What Is the Nutritional Value of Mushrooms?

Unlike most vegetables, mushrooms are not plants but organisms classified in their own kingdom; their nutritional composition therefore differs considerably from that of fruits and vegetables. Because they contain more than 90% water, 100 g of fresh mushrooms contain only 20–25 calories, while providing B vitamins and some minerals. One of the most notable nutritional features of mushrooms is that varieties exposed to sunlight can produce vitamin D; this makes them unusual among plant-based foods. Their protein content is higher than that of vegetables but lower than that of meat, so they are generally considered a complementary protein source.

What is the nutritional composition of mushrooms?
On average, 100 g of white button mushrooms contain 22 calories, 3 g of protein, and less than 1 g of fat. They are also low in carbohydrates, so they are often chosen for low-calorie diets. They are also rich in potassium, phosphorus, and selenium; selenium is a mineral associated in particular with the immune system.

Are mushrooms a complete protein source?
Although mushrooms contain less protein than legumes, they are a notable plant-based source: 100 g provide about 3 g of protein, less than meat or eggs but more than vegetables. They are not recommended as a standalone meat substitute in a vegetarian diet. Eaten with legumes or whole grains, they complement the variety of protein sources.

How does vitamin D production happen?
Mushrooms can produce vitamin D2 when exposed to ultraviolet light, including sunlight, for a few hours before harvest. Some producers use this property to sell vitamin D-enriched mushrooms. Ordinary white button mushrooms grown in darkness have very little of this vitamin; mushrooms without a “vitamin D enriched” label on the package should not be assumed to have this feature. Mushrooms produced this way retain most of their vitamin D content during storage for a few days.

How can mushrooms fit into a diet?
Because they are low in calories and have a filling texture, mushrooms can be used as a volume-adding ingredient in dishes that replace some of the red meat, such as meatballs, sautés, and stuffed dishes. This lowers total calories while maintaining a satisfying portion. Consuming 2–3 servings a week is considered a reasonable upper limit in most dietary guidelines; mild digestive discomfort has been reported with excessive consumption of some varieties.

What should you look for when selecting and storing mushrooms?
When choosing fresh mushrooms, look for a cap that is tightly closed and a surface that is dry and free of spots. If the cap has opened and the gills are visible, the mushroom is beginning to lose freshness. A cut surface that is slightly dry rather than moist is also a sign of freshness; a wet, slippery surface is an early sign of spoilage. Store mushrooms in the refrigerator in a paper bag or a ventilated container rather than a plastic bag. A plastic bag traps moisture and can make mushrooms slimy within 1–2 days, while a paper bag absorbs excess moisture and can extend shelf life to 4–5 days. Frozen mushrooms also retain most of their nutritional value, making them a convenient option when they are out of season.

Quick summary
Mushrooms are low in calories, rich in B vitamins and selenium, and a limited but valuable source of plant-based protein. They are not a complete meat substitute, but they can play a meaningful role in a balanced diet alongside legumes and whole grains.