Phytochemicals are naturally occurring chemical compounds in plants. Phyto means "plant" in Greek. They are responsible for a plant's organoleptic properties, such as the deep purple of blueberries, or the smell of garlic. Some phytochemicals have been considered as possible drugs for millennia, while others, like carotenoids, are significant as provitamin compounds. However, with the exception of dietary fiber, phytochemicals are not established as essential nutrients. There may be as many as 4,000 different compounds in plants that are regarded as phytochemicals with potential for biological activity.
Phytochemicals as medicines and nutrients
Without specific knowledge of their cellular actions or mechanisms, phytochemicals have been considered possible drugs for millennia. For example, salicin, having anti-inflammatory and pain-relieving properties, was originally extracted from the bark of the white willow tree and later synthetically produced to become the common, over-the-counter drug, aspirin.
The biological or nutritional effects of most phytochemicals are unknown. The carotenoids, beta-carotene, alpha-carotene, and beta-cryptoxanthin, however, are well-established as provitamin A compounds essential for normal growth and development, immune system function, and vision. Other carotenoid phytochemicals, such as lycopene, lutein and zeaxanthin, are not yet fully understood for their possible nutritional or biological effects.
Considerable research has been conducted on the possible properties of phytochemicals like polyphenols, but there is insufficient evidence to date that they have any effect from dietary intake or use as dietary supplements.
There is only limited scientific evidence that phytochemicals have biological activity or nutritional value. Nondigestible dietary fibers from plant foods, often considered as a phytochemical, are now generally regarded as a nutrient group having approved health claims for reducing the risk of some types of cancer and coronary heart disease.
According to the American Cancer Society, "no evidence has shown that phytochemicals taken as supplements are as good for your long-term health as the vegetables, fruits, beans, and grains from which they are extracted."
Effects of food processing
A converse exists in the case of carotenoids, such as lycopene present in tomatoes, which may remain stable or increase in content from cooking due to liberation from cellular membranes in the cooked food. Food processing techniques like mechanical processing can also free carotenoids and other phytochemicals from the food matrix, increasing dietary intake.
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