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).