There is strong evidence that certain foods (including those with a high fibre content, fruit, vegetables, soya products and some teas) can help to protect against cancer, while others (such as smoked and charred meats and saturated fats) contain carcinogens (cancer-forming agents) and therefore actually encourage the disease. Most cancer experts believe that around one-third of all cancers could be prevented by healthy changes to the diet. Although the protective merits and harmful effects of certain foods are gaining acceptance by the medical profession, the role of diet in the actual treatment of cancer remains contentious.
Cancer occurs when living cells start to behave in a disorderly fashion. Cancer cells are normal body cells whose DNA (the structure that stores a person’s genetic inheritance and is present in every body cell) has become distorted or lacks essential information. These changes, or mutations, in DNA happen spontaneously, occurring more often on exposure to oxidants, such as tobacco smoke in the case of lung cancer. Cancer cells grow and divide without any restraint and start to compete with the body’s normal cells. The cancer cells then go on to invade other parts of the body, causing destruction of tissues.
The foods that are currently regarded as the most powerful in preventing cancer are fruit and vegetables. The World Cancer Research Fund reviewed more than 4000 human diet studies from around the world and concluded that, by increasing the amount of fruit and vegetables in the diet and reducing consumption of alcohol and meat, an individual can reduce the risk of developing a broad range of cancers by 30-40 per cent. The World Health Organization recommends that people eat a minimum of five servings of fruit and vegetables each day, and that they also try to include some nuts, seeds and pulses in their daily diet. Fresh produce is best, but if this is unavailable, then frozen or canned produce may be substituted.
The beneficial effect of fruit and vegetables is due to a group of active and protective compounds known as phytonutrients. Phytonutrients are found in fruit and vegetables, and include the vitamins and minerals known as antioxidants which are known to help counteract the effect of harmful free radicals.
Free radicals are potentially dangerous by-products of the body’s normal chemical processes. Exposure to radiation and pollution, as well as certain foods, can increase their production. An imbalance of free radicals in the body encourages conditions that allow the development of some cancers.
To benefit from a broad range of phytonutrients, it is important to eat a good variety of fruit and vegetables. The principal antioxidants are: betacarotene (which is turned into vitamin A by the body), contained in orange and yellow produce such as carrots, apricots, mangoes, pumpkin and sweet potatoes, and in tomatoes and spinach; vitamin C, contained in citrus fruits, strawberries, melons, kiwi fruit and blackcurrants; vitamin E, contained in green leafy vegetables, vegetable oils, nuts and wheat-germ; and the mineral selenium, which is best obtained from a supplement.
Cruciferous vegetables such as Brussels sprouts, broccoli, cabbage, cauliflower, spinach and kale contain phytonutrients called indoles that can help to protect against breast cancer. Tomatoes, red grapefruit and sweet red peppers are all a good source of lycopene, a close relative of betacarotenc. Members of the allium vegetable family (onions, leeks, garlic and chives) contain sulphur compounds that help the body to neutralize carcinogens.
A group of phytonutrients known as phyto-oestrogens, thought to help in the prevention of breast cancer, are contained in soya beans and soya products such as tofu, soya sauce and soya milk. The phyto-oestrogens are thought to mimic the female hormone oestrogen, which promotes breast and cervical cancer. The body may therefore be tricked into making less oestrogen, thereby lowering the risk of cancer. Scientists believe that the protective effect of eating diets high in soya protein may partly explain the low rates of breast cancer observed in China and Japan. Diets rich in soya protein are also usually low in saturated fat and animal protein.
It has been found that green and black teas contain substances called polyphenols (catechins) that have cancer-preventing properties. These substances act in the same ways as anti-I oxidants, neutralizing cell-damaging free radicals. Ordinary tea bags often contain inferior grades of black tea, so it is worth seeking out good quality teas at health food stores and speciality tea shops. Green tea (made from the unfermented leaf of the Camellia sinensis tea plant) contains more polyphenols than black tea.
Foods that are high in dietary fibre can help to protect against cancer of the colon, rectum, prostate, uterus and breast; all these cancers are associated with a typical Western high-fat, low-fibre diet. Fibre in the diet decreases the time between eating and the elimination of waste material from the body, thus reducing time that dietary carcinogens come into contact with the intestines. Good sources of fibre include fruit, vegetables, pulses, wholegrain cereals and products made from them such as wholemeal bread and pasta.
Vegetarians may be less likely to contract cancer of the colon than meat eaters, because their diet is typically low in saturated fat and high in fibre. Vegans are at even less risk, because they exclude all animal products from the diet. In addition, because fruit and vegetables often form the mainstay of a vegetarian diet, vegetarians are likely to consume more phyto-nutrients than meat eaters. Many vegetarians eat tofu as a source of protein, and therefore benefit from the phyto-oestrogens contained in soya products.