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Mushrooms are often considered only for their culinary use because they are packed with flavour-enhancers and have gourmet appeal.
In the past, food scientists have often praised mushrooms as healthy because of what they don't contribute to the diet: they contain no cholesterol or gluten and are low in fat, sugars, sodium and calories. But that's selling mushrooms short. They are very healthy foods and could have medicinal properties, because they are good sources of protein, B-vitamins, fibre, immune-enhancing sugars found in the cell walls called beta-glucans, and other bioactive compounds.
Mushrooms have been used as medicine for centuries. In the past, most of the medicinal use of mushrooms was in Eastern cultures, while most Westerners have been sceptical of this concept. However, due to changing consumer attitudes that seems to be changing.
My laboratory has conducted a great deal of research on the lowly mushroom. We have discovered that mushrooms may be even better for health than previously known. They can be excellent sources of four key dietary micronutrients that are all known to be important to healthy ageing. We are even looking into whether some of these could be important in preventing Parkinson's and Alzheimer's disease.
Important nutrients in mushrooms include selenium, vitamin D, glutathione and ergothioneine. All are known to function as antioxidants that can mitigate oxidative stress and all are known to decline during ageing. Oxidative stress is considered the main culprit in causing the diseases of ageing, such as cancer, heart disease and dementia.
Ergothioneine, or ergo, is actually an antioxidant amino acid that was initially discovered in 1909 in ergot fungi. Amino acids are the building blocks of proteins.
Ergo is produced in nature primarily by fungi, including mushrooms. Humans cannot make it, so it must be obtained from dietary sources. There was little scientific interest in ergo until 2005, when Dirk Grundemann discovered that all mammals make a genetically coded transporter that pulls ergo into red blood cells. They then distribute ergo around the body, where it accumulates in tissues that are under the most oxidative stress. That discovery led to a significant increase in scientific inquiry about the possible role of ergo in human health.
In 2006, graduate student Joy Dubost and I discovered that edible cultivated mushrooms were an extremely rich source of ergo and contained at least 10 times the level found in any other food source. Through collaboration with John Ritchie and post-doctoral scientist Michael Kalaras, we showed that mushrooms are also a leading dietary source of glutathione, the master antioxidant in all living organisms.
I eat mushrooms, ergo I am healthy?
Our current research is centred on evaluating the potential of ergo in mushrooms to prevent or treat the neurodegenerative diseases of ageing. We based this on several intriguing studies conducted with ageing Asian populations. One study conducted showed that as people aged, the ergo content in their blood declined, which correlated with increasing cognitive impairment.
The authors suggested that a dietary deficiency of ergo might predispose individuals to neurological diseases. A recent epidemiological study conducted with over 13,000 elderly people in Japan showed that those who ate more mushrooms had less incidence of dementia.
More ergo, better health?
One important question that has always begged an answer is how much ergo is consumed in the diet by humans. A 2016 study was conducted that attempted to estimate the average ergo consumption in five countries. I used their data to calculate the estimated amount of ergo consumed per day by a 68kg person and found that it ranged from 1.1 milligrams in the US to 4.6mg per day in Italy.
We were then able to compare estimated ergo consumption against mortality rates from each country caused by common neurological diseases, including Alzheimer's, dementia, Parkinson's and multiple sclerosis. We found, in each case, a decline in the death rates with increasing estimated ergo consumption. Of course, one cannot assume a cause and effect relationship from such an exercise, but it does support our hypothesis that it may be possible to decrease the incidence of neurological diseases by increasing mushroom consumption.
If you don't eat mushrooms, how do you get your ergo?
Ergo also gets into the food chain via fungi in the soil. The fungi pass ergo to plants grown in the soil and then on to animals that consume the plants. So that depends on healthy fungal populations in agricultural soils.
This led us to consider whether ergo levels in the American diet may be harmed by modern agricultural practices that reduce fungal populations in soils. We began a collaboration with scientists at the Rodale Institute to examine this. Preliminary experiments with oats have shown that farming practices that do not require tilling resulted in significantly higher ergo levels than with conventional practices, where tillage of the soil disrupts fungal populations.
In 1928, Alexander Fleming accidentally discovered penicillin produced from a fungal contaminant in a petri dish. This discovery was pivotal to the start of a revolution in medicine that saved countless lives from bacterial infections. Perhaps fungi will be key to a more subtle, but no less important, revolution through ergo produced by mushrooms. Perhaps then we can fulfil the admonition of Hippocrates to ``let food be thy medicine''.
Robert Beelman is a professor of food science at Pennsylvania State University.