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).

Human papilloma viruses (HPVs) infect squamous epithelia and generate warts. They are passed by direct contact; genital HPV infections are sexually transmitted. HPV infection rates are higher in women who have had a higher number of sexual partners (particularly male partners); do not use barrier methods of contraception; and who started having sex at a younger age.

There are more than 100 types of HPV. All can interfere with host-cell machinery that prevents cells from growing and replicating excessively, which are some of the cellular mechanisms that help protect the body against cancer development. Low-risk HPVs cause genital warts; high risk HPVs cause squamous intra-epithelial lesions that can progress to invasive squamous cell carcinoma. The majority of human cervical cancers are associated with high-risk HPV infections. Four subtypes of this virus account for 80 percent of all cervical cancer.

Cervical cancer, which is caused by HPV, is diagnosed in 11,000 women each year in the United States and the disease kills about 4,000 women annually in the USA.  A study led by researchers from Korea University College of Medicine in Seoul, Korea in the year 2010 suggests that dietary supplements may be taken to reduce risk of cervical cancer (Ref). To be specific, the study found that taking vitamin supplements reduced risk of cervical intraepithelial neoplasia or cervical dysplasia, which has a small chance of becoming cervical cancer. Cervical intraepithelial neoplasia is caused by chronic infection of the cervix with the sexually transmitted HPVs.

HPV infection tends to remain dormant, and with repeated infection, the HPV genome becomes integrated within the host cell genome and some cells may become cancerous.

Most HPV infections do not become persistent, and most persistent HPV infections do not lead to cancer. However, HPV infection is demonstrably present in 99 percent of women with cervical cancer, and may be present but undetected in the remainder. HPV is a necessary while not sufficient cause of cervical cancer.

There is some limited evidence that eating vegetables and fruits can protect against persistence (Ref). There is also evidence that folate can reduce persistence and independently reduce the risk of precancerous lesions in high-risk HPV infected women (Ref).

FDA and EU approved Gardisil for men to prevent genital warts resulting from HPV. GlaxoSmithKline has developed a vaccine called Cervarix for cervical cancer which has been approved some places and is in approval process elsewhere.

Constant mechanical irritation of epithelial surfaces causes inflammation, which predisposes to the development of cancer. It has also been suggested that foods and drinks with chemically irritant components may be a cause of cancers of those sites with which they come into direct contact. Again there is not much evidence for this theory, with the possible exception of chilli and stomach of cancer.

There is, however, some evidence that some thermally hot drinks are a cause of cancers of those sites with which they come into direct contact. The mate (cimarron), an herbal infusion is probably a cause of cancer of the esophagus, and there is limited evidence suggesting that it is also a cause of other cancers of the oral cavity. It is because of the way the infusion is traditionally drunk in the pampas region within the southern cone of Latin America, in northern Argentina, Paraguay, and southern Brazil. It is drunk extremely hot from a gourd through a metal straw, which is often kept rested in the mouth, rather like the stem of tobacco pipe. There is also limited evidence suggesting that various other very hot drinks and foods are a cause of cancer of the esophagus when they are consumed regularly.

Some studies are looking into whether barbecued, fried and roasted meat cooked at high temperatures can increase the risk. These methods of cooking increase the content of chemicals called heterocyclic amines in food and these chemicals may increase cancer risk. (Ref).

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.