Portobello Mushrooms: Positive and Negative Effects

In 2017, the mycologist Paul Stamets was featured on Joe Rogan’s podcast to discuss the medical potential of various fungi. At one point, the conversation turned to portobello mushrooms and Stamets said cryptically, “portobellos have a problem.” When asked specifically about the negative effects of portobello mushrooms, Stamets replied “this is an explosive area of conversation, and it puts my life in danger. So, I reserve the right not to answer your question”. Rogan declined to ask Stamets further questions, but notably told his audience “anybody who’s interested, just, Google that and get back to me”. This led to widespread speculation and internet controversy over the potential harms of portobello mushrooms for human health. In this article, we examine the basis of these claims and critically assess their merit in light of current evidence.
Faith Wershba

Faith Wershba

Postgraduate researcher at the University of Cambridge.

A blue image with text saying "Portobello mushrooms"

Main takeaway: portobello mushrooms are safe to eat

There is extremely limited evidence demonstrating any adverse effects of consuming portobello mushrooms. While uncooked portobello mushrooms may contain a mycotoxin called agaritine, the quantity of this compound in a typical serving of mushrooms is relatively low and the molecule breaks down readily when mushrooms are cooked. Furthermore, human toxicological studies on the effects of agaritine have not been conducted, which limits the generalizability of scientific claims. To date, studies claiming that agaritine may be carcinogenic have been conducted in animal models using pure agaritine extract at extremely high concentrations. All this being said, eating portobello mushrooms does not have zero risk: for example, individuals with fungal allergies or high uric acid levels may want to be mindful of their portobello consumption.

Portobello mushrooms

What are the health benefits of portobello mushrooms?

Portobello mushrooms have a fairly favorable nutritional profile. They are high in dietary fiber and contain essential vitamins, minerals, amino acids, and antioxidants [2].

Specifically, portobello mushrooms are high in selenium, which has been linked to improved immune function and protection against oxidative stress [3]. For vegetarians and vegans, portobello mushrooms are also a valuable source of plant-based protein, B vitamins, and vitamin D [2].

Specifically, portobello mushrooms are high in selenium, which has been linked to improved immune function and protection against oxidative stress [3]. For vegetarians and vegans, portobello mushrooms are also a valuable source of plant-based protein, B vitamins, and vitamin D [2].

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In a mouse model, high consumption of portobello mushrooms was linked to health benefits such as reduced inflammation, lower LDL (so-called “bad”) cholesterol, and improved lipid profiles, which are important factors in atherosclerosis and heart disease [4]. The savory taste and meaty texture of portobello mushrooms makes them a popular alternative for meat products. Reducing meat consumption can be beneficial both for human health and for the environment [5].

Benefits of portobello mushrooms

Portobello mushrooms are high in fiber, vitamins, minerals, amino acids, and antioxidants. For vegetarians and vegans, they are a valuable source of protein, B vitamins, and vitamin D, nutrients which may be lacking from a plant-based diet. Animal studies have linked portobello mushroom consumption with lower inflammation and LDL cholesterol, which may indicate benefits related to prevention of atherosclerosis and heart disease. Lastly, portobello mushrooms may help reduce meat consumption and yield environmental benefits.

What are the negative effects of portobello mushrooms?

There is limited evidence to support the claim that portobello mushrooms have a negative impact on human health. However, like any food, portobello mushrooms can potentially cause issues if consumed in excessive amounts or for individuals with particular health conditions. There are a few features of portobello mushrooms that might make them problematic in specific cases.

  • Moderately high in purines. Purines are a kind of nucleobase, which serve as the building blocks for DNA and are found in plant and animal cells [6]. Purines are naturally occurring compounds and important for a variety of biological processes. However, for individuals prone to kidney stones and gout, excessive consumption of purines can be problematic. This is because purines are decomposed into uric acid, which can form crystallized deposits in the joints and/or lead to the formation of kidney stones [7]. Thus, individuals predisposed to gout or kidney stones should be mindful when consuming high-purine foods, which might include portobello mushrooms. However, it is worth noting that plant-derived purines differ from animal-derived purines, and some sources say that even high-purine vegetables such as mushrooms may be safe for individuals predisposed to high uric acid levels [8].
  • Contain agaritine. Raw mushrooms contain a compound called agaritine, which is considered a mycotoxin and potential carcinogen [9]. However, the agaritine content of mushrooms decreases significantly when cooked; for example, one study showed that 20-25% of the total agaritine content degraded after boiling for 5 minutes, and after 2 hours of cooking only 10% of the original agaritine content remained [9]. As such, consuming cooked portobello mushrooms is unlikely to pose risks of carcinogenicity. Additionally, the quantity of raw mushrooms that one would need to consume in order to ingest potentially toxic levels of agaritine would likely be extremely high. In mouse studies, significantly increased mutagenesis was observed only in mice fed relatively high concentrations of pure agaritine rather than those fed mushroom-rich diets [10]. Currently, available evidence suggests that there is no realistic risk of toxicity for humans consuming raw mushrooms [9].
  • Allergic reactions. Although allergies to portobello mushrooms are not common, there have been reports of individuals having allergic responses following consumption or skin contact with mushrooms. Adverse reactions to mushrooms often occur due to cross-reactivity against other fungal allergens, such as mold spores. Symptoms of fungal allergy can include skin itching, redness, rash, swelling, coughing, wheezing, shortness of breath and, in extreme cases, anaphylaxis [11, 12, 13, 14, 15]. It is important to note that the studies cited here cover a variety of culinary mushrooms and do not mention portobello mushrooms specifically as a cause of allergy.

Research on the effects of portobello mushrooms

Currently, there is very little evidence to support the claim that portobello mushrooms have negative health impacts. One study found that mice fed high amounts of portobello mushrooms increased concentrations of plasma bilirubin, indicating potential reductions in liver function [16]. However, no pathological changes were observed and such findings have not been replicated in a human context. Thus, there is currently insufficient evidence to support any link between portobello mushroom consumption and adverse health impacts.

Conclusion

Are portobello mushrooms safe to eat?

Overall, consumption of portobello mushrooms is safe for the majority of individuals. Moreover, portobellos can be a valuable source of protein, vitamins, and minerals in a plant-based diet and serve as a tasty alternative to meat products. Certain individuals, such as those predisposed to gout, kidney stones, or fungal allergies, may want to be mindful of their portobello mushroom intake. However, in most cases, there is no need to worry about eating portobello mushrooms. It is essential to approach claims regarding human health and nutrition with a critical eye and examine whether such internet claims are substantiated by current evidence.

Faith Wershba

Faith Wershba

Faith obtained her Honour’s Bachelor Degree in Human Biology, Immunology and History & Philosophy of Science at the University of Toronto. Currently, she is a postgraduate researcher at the University of Cambridge, focusing on the philosophy of medicine, science, biomedical research methods, and bioethics.