In the last three years there have been two new major scientific reviews concerning the impact of medicinal mushrooms on the microbiome.
Most recently, in 2018 The Journal of Nutritional Biochemistry published a review out of Beijing Normal University called “A critical review on the impacts of Beta-Glucans on gut microbiota and human health”. To understand why this review is important, we need to understand a bit about Beta-Glucans (β-Glucans). Beta-Glucans are very specific types of polysaccharides found in the cells of yeast, algae, bacteria and especially fungi. Actually, especially medicinal mushrooms. Beta-Glucans are well represented in scientific literature, and are known to have positive impacts not only on many markers of cardiovascular disease such as cholesterol and blood sugar levels, but they’ve also been shown to be potent activators of macrophages, mononuclear cells, and neutrophils – critically important elements of our immune system. They are so effective at strengthening the immune system that they are frequently employed as adjunct therapies for both cancer and HIV/AIDS, and rightly so. I’d guess the only more potent general activator of our immune system would be Vitamin D.
Mayan mushroom statues. They liked the sun, and mushrooms. Smart people!
For perspective, most varieties of mushroom have at least 10g of Beta-Glucan per 100g of dry matter. Shiitake mushrooms have about 23g of Beta-Glucans per 100g, Maitake about 25g, Turkey Tail mushroom about 60g per 100g. Oats are often praised for their β-Glucan content, as a great reason to consume the grain. Oats sit at about 2g of Beta-Glucans per 100g of dry matter, not even close to the levels seen in medicinal mushrooms. Still, oats are hailed as being ‘heart healthy’ in great part due to this β-Glucan content.
The 2018 published review went over quite a few studies that showed Beta-Glucans elicit positive and significant changes to the microbiome when consumed regularly. Here’s an excerpt we’ll break down:
“A recent study has evaluated the in vivo effects of cereal β-glucans on gut microbiota. At 3, 6 and 7 weeks after β-glucan administration, the experimental rats showed higher Bifidobacterium and Lactobacillus availability. The results also suggest that high doses are more effective than the low doses and β-glucans derived from oats are more effective in comparison to β-glucans from the barley. In another study [a] different group of rats were given different types of oats and results of the study showed that the levels of SCFA [short chain fatty acids] were significantly increased in oats supplemented group compared to the control group, and oat β-glucans also increased the concentrations of Bifidobacteria.”
Levels of short chain fatty acids are a good measure for healthy bacteria residing in the gut, as many of them make SCFAs as a byproduct – and SCFAs are extremely beneficial for us from a metabolic standpoint. The more SCFA’s your gut is producing, the better your gut health, generally speaking. Bifidobacterium and Lactobacillus are but two strains of bacteria in our guts (albeit major ones) and are meant to serve as another marker for overall health of gut bacteria.
The tree of life as depicted in a medieval painting (it’s mushrooms!)
The review goes on to summarize some human studies:
“A clinical trial was conducted in 52 healthy volunteers to examine the effects of low dose barley β-glucans, which increased the count of Bifidobacteria significantly. Another clinical study has revealed that β-glucan-rich durum wheat flour and whole-grain barley pasta has increased the levels of Roseburia hominis, Clostridiaceae and Ruminococcus sp., and the levels of Firmicutes and Fusobacteria were lowered. The results also showed a marked increase in 2-methyl-propanoic, acetic, butyric, and propionic acids.”
Let’s put a pin in the idea that levels of Firmicutes were lowered, we’ll get back to that shortly. The acids levels that were increased are different types of short-chain fatty acids (SCFA) with various positive effects in the gut, and in this study they are meant to be biomarkers for increased health of the gut. The website Foundational Medicine Review has a great article on how critical butyric acid is for a healthy gut. From their article:
“Butyric acid is the energy source which intestinal cells prefer over others, accounting for up to 70% of the energy produced by the cells of the gut, and is critical for both maintaining and rebuilding gut health. When the microbiome is wiped out by antibiotics, for example, consuming an exogenous source of butyric acid has been shown to restore the microbiome to health in mice. While this effect is difficult to test in humans, researchers believe that butyric acid may be helpful to restore normalcy to microbiomes which have been altered by external factors. Furthermore, butyric acid contributes to microbiome health regardless of whether the microbiome has been recently damaged. The reason for this is that butyric acid acts as a chemical signaling molecule which tells the immune system of the gastrointestinal tract that all is well. When the immune cells encounter a molecule of butyric acid in the gut, they become less likely to cause inflammation and less likely to recruit other immune cells to generate inflammation.”
The Greek god Perseus was known as the bringer of mushrooms, told to have flown above Greece in his winged sandals, dropping mushroom spores over all the land.
The review goes on:
“The in vitro [laboratory] studies of different β-glucan sources revealed that it can enhance the growth of bacterial strains such as Lactobacillus acidophilus, Lactobacillus casei, Bifidobacterium animalis lactis. In yogurt, β-glucans of barley and oats are found to increase the growth and viability of B. animalis lactis. Another in vitro study found that the fermentation of oat and barley β-glucan inoculated in human faecal samples shows changes in the SCFA production and the bacterial mass.”
Simply meaning that inserting Beta-Glucans into healthy bacterial colonies greatly increases their growth.
Previous to this, the same group out of Beijing Normal University had another scientific review published in 2017 in the International Journal of Molecular Sciences, where they concluded the following about medicinal mushrooms:
“Reishi Mushroom is a frequently mentioned mushroom that has been reported to reduce obesity in mice by modulating the composition of gut microbiota. Reishi reduces body weight, inflammation, and insulin resistance in mice fed a high-fat diet. Reishi not only reverses gut dysbiosis—as indicated by the reduced Firmicutes/Bacteroidetes ratios and endotoxin-bearing Proteobacteria levels—but also alters the intestinal barrier [strength] and attenuates endotoxemia. The results confirm that Reishi can be used as a prebiotic agent to prevent gut dysbiosis and obesity-related metabolic disorders in obese individuals.”
“Turkey Tail mushroom, is a polypore mushroom. Polysaccharopeptide from Turkey Tail regulates the gut microbiota to maintain the host health. Lion’s Mane is a Chinese mushroom with nootropic [brain & mood enhancing] properties. Lion’s Mane renders changes in the composition and activity of the gastrointestinal tract microbiota that confer nutritional and health benefits to the host.”
The ancient Chinese medical text that formed the basis of Traditional Chinese Medicine, Shennong Bencao Jing, dating in the 29th century BC (5000 years ago!) praises Reishi mushrooms as the most potent medicine available and effective for treating a wide variety of conditions.
In addition to these reviews, there was a particularly well-done human study, utilizing a randomized controlled crossover design separated by 4-week washout periods worth mentioning. It found: “Supplementation of 3 g/d [high molecular weight] β-glucan increased Bacteroidetes and decreased Firmicutes abundances compared to control (P < 0.001).” – in other words, stool samples revealed Beta-Glucans increased healthy bacteria while decreasing unhealthy bacteria. They concluded “Our data suggest that consumption of [high molecular weight] β-glucan favorably alters the composition of gut microbiota and this altered microbiota profile associates with a reduction of CVD risk markers. Together, our study suggests that β-glucan induced shifts in gut microbiota in a Molecular Weight-dependent manner and that might be one of the underlying mechanisms responsible for the physiological benefits of β-glucan.”
A high ratio of Bacteroidetes to Firmicutes, which they found Beta-Glucans help with, is strongly associated with lean body mass. One study demonstrating this is “Association between body mass index and Firmicutes/Bacteroidetes ratio in an adult Ukrainian population” and it found that “The content of Firmicutes was gradually increased while the content of Bacteroidetes was decreased with increasing body mass index (BMI). The F/B ratio also raised with increasing BMI. In an unadjusted logistic regression model, F/B ratio was significantly associated with BMI (OR = 1.23, 95% CI 1,09–1,38). This association continued to be significant after adjusting for confounders such as age, sex, tobacco smoking and physical activity (OR = 1.33, 95% CI 1,11–1,60).”
Interestingly all the reviews go over the correlation between Beta-Glucan consumption and heart health, which is quite well established in the literature. The reviews and studies presented here all believe this positive change towards heart health is because of positive changes to the microbiome. Healthy gut -> healthy body -> healthy heart.
