Mushrooms For Nutrition and Cancer Prevention
By Donald R. Davis, Ph.D.
Mushrooms are unusually rich in both nutrients and unusual phytochemicals that likely have many health benefits. They have been prized as food and medicine for thousands of years, especially in Asia. Besides their taste appeal, they have a long history of use in folk medicine to improve health and treat disease. Here we will discuss the nutrients in mushrooms and highlight diverse studies suggesting that regular mushroom consumption can stimulate the immune system and help prevent major types of cancer.
Mushrooms are members of the large class of fungi, which also includes truffles yeasts, and molds. Unlike plants, they don’t require sunlight. They live by decomposing organic matter, typically in soil or on old or decaying trees. In this process, they consume oxygen and produce carbon dioxide, like animals. There are an estimated 40,000 types of mushroom, about ten percent of which are considered edible. Some 200 varieties are cultivated worldwide, but only about 20 commercially.
Many Americans know only the white button mushroom. Per capita consumption in the U.S. has tripled in the last 40 years, but it remains low compared to Canada, Western Europe, and, of course, Asia. Consumption likely will increase as Americans learn more about the benefits and varieties of mushrooms. In recent years, two additional types have become widely available in the U.S., crimini or brown mushrooms and portabella mushrooms. Crimini mushrooms are closely related to white buttons and appear similar, except they have a brown color and slightly more flavor. Portabellas are crimini mushrooms that have grown to a more mature shape and larger size, about 3 or 4 inches in diameter.
Additional varieties of fresh and dried mushrooms are available in Asian food stores. These include oyster, enoki or enokitake, shiitake, maitake, king oyster, and beech or bunashimeji. Shiitake mushrooms are popular worldwide, usually prepared from the dried form, which has enhanced flavor. Their Chinese name translates as “fragrant mushroom.” In Asia mushrooms are considered both food and medicine, with a wide range of benefits. Some mushrooms are hard and inedible, such as Reishi. They are consumed as teas, extracts, or powders and used for medicinal or tonic purposes.
Nutritionally, mushrooms are extraordinarily rich, relative to the few calories in a typical portion. Two ounces of raw white button mushrooms have only 13 calories, but contain 13% to 30% of the RDAs for four vitamins and 6% to 38% of the RDAs for six trace minerals and minerals. In all, 34 of 40 measured nutrients are adequate in relation to calories. Less complete data for the mushrooms commonly limited to Asian groceries show that they are mostly similar to white buttons, but they tend to have somewhat higher amounts of selenium, copper, and riboflavin (and also more calories).
Fifty years of research have found over 200 mushrooms that contain substances that markedly inhibit cancer cells in test-tube experiments. Wikipedia, the free, online encyclopedia, highlights this research for 17 varieties, including white button. It cites over 230 references, of which show that mushrooms help stimulate immune system cells in various ways that are potentially protective against bacteria, viruses, and fungi.
Studies in mice have gone a big step further. They show that anti-cancer substances in extracts of various mushrooms are absorbed through the digestive tract and help prevent the growth of cancer cells that researchers inject into the mice. Most such studies have used mushrooms that aren’t commonly eaten by Americans. However, two recent studies used an extract of white button mushrooms.
One study in mice found that oral white button extract reduced the size of tumors from injected breast cancer cells. It limited proliferation of the cells, but didn’t kill them. In the second study the same extract inhibited tumors from two different types of prostate cancer cells. For both cell types, the oral extract reduced proliferation and also killed the cells. The researchers estimate that their doses in mice may be the human roughly 3.5 ounces of white buttons per day. They also suggest that long-term consumption of smaller amounts may be enough to prevent the beginning of breast and prostate cancers.
These ideas are consistent with two recent epidemiological studies in Asia that found reduced risk of breast cancer in women who frequently ate mushrooms. In one study, 1009 Shanghai-area women with breast cancer were compared with the same number of similar women without breast cancer. The cancer-free women reported historical consumptions of about 25% more mushrooms than the cancer patients, mostly as fresh white button and dried shiitake. Compared to non-eaters of mushrooms, the risk for breast cancer was only about one-third for those who reported average consumptions of at least 10 grams (one-third ounce) per day of fresh mushrooms. The risk was only about one-half for at least 4 grams per day of dried mushrooms. These minimums represent one mushroom per day of about 1 inch in diameter. The benefits were observed equally for pre- and post-menopausal women.
In the other study, 362 Korean breast cancer patients were compared with the same number of similar women. Again, the cancer-free women reported greater consumption of mushrooms, in this case mostly shiitake, oyster, and enoki. The reported average daily amounts were 11.4 vs. 8.4 grams per day. Compared to non-eaters of mushrooms, the risk of breast cancer was only about one sixth in post-menopausal women who reported consuming mushrooms at least three times per week or in amounts of at least 15 grams per day. The apparent benefit was smaller and less reliable for pre-menopausal women.
Although these studies adjusted for many other differences between the women (body fatness, hormone replacement therapy, etc.), the results are only suggestive. More rigorous and difficult studies are needed in which healthy women eating different amounts of mushrooms are followed for several years.
Meanwhile, we can enjoy mushrooms for their flavor, texture, and nutrients, with the reasonable hope that modest amounts will also improve our resistance to infections and reduce our risk for perhaps several types of cancer.