We have a forum thread about the reishi mushroom.
Concerning the possible mechanism of action of polysaccharides from a water extract of Ganoderma lucidum mycelium (WEGL), previous studies suggest that intestinal bacteria possess distinct polysaccharide preferences and that these molecules may favour the growth of specific bacterial species in the gut microbiota. Collectively, our results suggest that both WEGL and its high molecular weight polysaccharides may be used as prebiotics to reduce body weight gain, chronic inflammation and insulin resistance in obese individual.
Not that we really needed another reason to praise Reishi, but we got one anyway. Of course this was an animal-model study and further research in humans is warranted.
Paul Stamets, a well known and esteemed mycologist, answers the question of whether or not mushrooms should be eaten raw for nutritional or health benefits.
The crux of the answer is contained in the following quote but his article goes into more detail:
No, absolutely not! Raw mushrooms are largely indigestible because of their tough cell walls, mainly composed of chitin. Eating raw mushrooms can provide flavor, but not nutritional or health benefits. In some cases, eating raw mushrooms could be dangerous.