Scientists are ever searching for foods that might thwart cancer, either by blocking development of a tumor or by slowing its growth. Just as foods can harbor cancer-causing agents, such as pesticides, some also possess natural substances that are antagonistic to cancer. The trick is discovering which foods are potentially anticancer. In this pursuit, scientists design elaborate analyses of diet and cancer connections, called epidemiology studies. They also test the anticancer powers of food and food constituents in cell cultures and animals, theorizing that the cancer-blockers may do the same in humans. The search is decidedly complex. Often investigators do not understand why a food appears to have anticancer powers or the amount needed for protection. But fascinating clues come along regularly. Here are some of the latest: Garlic and onions: Chinese who eat about three ounces of garlic, onions, scallions and leeks every day are only 40 percent as likely to develop stomach cancer as those who eat only an ounce of the allium vegetables daily. That's what a group of National Cancer Institute and Chinese scientists found in Shandong Province, a region of China known for its high stomach cancer rates. Since this is the first human confirmation of the possible anticancer properties of garlic and onions, researchers say, "It's an exciting lead, but far from definitive." But the new finding does back up animal studies showing that both onion and garlic extracts and oils can suppress the formation, growth and proliferation of several types of tumors. Dr. Michael Wargovich at the M.D. Anderson Hospital and Tumor Institute in Houston, for example, found that garlic and onion compounds saved mice from colon cancer by blocking the conversion of chemicals to powerful carcinogens. Cabbage: Studies dating back to the 1950s designate this cruciferous vegetable as a potential superstar in an anticancer diet, especially against colon and stomach cancer. Two new findings boost cabbage's reputation. One study, in another Chinese province, revealed that consumers of the most spinach, squash, eggplant, green beans and particularly cabbage had a lower risk of stomach cancer. The protective effects showed up in those who on average ate a mere 2 1/2 tablespoons of cooked Chinese cabbage a day. Also, investigators at the University of Nebraska's Epply Cancer Institute recently reported the first animal evidence that cabbage may help stop the spread of cancer as well as its initial development. For six weeks, the Epply researchers fed some mice regular diets, while others were put on diets high in dried cabbage or collard greens (another cruciferous vegetable). Then they injected the animals with breast cancer cells. Three weeks later, the mice on the diet of cabbage or collard greens had fewer metastasized tumors. "We're encouraged, but we don't know what this might mean to people with cancer," says Dr. Diane Birt, one of the investigators. Citrus: Some experts credit the falling rates of stomach cancer in this country with wide consumption of foods high in vitamin C, including citrus fruits. The vitamin has been shown to block formation of nitrosamines, potent carcinogens. But there may be another way citrus fights cancer. Luke K.T. Lam at the University of Minnesota recently found that nomilin -- a compound that causes bitterness in some citrus juices -- helped block formation of cancerous stomach tumors in mice fed a potent cancer-causing agent. A possible way nomilin works, according to Lam: It triples the activity of an enzyme that helps detoxify poisons in the body, including carcinogens. Milk and cheese: Yes, the same foods that are disparaged by health experts for their heart-damaging high-fat content may possess cancer-fighting potential. In fact, constitutents in dairy fat itself have been labeled anticarcinogens by researcher Michael W. Pariza and colleagues at the University of Wisconsin, Madison. The mysterious anticancer substance, called CLA, is a slightly chemically altered form of linoleic acid, molecules of which form chains to make polyunsaturated fats. Investigators detected high levels of CLA in milk fat and in cheese, especially Cheez Whiz, a processed food to which whey is added. CLA is heavily concentrated in whey, explains Pariza. In test tubes, Pariza contends, CLA is a potent antioxidant that can destroy dangerous "free radicals," rampaging bodily substances that damage healthy cells, helping turn them cancerous. Further, he says, the anticancer CLA becomes incorporated rapidly into cell membranes, which would put CLA on the front lines of defense against cellular assaults by carcinogens. As for the paradox that eating cheese and milk fat may contribute to heart disease, Pariza does not advise megadosing on foods containing CLA. However, this surprising finding gives new rationale for eating some cheese and milk fat as part of a balanced diet, he says. He does not see CLA as a magic-bullet cancer preventive. But he believes it is one of many anticarcinogens in the diet, all of which may work in combination to help fend off cancer. Eating Right appears on alternate Tuesdays.