Are Raw Mushrooms Toxic?
By Jeany Miller
Mushrooms are found throughout the world and have been a highly honored food in many cultures. For example, Ancient Egyptians considered mushrooms to be royal food, while the French harvested them in caves during the seventeenth century. Mushrooms did not achieve status in the United States until the late 1800s. Today, mushrooms are a cooking staple in many American kitchens. According to recently-analyzed nutrient data, mushrooms contain B-complex vitamins - riboflavin, niacin and pantothenic acid - as well as selenium, potassium and vitamin D. But the question still remains if raw mushrooms are toxic. While many continue to debate this, the general answer is yes, mushrooms can be toxic when eaten raw.
Mushroom Poisoning in General
According to the U.S. Food and Drug Administration (FDA), mushroom poisoning is caused by the consumption of raw or cooked species of mushrooms and toadstools. The term toadstool is commonly given to poisonous mushrooms, but individuals who are not experts in mushroom identification have no way of recognizing the differences between poisonous and non-poisonous species. Poisonings in the United States occur most commonly when hunters of wild mushrooms misidentify and consume a toxic species or when persons collect and consume a poisonous American species that closely resembles an edible wild mushroom. The FDA states that toxins involved in mushroom poisoning are produced naturally by the fungi, and each individual specimen of a toxic species should be considered equally poisonous. Mushroom poisonings are generally categorized by their physiological effects. These include:
- Protoplasmic poisons: poisons that result in generalized destruction of cells, followed by organ failure
- Neurotoxins: compounds that cause neurological symptoms such as profuse sweating, coma, convulsions, hallucination, excitement, depression and spastic colon
- Gastrointestinal irritants: compounds that produce rapid, transient nausea, vomiting, abdominal cramping and diarrhea
- Disulfiram-like toxins: non-toxic compounds that produce no symptoms unless alcohol is consumed within 72 hours after eating them
Poisonous Mushroom Varieties
The Wood Blewit mushroom is a choice species when thoroughly cooked but moderately poisonous if eaten raw. This is but one example of edible mushrooms that can be poisonous. According to experts, gastrointestinal irritants are the most common type of mushroom poisoning and the least troublesome. Mushrooms in general contain a number of proteins and amino acids. These can cause mild to severe gastrointestinal irritation, and symptoms include nausea, vomiting, diarrhea and abdominal cramps. Hemolysin is a toxin contained by certain mushroom species. This substance causes the destruction of red blood cells in the body. In addition, common button mushrooms and Portobello mushrooms contain hydrazines. These are potentially carcinogenic substances that deactivate only with cooking. One example of hydrazines is agaritine, a derivative of glutamic acid. According to researchers, agartine was found to cause cancer in mice, and is thus suspected to result in the same for humans. However, a daily intake of 10 grams of mushrooms would not result in a measurable increase of cancer among the population. Thus, although button and white mushrooms do contain toxins, they can be eaten raw (after washing) without a significant risk for poisoning. While cooking edible mushrooms is likely to prevent poisoning, another reason for heating them is to kill potential pathogenic bacteria. According to experts, mushrooms are commonly cultivated on horse manure. The manure is generally sterilized before use, but it still provides a rich medium for bacterial growth. Thus, a considerable risk exists for pathogenic bacteria to be present on raw mushrooms. Cooking destroys the bacteria and ensures that no illness is transmitted to humans.
Wild Mushrooms and Poisoning
According to the FDA, "Specific cases of mistaken mushroom identity appear frequently." For example, the Early False Morel is easily confused with the true Morel, and poisonings have occurred after consumption of fresh or cooked False Morels. Other examples of mistaken mushroom identities that cause serious poisoning are as follows:
- Death cap is often mistaken for Caesar's mushroom
- Cleft foot death cap is often mistaken for Panthercap
- Autumn skullcap is often mistaken for little brown mushrooms
Mushrooms that lead to mild gastroenteritis are quite numerous and include members of the Agaricus, Boletus and Pluteus families, as well as others. The FDA states, "Cultivated commercial mushrooms of whatever species are almost never implicated in poisoning outbreaks unless there are associated problems such as improper canning."