Superfood is a term sometimes used to describe food with high phytonutrient content that may confer health benefits as a result. For example, blueberries are often considered a superfood (or superfruit) because they contain significant amounts of antioxidants, anthocyanins, vitamin C, manganese, and dietary fiber. However, the term is not in common currency amongst dieticians and nutritional scientists, many of whom dispute the claims made that consuming particular foodstuffs can have a health benefit.
There is no legal definition of the term and it has been alleged that this has led to it being over-used as a marketing tool.
Phytochemicals are chemical compounds such as beta-carotene that occur naturally in plants. The term is generally used to refer to those chemicals that may affect health. While there is growing evidence to support the health benefits of diets rich in fruits and vegetables, there is only limited evidence to suggest these effects are due to specific phytochemicals.
Phytochemicals as candidate therapeutics
Phytochemicals have been used as drugs for millennia. For example, Hippocrates may have prescribed willow tree leaves to abate fever. Salicin, having anti-inflammatory and pain-relieving properties, was originally extracted from the white willow tree and later synthetically produced to become the staple over-the-counter drug called Aspirin. There is evidence from laboratory studies that phytochemicals in fruits and vegetables may reduce the risk of cancer, possibly due to dietary fibers, polyphenol antioxidants and anti-inflammatory effects. Specific phytochemicals, such as fermentable dietary fibers, are allowed limited health claims by the US Food and Drug Administration (FDA).
An important cancer drug, Taxol (paclitaxel), is a phytochemical initially extracted and purified from the Pacific yew tree.
Among edible plants with health promoting phytochemicals, diindolylmethane, from Brassica vegetables (broccoli, cauliflower, cabbage, kale, Brussels sprouts) may be useful for recurring respiratory papillomatosis tumors (caused by the human papilloma virus), is in Phase III clinical trials for cervical dysplasia (a precancerous condition caused by the human papilloma virus) and is in clinical trials sponsored by the National Cancer Institute of the United States for a variety of cancers (breast, prostate, lung, colon, and cervical).
The compound is being studied for anti-viral, anti-bacterial and anti-cancer properties through a variety of pathways and has been shown to synergize with Taxol in its anti-cancer properties, making it a possible anti-cancer phytochemical as taxol resistance is a major problem for cancer patients.
Some phytochemicals with physiological properties may be elements rather than complex organic molecules. Abundant in many fruits and vegetables, selenium, for example, is involved with major metabolic pathways, including thyroid hormone metabolism and immune function. Particularly, it is an essential nutrient and cofactor for the enzymatic synthesis of glutathione, an endogenous antioxidant.
Clinical trials and health claim status
There are currently many phytochemicals possibly having medicinal properties in clinical trials for a variety of diseases. Lycopene, for example, from tomatoes has been tested in clinical trials for cardiovascular diseases and prostate cancer. These studies, however, did not attain sufficient scientific agreement to conclude an effect on any disease.
The FDA position reads:
"Very limited and preliminary scientific research suggests that eating one-half to one cup of tomatoes and/or tomato sauce a week may reduce the risk of prostate cancer. The United States Food and Drug Administration concludes that there is little scientific evidence supporting this claim."
Likewise, although lutein and zeaxanthin may affect visual performance and inhibit macular degeneration and cataracts, there was insufficient scientific evidence from clinical trials for such a specific effect or health claim.
Food processing and phytochemicals
Phytochemicals in freshly harvested plant foods may be destroyed or removed by modern processing techniques, possibly including cooking. For this reason, industrially processed foods likely contain fewer phytochemicals and may thus be less beneficial than unprocessed foods. Absence or deficiency of phytochemicals in processed foods may contribute to increased risk of preventable diseases.
Interestingly, a converse example may exist in which lycopene, a phytochemical present in tomatoes, is either unchanged in content or made more concentrated by processing to juice or paste, maintaining good levels for bioavailability.
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