Maitake (Grifola frondosa)

What it is: Clusters of this mushroom, which resembles butterflies in flight, grow at the base of trees. This Japanese native's popularity stems from its appealing taste and its reputation for potent healing. Some foragers have lugged home maitake weighing 50 pounds, but most are far smaller (though still impressive)—about the size of a watermelon.

How it works: As with other medicinal mushrooms, maitake contains complex carbohydrates, known as polysaccharides, that increase the immune system's vigilance against potential infecting agents. A polysaccharide unique to maitake, called maitake D-fraction, interests cancer researchers: Although it doesn't seem to kill cancer cells directly, it does stimulate immune cells that fight off cancerous cells, notably for lung, liver, and breast cancers (Alternative Medicine Review, 2002, vol. 7, no. 3).

Maitake's immune-system effects also garner scientific attention. In one long-term trial involving 35 HIV-positive people, 20 patients taking maitake daily for one year showed increases in their CD4+ counts (the immune cells that get wiped out by HIV), and 85 percent of them reported an increase in general wellness, with fewer opportunistic infections (Mycoscience, 2000, vol. 41, no. 4).

Side effects: None. Eat maitake as a food or take as a supplement; 3—7 grams a day support general well-being and immune function.

Reishi (Ganoderma lucidum)

What it is: This shiny reddish mushroom, sometimes called lingzhi, grows wild in China but is cultivated all over the world.

How it works: Traditional Chinese Medicine has employed reishi as an adaptogen, or general tonic, for more than 3,000 years. In addition to boosting immunity, this mushroom seems to benefit cardiovascular health. In a double-blind trial, 18 participants who took reishi for just four weeks tended to experience a drop in cholesterol levels (British Journal of Nutrition, 2004, vol. 91, no. 2). This effect likely is due to beta-glucan, a compound that surrounds cholesterol in the small intestine, preventing its absorption (American Journal of Clinical Nutrition, 2006, vol. 83, no. 3).

Reishi also demonstrates promise in lowering blood sugar levels (important for diabetics) and in helping the body fight off infection from viruses, such as the flu, herpes simplex, and HIV (Food Technology and Biotechnology, 2006, vol. 44, no. 3).

Side effects: A rare few people taking reishi develop dizziness, dry mouth, or upset stomach. An effective dose for supporting the immune system and general health is 2—8 grams a day.

What it is: Native to Asia, this mushroom now grows around the world. A potent extract derived from shiitake, LEM (lentinus edodes mycelium), comes from the underground part of the mushroom and is harvested before the cap grows above ground.

How it works: LEM works against viruses, including HIV; strongly enhances the immune system; and inhibits tumor growth (International Immunopharmacology, 2005, vol. 5, no. 5). Shiitake also supports heart health by preventing blood platelets from becoming too sticky and clumping together (Biofactors, 2004, vol. 22, nos. 1—4).

Another shiitake-derived extract, called AHCC (active hexose-correlated compound), increases the activity of natural killer cells, white blood cells that target and eliminate tumor cells and a wide variety of infectious agents, including the flu (Journal of Nutrition, 2006, vol. 136, no. 11).

Side effects: Eating more than 5—15 grams of shiitake daily could cause diarrhea. Take 2—9 grams LEM per day. AHCC boosts the immune system in amounts of 500—1,000 mg daily.