Cancer develops over a long time, which means that you have years——typically decades——in which to hinder or promote it. Researchers are finding that what you eat may interfere with cancer growth at various stages. For example, certain foods can block the chemicals that initate cancer. Antioxidants(抗氧化剂), found in some vitamins and minerals, can snuff out oxygen free radicls (氧自由基), substances that are thought to make cells more susceptible to cancer, and they can even repair some of the cellular damage that has been done. And some food—wheat bran(麦,糠) in particular—has been shown to shrink precancerous(癌症前期的) cells. A recent review of 17 studies from 17 nations reveals that people who eat the most fruits and vegetables have about half the cancer raters of those who eat the least. In fact, some research suggests that frequent consumption of fruits and vegetables can cut the risk of lung cancer even in smokers. One of the most studied antioxidants in vegetables and fruits thought to protect against cancer is beta-carotene(β胡萝卜素), concentrated in deep green, yellow and orange vegetables such as carrots, sweet potatoes and spinach. Research also shows that beta-carotene can change in the body to retinoic acid (维生素A酸), a substance used in clinical trials to treat certain cancers. Here are some of the foods that contain cancer-fighting chemicals. Tomatoes. One of the compounds in tomatoes that is thought to reduce the risk of cancer is lycopene(蕃茄素), the pigment (色素) that makes tomatoes red. Lycopene, an antioxidant that is also found in watermelons and apricots, quenches certain cancer-triggering oxygen free fadicals. Healthy people with the most blood lycopene. Green Vegetables. A recent Italian study showed that dark-green leafy vegetables lower the risk of many cancer. Spinach, broccoli, kale and dark-green lettuces are chock-full of antioxidants, including beta-carotene, folate(叶酸) and lutein(叶黄素).A good rule of thumb(单凭经验的做法) : the darker the vegetable, the more antioxidants within. Pungent preventives(刺激性的预防物). A whole host of chemicals thought to have cancer-inhibiting properties have been identified in allium vegetables, which include garlic, onions and scallions(大葱). Animal studies show that many of these chemicals block carcinogens that have been linked to colon, stomach, lung and liver cancer. A study at Pennsylvania State University found that feeding rats various garlic extracts and preparations(配制好的食物) reduced mammary tumors by as much as 71 percent. In humans, studies suggest that those who eat more onions and garlic are less prone to gastrointestinal cancer. Research suggests that garlic compounds may even interfere with cancer progression. A recent German study found that ajoene, a garlic compound, is toxic to malignant cells. Garlic may also antagonize existing cancer by boosting(促进) immune functions, according to researchers at Loma Linda University School of Medicine. Their study, done on mice, found that garlic's sulfur compounds increased the activity of macrophages and T-lymphocytes(淋巴细胞), two of the components of the immune system that destroy tumor ceils. Recent research indicated that what people eat may help to significantly reduce their risk of developing cancer.