White mushrooms

A white mushroom is not a plant. It is a fungus, and a protein study found that animals and fungi are each other’s closest relatives, with plants on a separate branch. The white button, the brown cremini and the large portobello are one species, Agaricus bisporus: white and brown forms, picked young or left to grow. A raw white mushroom is about 92% water.

A fresh white mushroom holds almost no vitamin D, about 0.2 µg per 100 g. It does hold ergosterol, which turns into vitamin D2 under UV light, so some growers expose mushrooms to UV after harvest. In trials, UV-exposed mushrooms raised the D2 form of vitamin D in blood but lowered the D3 form, so total vitamin D did not always rise.

Mushrooms are also the highest dietary source of ergothioneine, a sulfur-containing antioxidant, and 100 g a day of white button mushrooms doubled blood levels in one study. Raw button mushrooms hold agaritine, a natural compound that may be a weak carcinogen in mice, and storage and cooking lower it. Many of the cohort studies below ask about mushrooms in general, so each card says when that is the case.

Health benefits of white mushrooms

• ★★Mixed effects on vitamin D levelsUV-exposed mushrooms raised blood vitamin D by 15.2 nmol/L in European trials, but not in US trials. A vitamin D2 mushroom product did not keep 436 older adults’ levels up through winter.
• ★★Slightly lower fasting blood sugarIn 60 adults, 84 g a day of mushrooms added to a Mediterranean-style diet for 8 weeks lowered fasting blood sugar by 2.9 mg/dL. The mushrooms were white button and oyster, and no other measure clearly changed.
• ★More weight lost when mushrooms replaced red meatIn 73 obese adults on a weight-loss plan, replacing red meat with mushrooms for a year helped them lose about 7 lb (3.6%) more. The trial cannot separate mushrooms from eating less meat.
• ★Less hungry and fuller after mushrooms than meatIn 32 healthy adults, a breakfast of 226 g of Agaricus bisporus mushrooms left people less hungry and more full than 28 g of meat. The differences were small, and they ate the same amount later.
• ★No clear change in flu vaccine responseIn 85 adults aged 60 and over, 8 weeks of Agaricus bisporus powder (5 g a day) did not significantly change the flu vaccine response. IgM antibodies rose 73% more with mushrooms, but not significantly.

Who should be careful with white mushrooms

Most people can eat white mushrooms freely. Take a little care if one of these applies:

• Eating them raw. Raw button mushrooms contain agaritine, a potential weak carcinogen in mice. A review estimated the added lifetime cancer risk in people at about 1 in 100,000 and advised avoiding them raw or poorly cooked. The risk looks small, and in lab tests cooking and storage cut agaritine.
• Irritable bowel syndrome. Monash University lists mushrooms among foods with polyols such as mannitol, which can trigger symptoms in some people with IBS. Check your serving in the Monash FODMAP app.
• Wild mushrooms. The deadly death cap has been mistaken for this species. Buy mushrooms from a shop unless an expert has identified them.

How to choose, store and eat white mushrooms

• Cooked: in lab tests frying cut agaritine by 35 to 70% and microwaving left about a third, though cooking also lost some vitamin D2 from UV-treated mushrooms in one trial.
• UV-exposed: in one trial only 67% of mushrooms grown to hold vitamin D2 actually did, so look for a label that states the vitamin D amount.
• Amounts in trials: 84 g a day (a little over a cup) for 8 weeks lowered fasting blood sugar, and 100 g a day for 16 weeks doubled blood ergothioneine.

Pick mushrooms with caps closed around the stem or only partly open, with pink or light tan gills, and keep them in the fridge in a paper bag for up to about 3 days, because plastic traps moisture that spoils them. Residues are no reason to skip them: in USDA tests of 707 mushroom samples for its 2022 report, none had a residue above the legal limit.

History of white mushrooms

In the wild, Agaricus bisporus grows in grasslands and leaf litter across Eurasia and North America. Its genome holds a large set of enzymes that break down plant matter, including lignin, which helps it live on decaying material. Genetic studies trace the species back millions of years: one puts its origin in Europe about 4.6 million years ago, and another dates a split into varieties to about 2 million years ago.

People have grown it for only a few centuries. A genome study calls its cultivation history around 300 years, and Wikipedia credits Joseph Pitton de Tournefort with the earliest scientific description of commercial growing, in 1707. The white form is still called champignon de Paris in French.

Paris growers moved into the limestone quarries beneath the city. AFP reports about 250 growers there by the late 19th century, drawn to a “royal” variety that Louis XIV had made popular by having it grown at Versailles. City growth and the building of the Metro pushed them out from the early 1900s. Around 50 were left in the 1970s, and five traditional producers remain after cheaper imports took over.

Growing got more reliable in 1893, when the Pasteur Institute in Paris produced sterilized pure-culture spawn, the mushroom’s “seed,” to grow on composted horse manure.

The white color began as a lucky mutation. A white variety turned up in 1925 at the Keystone Mushroom Farm in Coatesville, Pennsylvania, owned by the mycologist Louis Ferdinand Lambert, and most cream-colored store mushrooms descend from it. A 2026 genome study of 482 strains found that the white cap was the key trait people selected as they domesticated the species.

Emil Imbach gave the species its current name, Agaricus bisporus, in 1946. Wikipedia lists it as cultivated in at least seventy countries, and in 2022 China produced about 94% of the world’s mushrooms and truffles.