The Big Picture The dietary guidelines advocated by the American Cancer Society and the National Cancer Institute (which generally coincide with those of most health organizations) may sound familiar: Eat plenty of fruits and vegetables. Get lots of fiber. Limit fat, especially animal fat. Go easy on meat and avoid the cured variety (they contain nitrites). If you drink alcohol, do it in moderation. Watch your total calories, and your weight. Pretty straightforward stuff.

Carotenoid Characteristics

Carotenoids, as their name suggests, are orange and red pigments in fruits and vegetables, most notably carrots and tomatoes, although they're also in everything from sweet potatoes to spinach and brussels sprouts (in the latter their distinctive color is masked by green chlorophyll).

Lycopene, a carotenoid found primarily in tomatoes, displays double the free radical-fighting activity of beta carotene, the most widely studied carotenoid. Of 72 studies looking at consumption of tomatoes or tomato-based products reviewed in the February 1999 Journal of the National Cancer Institute, almost half showed a significant reduction in one or more of a variety of cancers.

Research shows that lycopene may be best at lowering a man's risk of prostate cancer. A 1995 Harvard Medical School study (Journal of the National Cancer Institute 1995; 87: 1767-76) queried nearly 48,000 male health-care professionals about their consumption of fruits and vegetables. The only foods that reduced their risk of prostate cancer were, apparently, tomato sauce, tomatoes, pizza (tomato paste). For those who ate ten servings a week, risk dropped 45 percent; with four to seven servings, 20 percent. In animal studies lycopene decreased the number and size of mammary tumors (Eleventh International Symposium on Carotenoids, 1996).

Tomatoes are one of the richest sources of lycopene. Cooking tomatoes helps by releasing the lycopene from the plant cell walls. Also, the oil in tomato sauce enhances absorption in the stomach. Lycopene is also available in supplements.

Unreserved Resveratrol

Wine drinkers rejoiced when resveratrol, a constituent of the skin of red grapes, was found to protect their hearts (by blocking oxidation of LDL cholesterol and discouraging blood clotting). Now they have another reason to toast this potent antioxidant. When researcher John Pezzuto at the University of Illinois at Chicago screened about 1,000 plants for anticancer activity, he came up with one whose active ingredient turned out to be resveratrol. In lab tests it squelched both free radicals and inflammation, two well-known cancer inducers (Science, 6/10/97). In a study with mice, resveratrol reduced the number of skin tumors by up to 98 percent compared to control animals. Because the effective doses were high (Pezzuto estimates a person would have to quaff about five gallons of wine a day to get the equivalent) and because more than a drink or two a day may raise the risk of breast cancer, researchers don't recommend nondrinkers take up wine. But supplements of synthesized resveratrol (as well as grape juice) may help.

Fat Chance

Saturated fat is an authentic dietary villain. Aside from clogging arteries, it's a suspected contributor to several cancers, though the evidence is greater for some cancers (prostate) than for others (breast cancer)

Of the two other main categories of fats, monounsaturated and polyunsaturated, mono seems benign, if not positively protective. For example, in a study of the influence of diet on breast cancer, Greek researchers discovered that women who consumed higher amounts of olive oil (which is mostly mono) were less likely to be afflicted with breast cancer (Journal of the National Cancer Institute 1995: 87; 110-116).

When it comes to polyunsaturated fats, however, things get complicated. The fat that predominates in corn, sunflower and other vegetable oils, called omega-6, has long been associated with cancer risk in animal experiments. Likewise the type found in margarines, trans fats, which are partially saturated vegetable oils. On the other hand, the omega-3 fats called EPA and DHA, which are found primarily in deep- and cold-water fish like cod, mackerel, and halibut, protect against both heart disease and cancer. In an epidemiological study covering 24 European countries, British researchers established that mortality rates for colon and breast cancers declined as fish and fish oil consumption rose (British Journal of Cancer 1996: 74; 159-64). And Finnish scientists discovered that the breast tissue of women who had breast cancer contained significantly less DHA and EPA than the breasts of healthy women (Nutrition and Cancer 1995: 24; 151-160).

Experts believe the omega-3s' anticancer effect derives from its ability to tamp down the prostaglandins that stimulate inflammation. Chronic inflammation unleashes a steady stream of free radicals, which can damage DNA and thereby trigger cancer. Omega-3s also help the liver detoxify potentially harmful substances.

Fortunately for the fish-phobic, nonmarine sources of omega-3 fats include flaxseed and hemp oils.

Minerals to Lower Cancer Risk

n Calcium: possibly protective against colon cancer. In a recent trial (New England Journal of Medicine, 1/14/99) researchers gave people with a history of precancerous colon polyps either two 600 mg calcium tablets a day or a placebo for nine months and found fewer polyps. n Selenium: powerful antioxidant and supporter of immunity. Researchers find that cancer rates in various regions is lowered when soil and vegetables contain more selenium

In a selenium-depleted area in China afflicted with one of the highest incidences of stomach and esophageal cancer mortality in the world, scientists asked different groups to take various combinations of nutrients. After five years they found a significant reduction in the cancer rate among those who had gotten supplements of selenium, vitamin E and beta carotene (Biological Trace Element Research 1985; 7: 21-29). In the U.S. researchers studying the potential effectiveness of selenium supplementation for preventing nonmelanoma skin cancers came up with a surprise. The 200 mcg a day the subjects received for an average of 4.5 years had no impact on skin cancer but did significantly cut the rates of lung, colorectal and prostate cancers (Journal of the American Medical Association, 12/25/96).

More recently Harvard researchers determined that men with prostate cancer had much lower levels of selenium in their toenails (a measure of consumption) than healthy men (Journal of the National Cancer Institute, 8/119/98).

Cruciferous Vegetables

Cruciferous vegetables like broccoli, brussels sprouts, cauliflower and kale, have long been singled out for their association with protection against cancer. In a 1996 survey of 94 population studies and clinical trials focusing on consumption of cruciferous vegetables, 67 percent showed a reduced risk, the strongest link being with lung, stomach, colon and rectal cancers (Cancer Epidemiological Biomarkers 1996; 5: 733-748).

Scientists at Johns Hopkins showed that sulforaphane, from these plants, stimulates enzymes that help detoxify carcinogens generated in the liver. When they injected rats with a cancer-causing chemical, only 26 percent of the rodents pretreated with sulforaphane developed mammary cancer, compared to 68 percent of controls. Even animals who did come down with cancer had tumors that appeared later and smaller.

Other researchers have focused on a cruciferous-vegetable compound called indole-3-carbinol, which has proved especially effective against breast cancer cells. Recently, scientists at the University of California at Berkeley found that indole-3-carbinol, rather than acting as an anti-estrogen, (as had been thought), actually stops breast cancer cells by turning off a protein critical to their replication (Jrnal of Bio Chem, 2/13/98). Consequently, when treating certain forms of cancer, some doctors have paired indole-3-carbinol with the chemotherapy drug tamoxifen - which counteracts estrogen - and found that the combination has proven more potent than either separately.

Fiber

Several decades ago British physician Denis Burkitt proposed that the low incidence of colon cancer among native peoples in South Africa was attributable to the fact that their diet was rich in fiber. The fiber, it was hypothesized, bulked up the stool, speeding its passage through the bowel and reducing the time carcinogens contact its lining; it also helped neutralize cancer-promoting bile acids.

This concept has been backed up by numerous studies. Recently, Harvard researchers sprinkled cold water on this idea, finding that an examination of the eating habits of more than 80,000 female nurses, could find no protective effect against colon cancer or precancerous polyps from consuming fiber (NEJM, January 21, 1999). Most experts' take on this apparent refutation: Maybe the "high fiber" intake in this case wasn't high enough, and this is just one study among many.

Fighting Breast Cancer

Fiber has also been linked to reduced rates of breast cancer. At first it was thought that if fat was a breast-cancer culprit, fiber might just be a marker for a low-fat diet. But a look at Finland undermined that idea: Finnish women eat both a lot of fat and a lot of fiber, and their breast cancer rate ranks much below that in the U.S., (where we eat gobs of fat and little roughage).

Fiber helps take estrogen out of circulation as it passes through the liver, while the isoflavones in many high-fiber plants and vegetables are themselves weak estrogens, which compete for slots on breast tissue's estrogen receptors. The special fiber in flaxseed oil called lignans act against estrogen in two ways: by binding its receptors and by inhibiting the enzyme that converts other hormones into estrogen.

Fiber comes in two basic forms, insoluble (e.g., wheat bran, celery, the skins of fruits and vegetables) and soluble (e.g., oat bran, citrus fruits, beans). Until a few years ago, scientists believed that cancer protection came mainly from insoluble fiber, but that thinking has turned around.

A soluble fiber called citrus pectin has been shown to halt the tendency of prostate, lung, breast and skin cancers to metastasize, or spread (e.g., Journal of the National Cancer Institute 1995; 87: 3448-353). Typically cancer turns deadly only when it gets into the bloodstream and invades new territory. Modified citrus pectin appears to stop this aggression by preventing cancer cells from attaching to healthy tissue.

Novel Antioxidant

While the name inositol hexaphosphate (IP6) sounds like a mouthful, many of us consume mouthfuls of this natural substance every day - in foods like corn, rice, whole-grain cereals, oats and wheat.

But now scientists have isolated IP-6 and found that this powerful antioxidant can slow the destructive cellular processes that lead to tumors. In a study published in Anti-Cancer Research (Nov/Dec 1998), scientists at the University of Maryland School of Medicine demonstrated that IP-6 could shrink liver tumors in laboratory animals.

The researchers believe that IP-6 can help prevent cancer and also be useful in lowering the risk of health problems like kidney stones and heart disease. Research like this continues to expand our knowledge of how to lower the risk of cancer. In the next millennium, with more and more information making its way into the media and onto websites, our power and the responsibility to reduce our risk of cancer will continue to grow and offer new possibilities.

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