta-glucans, a type of soluble fiber also found in oats and barley. Oyster and shimeji mushrooms are the richest sources, containing 3.2 and 3.7 grams of beta-glucans per 100 grams of fresh mushroom, respectively. Common white button mushrooms have less, around 0.7 grams per 100 grams. To get 1 gram of beta-glucan from button mushrooms, you’d need to eat roughly 150 grams, or about six raw mushrooms. Oyster and shimeji mushrooms get you there with just 30 grams.
Mushroom cell walls also contain chitin, the same structural compound found in shrimp shells. Chitin acts as insoluble fiber, which means it passes through your digestive system largely intact. This is one reason raw mushrooms can feel tough to digest. Cooking breaks down the chitin, making the other nutrients inside the cells more accessible.
One of the Only Non-Animal Sources of Vitamin D
Mushrooms produce vitamin D2 when exposed to ultraviolet light, just as your skin produces vitamin D3 in sunlight. This makes them one of the very few non-animal, non-fortified food sources of vitamin D. The catch is that standard grocery store mushrooms are typically grown indoors in the dark, so they contain almost none. Untreated portabella mushrooms, for instance, have only about 11 IU of vitamin D2 per 100 grams.
UV-treated mushrooms are a completely different story. Portabellas exposed to UV light for just 15 to 20 seconds during processing jump to around 446 IU per 100 grams, with some producers achieving over 700 IU. Maitake mushrooms treated with a proprietary UV method have been measured at 2,242 IU per 100 grams, which far exceeds the daily recommended intake of 600 IU for most adults. Look for packaging that says “UV-treated” or “excellent source of vitamin D” if this is a nutrient you’re trying to get from food. You can also place store-bought mushrooms gill-side up in direct sunlight for 15 to 30 minutes before eating them to boost their vitamin D content at home.
Selenium and Copper Stand Out Among Minerals
The mineral profile of mushrooms isn’t evenly impressive. White button mushrooms provide more than 30% of the daily recommended intake for copper and more than 13% for selenium per serving, making these two minerals the nutritional highlights. Copper plays a role in energy production and iron metabolism, while selenium supports thyroid function and acts as an antioxidant cofactor.
Potassium, magnesium, and sodium are present but in nutritionally small amounts. White button mushrooms provide only about 3.4% of daily potassium needs per serving, despite mushrooms sometimes being promoted as a potassium source. You’d need to eat a large quantity to rival a banana or a potato. The real mineral value of mushrooms lies in their copper and selenium content, not the other minerals.
B Vitamins Across the Board
Mushrooms are a reliable source of several B vitamins, particularly riboflavin (B2), niacin (B3), and pantothenic acid (B5). These vitamins help your body convert food into energy and maintain healthy red blood cells. Crimini and portabella mushrooms tend to have higher B vitamin concentrations than white button varieties because they’re more mature forms of the same species. Shiitake and oyster mushrooms also contribute meaningfully to B vitamin intake. Because B vitamins are water-soluble, boiling mushrooms can leach some of these nutrients into the cooking liquid, so sautéing or roasting preserves more of them.
Two Antioxidants You Won’t Find Elsewhere
Mushrooms are the richest dietary source of ergothioneine, an amino acid that your body can’t produce on its own. They’re also a strong source of glutathione, often called the body’s “master antioxidant.” Both compounds help protect cells from the kind of oxidative damage linked to aging and chronic disease. What makes mushrooms unique is that they contain both at once, and in concentrations that other foods can’t match.
The levels vary dramatically by species. Porcini mushrooms contain by far the most ergothioneine at 7.27 mg per gram of dry weight. Yellow oyster mushrooms come in second at 3.94 mg/g, followed by pioppini at 2.56 mg/g. For glutathione, maitake leads at 2.41 mg/g dry weight, with pioppini and lion’s mane (sometimes sold as pom pom) close behind at 1.92 and 1.50 mg/g respectively.
Common grocery store varieties contain less of both antioxidants but still meaningful amounts. White button mushrooms have 0.41 mg/g ergothioneine and 0.63 mg/g glutathione. Crimini mushrooms are nearly identical. If you want to maximize your intake of these two compounds, specialty mushrooms like porcini, oyster, maitake, and shiitake are worth seeking out. Shiitake, increasingly available in regular supermarkets, delivers 0.92 mg/g ergothioneine and 1.14 mg/g glutathione.
How Cooking Changes the Nutrition
Cooking mushrooms doesn’t just improve their taste and texture. It breaks down the tough chitin in their cell walls, releasing nutrients that your body can’t easily access from raw mushrooms. Heat processing significantly affects the levels of water, fat, carbohydrates, and antioxidant activity in the final product, but the direction of that change depends on the cooking method.
Frying produces the highest antioxidant activity among common cooking methods, likely because the reduced water content concentrates protective compounds. It also, predictably, increases the calorie count. Boiling and stewing tend to leach water-soluble nutrients like B vitamins and potassium into the liquid, so if you’re making soup, the broth retains what the mushrooms lose. Sautéing in a small amount of fat is a practical middle ground: it breaks down chitin, preserves most nutrients, and helps your body absorb fat-soluble vitamin D.
Ergothioneine is notably heat-stable, so you won’t lose much of it regardless of how you cook your mushrooms. This is one nutrient where preparation method matters less than simply choosing a species with high levels to begin with.