Studies are increasingly indicating that almost any change you make to the diet changes your gut microbiota. Those changes might be slight, and in fact difficult to predict from person to person, but they are there.
Now new research seems to indicate that eating white button mushrooms daily can act as a prebiotic by improving the microbial community in the gut, leading to improved regulation of glucose in the liver; a finding that could one day pave way for new diabetes treatments, although one wonders why anyone would wait for Pharma to make some sort of drug out of things, when you can just eat the darn mushrooms. The researchers reported their findings in a recent issue of the Journal of Functional Foods. 
The study found that feeding white button mushrooms to mice changed the composition of their gut microbes (microbiota) to produce more short chain fatty acids, and specifically speed the conversion of one fatty acid, propionate, to another, succinate. These acids can change the expression of genes that are key to the pathway between the brain and the gut that helps manage the production of glucose, or gluconeogenesis. Consuming the mushrooms set off a chain reaction among the gut bacteria, expanding the population of Prevotella, a genus of bacteria that produces both propionate and succinate. Managing glucose better has implications for diabetes, as well as other metabolic diseases.
The mushrooms, in this case, serve as a prebiotic, which is a substance that feeds beneficial bacteria that are already existing in the gut. Probiotics are live beneficial bacteria that are introduced into the digestive system. The researchers fed the mice about a daily serving size of the mushrooms. For humans, a daily serving size would be about three ounces.
What the researchers may well have been unaware of is the prior connection between the lectin found in white button mushrooms (agaricus bisporus lectin) and it’s ability to actually induce growth of pancreatic beta-cells (the cells that produce insulin) leading to an increase in the production of insulin. In a 2012 study a significant decrease in blood glucose concentrations, an increase in glucose tolerance and expanded beta-cell mass were observed in the mushroom lectin treated mice. The expression of several insulin related genes in the pancreas were also increased in the lectin-treated mice. Their findings demonstrated that white button mushroom administration could partially reverse the impaired beta-cell growth and suggested that the mushroom lectin has therapeutic potential in preventing and/or treating diabetes.
If that wasn’t good enough, research has also shown that white button mushroom lectin appears to have a potent anti-cancer effect against cells known to induce colon cancer, actually causing the early mutated cells that are beginning to loose their healthy architecture (undifferentiated) to slowly go back to normal (re-differentiate). 
Mushrooms and lectins in general have a mixed reputation in nutritional circles. Some less sophisticated sources claim that silver dollar mushrooms can aggravate existing fungal problems such as candidiasis (they can’t) whilst others claim that lectins are destroyed by our digestion before they can exert any biological effects (most are not) or that lectins are uniformly bad for us (they are sometimes helpful, sometimes harmful, and sometimes quite innocuous).
1. Prebiotic effects of white button mushroom ( Agaricus bisporus ) feeding on succinate and intestinal gluconeogenesis in C57BL/6 mice. Journal of Functional Foods, 2018; 45: 223
2. Agaricus bisporus lectins mediates islet β-cell proliferation through regulation of cell cycle proteins. Exp Biol Med (Maywood). 2012 Mar;237(3):287-96. doi: 10.1258/ebm.2011.011251. Epub 2012 Mar 5.
3. Edible mushroom (Agaricus bisporus) lectin, which reversibly inhibits epithelial cell proliferation, blocks nuclear localization sequence-dependent nuclear protein import. J Biol Chem. 1999 Feb 19;274(8):4890-9.