NUTRITION SCIENCE NEWS
August 1999

"Cancer Prevention Diet" by Jill E. Stansbury, N.D.
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The potential of protective phytochemicals
Many people's lives have been touched in some way by cancer. Maybe they've lost a relative, a friend or an acquaintance; maybe they had a scare as a result of an annual physical. Regardless of what drives your customers to ask about cancer prevention, it is a perfect opportunity to discuss diet and supplements.

Cancer is a prominent killer of Americans--second only to heart disease--and responsible for more than a half million deaths yearly. The good news is that scientific validation for the protective power of food is accumulating. And empowering people to preserve their health through daily choices puts responsibility in patients' hands.

So where do you start? A dizzying amount of information exists on cancer-preventive food and supplements. The easiest step people can take is to modify their diets. By eating a rainbow of food colors or by emphasizing certain food groups, people will incorporate a variety of protective phytochemicals into their diets.

We are exposed to oxidizing- and cancer-producing substances daily, but compounds found in vegetables help limit the free radical initiation and DNA damage caused by these carcinogens and therefore appear to lower the incidence of various types of cancer.1,2

A Rainbow of Protection
Pigmented plant compounds appear to be important anti-inflammatories and antioxidants, and people who eat more of them have a decreased risk of cancer. Plant pigments are mostly polyphenolic, meaning they are multiphenol-containing molecules, and include chlorophyll, carotenoids and bioflavonoids.

Green plants contain particularly large amounts of chlorophyll, which is a detoxifier and possibly an anticancer agent.3 Foods rich in chlorophyll include chlorella and other blue-green algae, beet greens, bok choy, collards, dandelion greens, kale, mustard greens and nettles. These greens--among the most nutritious of all plants or plant parts--also contain other diverse nutrients and healthy constituents.4 The blue-green algae family has a high chlorophyll content and has been credited with immune-enhancing effects including stimulation of phagocytosis and enhanced response to tumors and microbes. Chlorella powder, specifically, may reduce side effects of chemotherapy for some patients and may possess direct anticancer activities.5

Orange, yellow and red-orange foods are rich in carotenoids such as beta-carotene, lutein and lycopene. These constituents are antioxidants and anticancer agents due to several different mechanisms.6,7

More than 600 carotenoids occur naturally, but carotenes are the most widely known. Carotenes seem to offer protection against lung, colorectal, breast, uterine and prostate cancers.8 Carotenes, which destroy oxygen free radicals in lipids, enhance immune response and protect cells against UV radiation.9 Foods rich in these flavonoids include apricots, carrots, citrus fruits, squash and tomatoes in addition to many green foods.

The anthocyanidins are a type of complex flavonoid that produce blue, purple or red colors. Foods rich in these phytochemicals include beets, blackberries, blueberries, cherries, purple and red grapes, and purple cabbage. Anthocyanidins support connective tissue regeneration and are anti-inflammatory; they promote blood flow and reduce cholesterol, in addition to being antioxidants.10 Anthocyanidins seem to stabilize and protect capillaries from oxidative damage11 and have been shown to stabilize connective tissue, promote collagen formation, improve microcirculation and help protect blood vessels from oxidative damage.12,13 Thus, by eating these antioxidant pigments, some believe cancer risk can be reduced because the antioxidants protect against damage and help repair connective and vascular tissues.

Procyanidins are the precursors to anthocyanidins, and are comprised of smaller units including catechins and epicatechins. Catechins are simple flavonoids that are abundant in green tea. Several Japanese studies show that tea consumption is protective against breast and other types of cancer.14,15

Phytochemical Defense
Detoxifying, stimulating and spicy sulfur compounds are present in a variety of colorful foods including broccoli, garlic and pineapple. Sulfur-containing compounds in plants are believed active, or at least protective, against cancer because many pathogens are deterred by sulfur.

The crucifer family--which includes broccoli, brussel sprouts, cabbage, cauliflower, mustard greens, radishes and turnips--has many sulfur-containing compounds as well as indoles, a subclass of phytonutrients that binds chemical carcinogens and activates detoxification enzymes, mostly in the gastrointestinal tract.16 Indoles and related compounds may promote metabolism of carcinogens17 as well as improve estrogen balance, which could reduce the risk of estrogen-related cancers such as breast cancer.18

The lily family includes garlic (Allium sativum) and onions (A. cepa), both of which also contain sulfur compounds. Studies have shown the sulfur compounds diallyl disulphide and diallyl trisulfide--two of the active agents in garlic oil--and S-allyl cysteine--found in crushed garlic--to inhibit tumor metabolism and enhance immune response.19-21 Allyl sulfides also enhance glutathione S-transferase enzyme systems, which are biochemical pathways involved in the liver's detoxification of carcinogenic substances. Allium species also have immune-enhancing actions that include promotion of lymphocyte synthesis, cytokine release, phagocytosis and natural killer-cell activity.22

Several animal studies have shown that garlic and onions prevent cancer and inhibit the progression of existing cancers, especially stomach and gastrointestinal cancers.23 Garlic appears particularly effective in reducing the risk of N-nitroso-induced cancers.24 N-nitroso compounds, also known as nitrosamines, are potent carcinogens formed within the intestines as a result of bacterial degradation of nitrates and nitrites, two common food chemicals used in the processing of ham, sausages and other meat products.

All forms of garlic have been shown to have some medicinal activity. Which one is best or most effective remains to be proven. Different forms may be better suited for some people.

Pineapples contain bromelain, a sulfur-rich proteolytic enzyme that has been investigated for antitumor effects. U.S. and French research shows oral bromelain can reduce cancer in animals. Some documented cases show cancerous tumors regressing as a result of bromelain therapy. Bromelain may also have antimetastatic effects. It has been examined in vitro to both oppose leukemia by promoting the normalization of blood cells and to reduce metastasis in lung-cancer cells.25,26

Other protective phytochemicals include the caffeic, ferulic and ellagic acids, which have been shown to degrade carcinogenic substances.27 Among other things, caffeic acid helps degrade carcinogens, and ferulic acid helps prevent nitrates in the digestive tract from being converted into the carcinogenic nitrosamines. Caffeic and ferulic acids are found in green tea. Ellagic acid, which is particularly plentiful in pomegranates, also prevents carcinogen oxidation of cellular membranes. Ellagic acid is also found in blueberries, grapes, raspberries and strawberries.28

Limonene is a bioflavonoid substance found in citrus rinds that stimulates both the glutathione transferase and the cytochrome p-450 detoxification systems.29 These enzymatic liver reactions break down carcinogenic substances in the body and help prevent them from damaging cellular DNA. Another bioflavonoid, quercitin, is ubiquitous in higher plants and has been widely studied for its antioxidant and concommitant anticancer actions.30

Unexpected Allies
Whole-grain foods, rather than those derived from processed grains, are also worth emphasizing. Whole grains contain essential fatty acids (EFAs), which serve as precursors to prostaglandins and are important components of cell membranes.

Lignans, prominent in the woody parts of plants, are found primarily in rye and flax. They are believed to be converted by intestinal bacteria into enterolactone and enterodiol, which are absorbed across the intestinal walls where they travel to tissues and blood, binding with hormonal receptors. Like soy isoflavones, these weak estrogens may reduce excessive hormonal stimulation in tissues and reduce estrogen-related cancers.31 Fiber is also thought to reduce cancer risk by binding carcinogens in the intestines and making a favorable environment for beneficial bacterial flora. Fiber is acted upon by intestinal enzymes and microbes, yielding short chain fatty acids (SCFAs), which are noted to have anticancer effects.32

Legumes--especially soybeans--are another source of anticancer fiber, phytoestrogens, lignans and saponins.33 Whether soy is a unique superfood or is simply the best-studied legume remains to be seen. Soy also contains the isoflavones genistein and daidzein, which have been found to protect against estrogen-related cancers in numerous animal and epidemiological studies.34 Soy contains protease inhibitors that may inhibit the proliferation of cancer cells.26 Genistein in soy and in red clover diminishes the growth of new blood vessels in cancerous tissues.35

Antitumor and anticancer properties also have been studied in mushrooms. Shiitake (Lentinus edodes) and reishi (Ganoderma ludidum) have been found to have general anticancer and immune-stimulating activity.36 Lentinan in shiitake mushrooms has been shown to be a potent immune potentiator.37 Maitake (Grifolia frondosa) also contains immune-stimulating polysaccharides. In a study by Hiroaki Namba, Ph.D., of Japan, mice were fed either a control diet, a diet that included 20 percent maitake powder or a control diet plus injections of maitake D-fraction extract at a rate of 1 mg/kg of body weight. Results showed that maitake inhibited metastasis by 81.3 percent in the maitake-fed group and by 91.3 percent in the D-fraction injection group.38

Kelp and seaweed are also anticancer agents, rich in the mucilagenous alginates, which, like most fibers, gums and mucilages, swell in the intestines and absorb liquid as well as toxins and heavy metals.39 Alginates also may stimulate T cell production and function since numerous other mucopolysaccharides have been shown to do this. Japanese studies show regular consumption of kelp reduces breast cancer risk.40 Kelp extracts have been highly successful in inhibiting laboratory cancer strains.41

Another place your customers may not expect to find cancer protection is on their spice rack. Cayenne pepper, ginger,42 rosemary,43 sage, thyme, turmeric44 and many others have anti-inflammatory, anticancer, immune-stimulating and antioxidant properties. Research suggests that curcumin, the bright yellow flavonoid present in turmeric (Curcuma longa) roots, selectively inhibits thromboxane production while sparing prostacyclin.45,46 Thromboxane is a potent inflammatory compound produced by the body in response to injury or irritation. It causes blood vessels to constrict and the blood to clot, while prostacyclin is an inflammatory mediator that can respond to tissue injury without leading to further inflammation. Inhibiting thromboxane prevents excessive inflammatory response and reduces damage to vascular endothelia. Curcumin has also been shown to inhibit tobacco smoke mutagenicity,47 suggesting it may help protect the vascular endothelia from damage caused by smoking.

Anticancer agents can be found in the supplements section as well as at the local produce stand. By emphasizing fresh fruits and vegetables of all colors, customers can reduce their risk of cancer and many other diseases.

Jill E. Stansbury, N.D., maintains a private practice in Battleground, Wash., where she specializes in botanical and natural therapies. She heads the botanical medicine department at the National College of Naturopathic Medicine in Portland, Ore.

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