Is any mushroom edible?

The yin and yang of mycophagy

Warning: This essay contains information that may cause severe anxiety in mycophiles, distress those who believe that mushroom coffee is beneficial despite tasting like dirt mixed with sadness, and smugness in people who already dislike mushrooms. The author assumes no responsibility for ruining your next pasta dish, mushroom hunting hobby, or Instagram foodie posts. A version of this was initially published in FUNGI Magazine (18:1 Spring 2025).

Some of you may well be alarmed about what you are about to read. To avoid freaking out, please read through to the end. You will be less alarmed and more educated. Many, probably all, edible mushrooms contain highly toxic molecules. The poster child is the most widely eaten wild mushroom in the world, the porcini or cepe (Boletus edulis). This prized mushroom contains phallotoxins and amatoxins — the latter responsible for the liver destruction of the death cap and destroying angels. This was demonstrated as far back as 1976. "But wait," you say, clutching your gourmet mushroom basket, "I've been eating these for years!" Keep reading before you throw your risotto out the window.

The king bolete is not alone. The apricot perfumed golden chanterelle (Cantharellus cibarius), the rosy-hued Amanita rubescens, and several other widely consumed mushrooms belong to the same "We Could Kill You But We Usually Don't" Club. We still do not know how many other mushrooms we consume contain these molecules. Nature has an ‘ornery sense of humor.

This should not be surprising. Potentially dangerous chemicals are present in all our food, even before we lace it with additives and a sprinkling of pesticides, herbicides, and insecticides. The simple potato, for example, contains glycoalkaloids that affect the heart. Much of this is concentrated in and under the skin, especially if improperly stored, when it begins to turn greenish. Outbreaks of poisoning in boarding schools in the UK have been reported because of poorly stored potatoes, although some suspected it was the mystery meat. Solanine is present in tomatoes, particularly unripe ones, so one shouldn’t overindulge in fried green tomatoes at the end of the season, as delicious as that might be.

Beans contain a host of harmful molecules, including lectins, that bind to cell surfaces and interfere with their functions. Heat inactivates these molecules, so boiling beans eliminates these toxic components. This is why the raw food movement hasn't released a best-selling cookbook called 1001 Raw Bean Recipes: Your Path to Flatulence and Mild Poisoning.

As for the brassica family of vegetables (kale, broccoli, cabbage, cauliflower, Brussels sprouts, etc.), too much of a good thing can affect your thyroid gland. For the average Joe, who has a reasonably balanced diet, this is no problem. But for food faddists, who believe that if a little is good for you, then more must be better, eating heroic amounts regularly invites problems. As you will see, the same is true for mushrooms. Many fruit seeds, such as cherries, apples, and apricots, contain cyanide, so it's best not to munch on these. Raw cashew nuts (the ones we buy have been thoroughly washed and decontaminated) and mango skin contain urushiol, the same component of poison ivy. Leaves of rhubarb are filled with oxalic acid. Nutmeg will cause hallucinations because of the myristicin, not just the alcohol in the eggnog. Cherimoya or custard apple is delicious, but beware of the seeds. They contain several potent neurotoxins. Cassava (manioc, tapioca) must be specially processed to eliminate the cyanide. If you have kidney problems, you should avoid starfruit. The latest scare is the presence of arsenic in rice. The list is endless, but you get the point.

We have learned to live with all these factors through how we grow, process, and prepare foods. Some are genetically modified to reduce the amount of toxins. These are not "Frankenfoods," but they are produced in an old-fashioned way, through careful breeding and selection. But back to our favorite mushrooms. When man-on-horseback (Tricholoma equestre=flavovirens) was declared toxic, some of the evidence was based on feeding it to mice, which caused an increase in muscle enzymes. Unfortunately, the same reaction occurs with several perfectly edible wild mushrooms, including porcini, chanterelles, and various others. This led to a reevaluation of man-on-horseback toxicity, as the significant contributing factor was the large quantities consumed—many pounds over a short period. Similar muscle destruction has been noted when large amounts of other species are consumed. As your mother hopefully taught you, everything in moderation; or if you are of a religious bent, remember that gluttony is one of the deadly sins.

As most know, morels are a particular problem, especially when eaten raw or inadequately cooked. It was highlighted in 2024 when more than 30 people became ill, and two died following a special sushi roll that featured chopped raw morels. The toxin remains unknown, and it is not mono-methyl-hydrazine. As Beug once commented, “Morels would have been classified as toxic had they not been so delicious.” On the other hand, genotoxic hydrazines in Gyromitra gigas were recently implicated in a cluster of cases of amyotrophic lateral sclerosis (Lou Garrick’s disease) in France. The oyster mushroom (Pleurotus ostreatus) contains a plethora of poisonous molecules, including orellanine, a kidney toxin, and ostreolysin, which can affect the heart. Then there is always the danger of heavy metal contamination, depending on where the mushrooms were harvested or cultivated.

For those who eat the common inky cap (Coprinopsis atramentaria), the toxin (coprine) it contains is poisonous to the testes and sperm production, in addition to its unfortunate reaction when combined with alcohol. This is not the recommended solution for birth control. A vasectomy is more reliable. To top things off, many mushrooms contain potentially mutagenic molecules, such as agaritine in Agaricus bisporus. For those who don’t recognize the name, this is the white button mushroom and its identical triplets - cremini and portobello. Sorry to disappoint you, but these are not some fancy Italian wild mushrooms; they are merely the same button mushroom with a suntan at different stages of development.

Upon learning that portobellos are just mature button mushrooms, 87% of gourmands experience an existential crisis, 12% refuse to believe it, and 1% don’t care. Studies have never shown that chronic consumption of these has led to cancer in humans.

Proponents of the medicinal value of mushrooms have adopted the strategy of pointing out the presence of various molecules thought or proposed to have health benefits in humans. These include antioxidants, phytochemicals, vitamins, and minerals. What they fail to mention or ignore is their concentration or bioavailability. In other words, is there enough to have any beneficial effect? As with toxic molecules, their mere presence in a fruiting body or mycelium is meaningless from the standpoint of human health. Only clinical studies in humans can provide adequate evidence. Remember the Instagram influencer who said reishi mushroom powder cured their anxiety, bad credit score, and ingrown toenails. Let me introduce you to the placebo effect—it's like magic, and most of us are fooled by it. But importantly, it works and makes you feel better.

Why am I not concerned about these toxins? It is for the same reason that supposedly medicinal molecules are probably inconsequential. Most are present in such minute amounts as to be physiologically and pharmacologically irrelevant. Paracelsus, also known by his real name, Philippus Aureolus Theophrastus Bombastus von Hohenheim, in the 16th Century said, “All things are poison, and nothing is without poison; only the dose makes a thing not a poison.” The same is true of a supposed medicine.

This is the yin and yang of mycophagy. The presence of both the good and the bad molecules is generally insignificant as they are present in such negligible amounts as to be biologically irrelevant. It highlights the fallacy of any claims of benefit by the medicinal advocates or the scare-mongering of the nay-sayers. With a positive identification, harvested without contamination from a pristine environment, cooked adequately, and eaten in moderation, you can forget about the chemistry, toxins, or health benefits and merely enjoy the flavor. For that, you have to thank the abundant amount of MSG (monosodium glutamate), the most essential molecule responsible for the umami of mushrooms.

After all, the savory taste of mushrooms is the bottom line of mycophagy. People have been eating mushrooms for thousands of years with no appreciable effect on mortality or longevity.

Mushroom eating, like marriage, presents a paradox: though containing both risks and rewards, countless individuals embrace it daily. And like marriage, proper preparation and care make all the difference between delight and disaster. Enjoy them and don’t worry or stress.

References

Available on request