Phytochemicals are sometimes referred to as phytonutrients; these terms are often used interchangeably. In broad terms, they are said to be any chemical or nutrient derived from a plant source. However, in common usage, they have a more limited definition. They are usually used to refer to compounds found in plants that are not required for normal functioning of the body but that nonetheless have a beneficial effect on health or an active role in the amelioration of disease. Thus, they differ from what are traditionally termed nutrients in that they are not a necessity for normal metabolism, and their absence will not result in a deficiency disease -- at least not on the timescale normally attributed to such phenomena. A minority claim that many of the diseases afflicting the people of industrialized nations are the result of those people's lack of phytonutrients in their diet. What is beyond dispute is that phytonutrients have many and various salubrious functions in the body. For example, they may promote the function of the immune system, act directly against bacteria and viruses, reduce inflammation, and be associated with the treatment and/or prevention of cancer, cardiovascular disease and any other malady affecting the health or well-being of an individual.
Many phytochemicals are antioxidants that impart bright colors to fruits and vegetables. Lutein makes corn yellow, lycopene makes tomatoes red, carotene makes carrots orange and anthocyanin makes blueberries blue, for example. Both the bright colors and the antioxidant activities are due to alternating single-bonded and double-bonded carbons. There is abundant evidence from epidemiological studies that the phytochemicals in fruits and vegetables can significantly reduce the risk of cancer, probably due to antioxidant and anti-inflammatory effects. But studies of supplementation with large doses of beta-carotene in smokers have shown an increase in cancer risk (possibly because excessive beta-carotene results in breakdown products that reduce plasma Vitamin A and worsen the lung cell proliferation induced by smoke).
Phytochemicals naturally occur in vegetables and fruit and highest levels are therefore consumed by vegetarians and vegans.
Families of phytochemicals
The following are groups or families of related phytochemicals and
common sources of phytochemicals arranged by family.
Food processing and phytochemicals
Many phytochemicals are thought to be destroyed or removed by modern food processing techniques, possibly including cooking. For this reason, it is believed that industrially processed foods are less beneficial (contain fewer phytochemicals) than unprocessed foods. The absence or deficiency of phytochemicals is believed to have contributed to the increased prevalence of the above-cited preventable or treatable causes of death in contemporary society. Interestingly though, lycopene, which is a phytonutrient that can be found in tomatoes, is concentrated in processed foods such as spaghetti sauce and ketchup, making those foods much better sources of lycopene than fresh tomatoes.