Vegetables, fruits, pulses (legumes), nuts and seeds are sources of a wide variety of micronutrients and other bioactive compounds. It is not possible to ascribe the association between these foods and lower cancer risk to a causal effect of specific compounds with confidence, as each food contains a complex mixture of different constituents.

Vitamin C (ascorbic acid) is a water soluble vitamin. Humans, like a small number of other animals, cannot synthesize vitamin C, so it is an essential part of diets. Vitamin C is essential for collagen synthesis and also has antioxidant activity. Severe deficiency causes scurvy. It is added to many foods, including bread and soft drinks, in small amounts as an antioxidant preservative. Natural dietary sources are vegetables, tubers, and fruits, including red/yellow (bell) peppers, kiwi fruits, broccoli, papaya, citrus fruits, strawberries, and potatoes, but it is destroyed by heat or contact with the air (when vegetables are chopped) or lost into cooking water.

Vitamin E is a fat-soluble vitamin and a potent antioxidant that occurs as eight different forms: alpha- and gamma-tocopherol are the most common. The most important dietary sources of vitamin E are vegetable oils such as palm, sunflower, corn, soya bean, and olive olis. Nuts, sunflower seeds, and wheat germ are also sources. Wholegrain, fish, peanut butter, green, leafy vegetables, and fortified breakfast cereals also contain this vitamin.

California researchers say taking excessive amounts, or mega doses, of this vitamin C and vitamin E in dietary supplements may actually increase your risk of cancer. "The levels that we found to be optimal for cell growth are the normal levels in the body of people taking normal diets. The ones we found tremendous increase in genetic abnormalities are in the same range as people taking massive oral supplements," by Dr. Eduardo Marban, the director of the Cedars-Sinai Heart Institute. 5 May 2010 (report from cbs5.com, Kim Mulvihill, MD).

Epstein-Barr virus was the first human virus to be directly implicated in cancer development. Most adults are infected with the Epstein-Barr virus, but relatively few will ever develop the cancers of which this virus is a contributory or necessary cause. Other factors beyond infection with the virus are needed to lead to the development of cancer. Environmental factors including some dietary factors are thought to render precancerous epithelial cells sensitive to Epstein-Barr virus infection, which then triggers malignancy.

Epstein-Barr virus is a DNA virus of the herpes family. It is now known that Epstein-Barr virus infects >90% of the worlds adults population. Upon infection, the individual remains a lifelong carrier of the virus. It is transmitted by salivary contact. It primarily infects B lymphocytes (white blood cells that produce antibodies), though it can also infect epithelial cells. Infection usually occurs in childhood and does not usually produce symptoms, but in adults it can cause infectious mononucleosis or glandular fever. It is particularly associated with undifferentiated nasopharyngeal carcinoma, the most prevalent type.

In nasopharyngeal carcinoma, all of the tumor cells carry viral DNA in a monoclonal form. This means that Epstein-Barr virus infection must have occurred quite early in the cancer process, before rapid growth. It is not normally possible to detect Epstein-Barr virus infection in non-cancerous nasopharyngeal cells.

In the broad sense of the word, most meat is processed-cooking is a process. But as commonly used, the term ‘processed meat’ refers to meats (usually red meats) preserved by smoking, curing or salting, or by the addition of preservatives. Meats preserved only by refrigeration, however they are cooked, are usually not classified as ‘processed meat’.

Ham, bacon, pastrami, and salami are processed meats. So are sausages, bratwursts, frankfurters, and ‘hot dogs’ to which nitrites or nitrates or other preservatives are added. Minced meats sometimes fall inside this definition, often if they are preserved chemically, but not always. The same point applies to ‘ham burgers’. Given the importance of this issue, transnational burger caterers should specify the methods they use to process their products.

Nitrite or nitrate is used to preserve processed meats (it is extremely toxic to bacteria) and gives cured meats their recognizable colors and flavors. The addition of nitrite or nitrate to meat is regulated and monitored in most countries. Dietary nitrites and nitrates are probable human carcinogens because they are converted in the body to N-nitroso compounds which are known carcinogens and they have positive association with colon and pancreas cancer.

Plants contain a wide range of biologically active compounds, some of which are known as phytochemicals. There may be as many as 100000 different compounds, which determine particular properties in plants, and in the fruits and vegetables they produce, such as flavor and color. Phytochemicals are classified according to their chemical structure and functional characteristics, and include salicylates, phytosterols, saponins, glucosinolates, polyphenols, protease inhibitors, monoterpenes, phytoestrogens, sulphides, terpenes, and lectins.

It is widely believed that the health benefits of diets high in fruits and vegetables are likely to be due partly to the presence of phytochemicals. For instance, several act as antioxidants, preventing oxidative damage to cells, proteins, and DNA. It is likely that other bioactive phytochemicals have yet to be identified, and those that are known may have additional properties in the body that are not yet understood. But it is thought that nutrients, phytochemicals, and other, as yet unknown, bioactive components act together to influence physiological responses.

Although many phytochemicals are bioactive, they are not essential in the diet and there is no daily requirement, so they are not classed as nutrients. Humans have developed tastes for some phytochemicals, such as the hot flavors of mustard oil, bitter alkaloids, and irritating capsaicins. There is genetically inherited variation in sensitivity to some tastes, for example, the bitter taste of isothiocynates in cruciferous vegetables such as cabbage.

Examples of phytochemicals which can prevent cancer:

• From veggie burgers to milk to protein bars, soy beans are known as a nutrient rich ingredient- there are studies showing soy bean can prevent prostate cancers.
• Pomegranate phytochemical urolithin B suppresses estrogen production and that prevents the proliferation of breast cancer cells and the growth of estrogen-responsive tumors- Cancer Prevention Research, Jan 2010.
• Phytochemicals (vitamins A, C, K, folate, carotenoids and lutein) from leafy veggies and green tea showed lower levels of genetic changes known to give rise to lung cancer in smokers-Cancer Research, Jan 2010.
• Apples contain natural phytochemicals that have a protective effect against liver, breast and colon cancer-Journal of Agricultural and Food Chemistry, Apr 2008.
• Mangos are known to be rich in vitamins C and A, as well as fiber. Polyphenolic compounds in mangos known as gallotannins, a class of natural bioactive compounds believed to help prevent or block the growth of cancer cells-Jan 2010.  http://agnews.tamu.edu/showstory.php?id=1686

Reference: Reports from American Institute for Cancer Research

Freezing and cooling by use of natural ice and snow is a method of food preservation traditionally available only in cold climates or in winter in temperate climates. Natural ice refrigeration on an industrial scale first developed in the late 19^th century, when refrigerated containers used in trains, ships, and then later trucks, greatly increased the production and consumption of red meat. Domestic freezing, chilling, and refrigeration on a mass scale is a phenomenon mostly of the second half of the 20^th century.

Today, much perishable food is solid frozen or chilled. Together with the growth of industrial refrigeration, domestic refrigerators began to be used in the USA, Australia, and New Zealand on the scale in the 1920s, and the Europe and Japan mostly since the 1950s. In Japan, for example, household processing refrigerators increased from 9 per cent in 1960 to 91 per cent in 1970, and 99 per cent in 2004. Supermarkets with freezers, chill cabinets, and domestic refrigerators are now commonable in the cities and towns of tropical countries; poorer rural communities still rely on drying, fermenting, salting, bottling, tinning, and other methods of food preservation, as well as their own gardens and farms. It is unlikely that refrigeration itself has any direct effect on the risk of cancer. Their effects are indirect.

• Refrigeration enables consumption of fresh perishable foods including seasonal vegetables and fruits all year round, as well as of fresh meat.
• Refrigeration reduces microbial and fungal contamination of perishable foods, notably cereals (grains) and pulses (legumes).
• Refrigeration reduces the need for and use of salting, smoking, curing, and pickling as methods of preserving vegetables, fruits and meat.

It can therefore be said that refrigeration (including freezing and chilling) indirectly influences risk of those cancers, the risk of which is affected by the above factors.

Evidence mounting to a judgement of ‘convincing’ or ‘probable’ for such factors relates to cancers of the mouth, pharynx, larynx, masopharynx, oesophagus, lung, stomach, pancreas, liver, and colon.

Reference: Reports from World Cancer Research Fund and American Institute for Cancer Research