PHYTOCHEMICALS

Plants manufacture chemicals, known as phytochemicals, that have multiple functions. Some attract insects to encourage fertilization while others provide defenses against predators such as viruses and animals. Phytochemicals exhibit diversified physiologic and pharmacologic effects. Active derivatives extracted from leaves, stems, roots, flowers and fruits of plants may be classified into three main categories. The first are compounds such as pyrrolizidine alkaloids, nicotine and hydrazine derivatives that are highly toxic and have no discernible therapeutic use. The second are morphine, digitalis and vinca alkaloids. These may be toxic but can elicit useful physiologic responses for treatment of disease when used in controlled amounts or for defined clinical conditions. The third group may exhibit chemopreventive activity against diseases such as atherosclerosis, cancer and diverticular disease. Most active are high molecular weight fibers (celluloids, pectins, lignins) and low molecular weight compounds (carotenoids, dithiolthiones, flavanoids, indole carbinols, isothiocyanates, mono- and triterpenoids, and thioallyl derivatives).

Deficiencies: The majority of phytochemicals that have chemopreventive activity have no clearly defined role as essential nutrients except for the vitamins (ascorbate, tocopherols). Although phytochemical deficiencies have not been identified, their low concentrations in the diet have been associated with increased risks for cancer, cardiovascular diseases, and diabetes.

Diet recommendations: Epidemiological, laboratory, and clinical data substantiate inclusion of increased quantities of fruits and vegetables in the diet. The precise quantity of each plant or its constituents that may prevent or alter disease progression is under investigation; therefore, recommendations cannot be made at this time. The National Cancer Institute suggests an increase of dietary fiber from grains, fruits and vegetables from the current intake of 12 g to 15-20 g/day.

Food sources: All plants are sources of high molecular weight fibers. Specific low molecular weight phytochemicals with chemopreventive activity are contained within a variety of plants. Cruciferous plants, such as cabbage and broccoli, are excellent sources of indoles, dithiolthiones, isothiocyanates and chlorophyllins. Legumes (soybeans, peanuts, beans and peas) contain flavanoids, isoflavanoids and other polyphenols that act as antioxidants and estrogenic agonists/antagonists. Citrus fruits and licorice root contain mono- and triterpenes that act as antioxidants, cholesterol synthesis inhibitors, and stifle growth of rapidly dividing cells. Thioallyl derivatives are found in garlic, leeks and onion, and prevent thrombi formation, decrease cholesterol synthesis, and prevent DNA damage.

Toxicity: Most phytochemicals are non-nutritive substances that can be beneficial and/or physiologically or pharmacologically active. Depending on the quantities consumed, duration of consumption, and the conditions of use, most phytochemicals have the potential capacity to produce cellular or tissue injury.

Recent research: Clinical and laboratory studies currently focus on cardiovascular protection and anticarcinogenic effects of phytochemicals. Risk factors of cardiovascular disease may be ameliorated by lowering cholesterol formation, blocking platelet aggregation, and/or altering prostaglandin formation. Anticancer activities include enhancing detoxification enzymes and antioxidant capacity, inhibition of DNA adduct formation, altering hormone metabolism, and modifying promotion and mechanisms of progression.

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