CACHED AWAY in the soul of every red-blooded American who fondly recalls when carnivory was a virtue and supper wasn't supper without a centerpiece of pork chops or prime ribs lies the frail hope that all the recent emphasis on fruits, grains, and vegetables, vegetables, vegetables will somehow turn out to be a terrible mistake. Abandon that hope, ye who succor it. The truth is that the more we learn about the ingredients found in fruits, vegetables, beans, and herbs, the more impressive appears the power of those compounds to retard the bodily breakdown that results in cancer and other chronic diseases. Nutritionists and epidemiologists have long observed that people who eat a plant-rich diet suffer lower rates of cancer than do meat loyalists, and now scientists are on their way to understanding why.


Beyond bearing the benefits of vitamins and fiber, plant foods are rich with chemicals that have no nutritional value and are not necessary for immediate survival yet may impede cancer at several stages in its slow, savage evolution. Most of the experiments performed so far have been done on animals or isolated cells, and no specific ingredient from fruits or vegetables has been proved in long-term human trials to prevent or arrest malignant growth. Nevertheless, we can find encouragement (or disgruntlement) in the harmony of laboratory results with the empirical studies of long-lived populations.


Just when researchers thought they had a reasonable grasp of the basic anticancer compounds found in a healthy diet, they discovered a novel pathway through which ingredients in plants may help foil disease. Scientists at Children's University Hospital in Heidelberg, Germany, recently isolated a compound called genistein from the urine of people who eat a traditional Japanese diet, heavy on soybeans and vegetables. Through petri dish experiments with a synthetic version of the chemical, they demonstrated that genistein blocks the event called angiogenesis, the growth of new blood vessels.


This talent may have significant implications for both the prevention and treatment of many types of solid tumors, including malignancies of the breast, prostate, and brain. When a tumor seeks to expand in size beyond a millimeter or two - about the dimensions of a hyphen on this page - it first must foster the growth of new capillaries around it. Once it is fully vascularized, the malignancy receives the oxygen and nourishment it needs to keep swelling, and it eventually invades the blood and lymph system and seeds fatal metastatic colonies elsewhere in the body. By inhibiting capillary growth, genistein just may keep nascent tumors from growing beyond harmless dimensions.


Genistein is found in high concentrations in soybeans and to a somewhat lesser degree in other leguminous plants. In those on a traditional Japanese diet, the urine level of genistein is at least thirty times that of Westerners. Such a diet could explain why, when Japanese men leave their country for several years to work in the United States or Europe, their rate of invasive prostate cancer rises sharply. Any tiny prostate tumors that had been kept in check by daily intake of, say, miso soup finally are free to grow once the men assume a more Western, genistein-poor culinary style. If genistein proves its mettle through testing in animals and controlled clinical trials, the compound may be useful both as a dietary measure to prevent cancer and, in concentrated form, to treat tumors already in progress.


Blocking angiogenesis is considered an ideal sort of therapy, one that can attack the malignancy while leaving normal tissue intact. Other than meeting the sinister demands of tumors, new blood vessels grow in the adult body only after fairly rare events like severe injury, heart attack, or the implantation of an embryo in the uterus; thus, any compound that impedes angiogenesis would have few side effects.


Encouraging as the findings of anticarcinogens in foods may be, researchers admit that the field of food analysis is in its infancy. Food is chemically daunting, with every stalk of broccoli or slice of melon composed of hundreds or thousands of individual yet interacting chemicals. Some plant products contain natural toxins that promote cancer along with compounds that inhibit the disease, and it can be difficult to sort out which class of chemicals predominates in a given food. Beyond its inherent difficulties, the nutrition business is prone to faddishness, charlatanism, and hype, peopled as it is with fanatical adherents of vitamin supplements, the anti-aging crowd, strict frugivores, immoderate legumivores, and the like. Mainstream researchers have tended to shy away from it.


Nor has there been much encouragement for studies focused on the prevention of cancer rather than its treatment. On average, only about 5 percent of the approximately $2) billion annual budget of the National Cancer Institute is earmarked for disease prevention; far more goes toward expensive and high-profile studies like those on gene therapy, which, if it works, will take years before it is of use to many cancer patients. The cost of bringing the widely touted drug taxol to market is estimated at $1 billion, yet taxol adds only about five months to the life of an ovarian cancer patient. Would that a similar sum were spent on preventing the cancer in the first place, a task that demands greater knowledge of the things people put in their mouths.


To be sure, some of the benefits of a plant-based diet are what it helps one avoid: a person taking in lots of fruits and vegetables is less likely to fill up on fatty foods. Moreover, vegetables have fewer calories than do meats and cheeses, and restricting calorie intake has been shown in animal studies to sharply reduce the incidence of cancer. Yet apart from the virtues of omission, the positive benefits of vegetables are many. In the course of metabolizing energy and using oxygen, the body's cells constantly generate hazardous molecules called free radicals, which can mutate genes and set the foundation for cancer. Most of the radicals are sopped up by the body's native antioxidant enzymes, but yellow and green vegetables, as well as melons and citrus fruits, also offer a wealth of antioxidant compounds, including vitamins C, E, and beta carotene, the precursor to vitamin A. Animal experiments have shown that rosemary, green tea, and curcamin - the chemical responsible for curry's yellow pigment - al suppress cancer growth, very likely by acting as antioxidants and neutralizing free radicals before they reach the cell's kingpin DNA.


Scientists have explored the influence of plant chemicals on estrogen metabolism and the ways that diet may inhibit breast cancer. It's known that estradiol, the precursor to estrogen, takes one of two metabolic pathways, turning into either a 16-hydroxylated or a 2-hydroxylated form of estrogen. The 16 form is stimulatory and has all the earmarks of being a comparatively dangerous version: women with a high risk of breast cancer show elevated levels of the :r6 type in their blood, and tissue from breast tumors contains more of the 16-hydroxylated form of estrogen than does surrounding, noncancerous breast tissue.


By contrast, the 2-hydroxylated form is relatively inert and has been found to be elevated in women who are vigorous athletes and thus have a lower than average risk of breast cancer. Of relevance to our story, the inactive type of estrogen also predominates in women who eat many cruciferous vegetables like broccoli, Brussels sprouts, and cabbage.


By isolating ingredients from these leafy green vegetables, researchers have shown that one chemical in particular, indole-3carbinol, can induce estradiol to follow the harmless metabolic route toward 2-hydroxylation. To see whether that inducement makes any difference to women's cancer risk, in mid-1993 the researchers began giving a group of women daily capsules of 400 milligrams of indole carbinol, equivalent to the amount in half a head of cabbage. Within the first few weeks of the study, the participants' blood levels of the harmless 2-hydroxylated estrogen had risen to concentrations seen in marathon runners and remained elevated for months; but whether the change in estrogen metabolism affects breast cancer rates will take years to sort out.


The cruciferous vegetables are a motherlode of anticancer compounds, each chemical displaying its own method against cell madness. Another protective ingredient is sulforaphane, the most robust member of a chemical class known as isocyothionates, which lend broccoli, cauliflower, kale, mustard, horseradish, and many other vegetables and spices their tangy snap. The isocyothionates seem to guard against cancer indirectly, by stimulating the body's production of naturally occurring protective enzymes - phase 2 enzymes - which latch on to carcinogens, detoxify them, and swiftly flush them from the body.


Scientists have been able to identify sulforaphane and other enzyme inducers in foods through a simple system that relies on cultured mouse liver cells and scans for a spike in phase z enzyme activity. Applying the screening method not only to different vegetables, but to diverse varieties of the same vegetable, they have found that the amount of inducer ingredients varies tremendously from one sample to the next, either because of natural genetic variations among strains, or because of the different methods in vegetable cultivation.


Nothing in food analysis is proving to be simple, and everything appears to do many things. Vitamin C, beyond its antioxidant muscle, also inhibits in the stomach the creation of nitrosamine, a potentially dangerous carcinogen. In addition to suppressing blood vessel growth, genistein acts directly on cancer cells and deters their proliferation. Fiber, which almost singlehandedly resuscitated the breakfast cereal industry (but also is at the heart of fruits and vegetables), exerts an array of positive effects on the body. It dilutes the concentration of noxious compounds in the colon so that the toxins have less chance of harming the delicate mucosal tissue there, and it moves everything through the system faster. Fiber also alters the environment of the gut and colon. Through a poorly understood mechanism, it discourages the growth of harmful bacteria that release enzymes believed to promote cancer by transforming precarcinogenic chemicals in food into active agents of malignancy. At the same time that it hinders undesirable microbial expansion, fiber bolsters the growth of benign bacteria, which further crowd out the unsavory strains. As though that weren't reason enough to trade chewing the fat for chewing the cud, fiber also encourages the creation of the healthier form of estrogen, and thus may impede breast cancer.


Considered together, the intricacy and synchronicity of the chemicals in plants argue firmly against an undue reliance on vitamin supplements to compensate for a rotten diet of snacks and french fries. If scientists have yet to understand all the subtleties of a Brussels sprout, how can anybody hope to recapitulate it in a pill?