English: Fruit stall in Mysore, Karnataka. Apples, pomegranates and citrus fruits are stacked into neat pyramids and towers. (Photo credit: Wikipedia)
Polyphenols, which comprise the major group of antioxidants consumed by humans in food, are a large family of plant chemicals. Several hundred of these chemicals have been found in plants and they are believed to protect the plants from disease and irradiation damage. Polyphenols are antiviral, antibacterial, antiinflammatory and anticarcinogenic in humans.
Flavonoids comprise the largest group of polyphenols. The following is an outline of polyphenols:
I. Flavonoids.
a. Flavonols.
b. Flavones.
c. Isoflavones.
d. Flavanones.
e. Anthocyanidins.
f. Flavanols.
1. Catechins.
2. Proanthocyanidins.
II. Stilbenes.
a. Resveratrol.
lII. Hydroxybenzoic acids.
IV. Hydroxycinnamic acids.
V. Lignans.
VI. Tannins.
The polyphenols that we consume, as much as 1 gram of polyphenols daily, are concentrated in the stomach and the rest of the gastrointestinal (GI) tract but are not well absorbed into the rest of the body. High therapeutic levels are achieved within the GI tract as a result of the poor absorption into the blood.
Polyphenols give plants and fruits flavor and color. Flavanols tend to appear in the skin and leaves of plants and are frequently found in brewed and fermented drinks since they are in the leaves. Examples include green tea (Camellia sinensis) catechins, quercetin and kaempferol in wine, quercetin in onions and apples, myricetin in berries and flavones and flavonones in citrus fruits. Flavanols and flavones are not usually found together. Polyphenols are found in vegetables, cereal grains, chocolate and dried legumes.
Polyphenols act against oxidative stress diseases (such as cancer and inflammatory diseases), cardiovascular diseases and neurological diseases (such as Alzheimer’s). Polyphenols have been shown to have antioxidant activity, improve cell survival, increase the destruction of abnormal cells (apoptosis) and prevent the growth of tumors. They prevent inflammatory and tumor-promoting cycloxygenase and lipoxygenase activity.
Polyphenol activity in the body is altered by the way plants are harvested, processed and metabolized after eating. Polyphenols in the blood are coupled with other chemicals (conjugated) and unfortunately, they work best when they are unconjugated. Because of these factors, polyphenols are being studied at this time for their benefits in gastrointestinal and liver disease.
Large amounts of unabsorbed polyphenols reach the colon where they are metabolized by colonic flora and increase the growth of colonic bacteria. Polyphenols are of benefit in many diseases that come from the lining cells of the intestine, including Crohn’s disease (inflammatory bowel disease), peptic ulcer disease and cancer. Green tea relieves inflammatory bowel disease, and green tea extract (GTE) reduces inflammation and increases protection from oxidation.
A polyphenol extract from apples reduces diarrhea from cholera toxin. A carob pod powder, rich in tannins, improved acute diarrhea in pediatric patients.
Helicobacter pylori (H. pylori) is a kind of bacteria found in the digestive tract which promotes peptic ulcers, gastritis and gastric cancer. Treatment with high doses of green tea catechins reduced this inflammation and increased beneficial apoptosis.
Colorectal cancers are the second leading cause of cancer deaths. Epidemiologic studies show the protective benefits of high polyphenol diets. A study of tea drinking Chinese people showed the likely protective effect of green tea from colon and pancreatic cancer. (Low fat diets were protective, also.)
Silymarin, a flavanoid concentrate of milk thistle (Silybum marianum), protects the liver from inflammation and is safely used in toxic hepatitis, viral hepatitis, fatty liver and alcoholic cirrhosis. Silymarin protects the liver in Amanita muscarina mushroom poisoning.
GTEs are protective in liver disease and in rats GTE prevented liver transplant failure and liver fibrosis.
CONCLUSION: Polyphenols are of benefit in diseases of the gastrointestinal tract, liver and pancreas. The beneficial doses are not known because of the absence of clinical studies in humans. The best studied are polyphenols from green tea, green tea extracts, milk thistle and silymarin extracts. Benefit has been shown in inflammatory disease, H. pylori and colorectal cancer.
NOTE: Matcha is a form of green tea that is especially high in polyphenols. Matcha powder is made from the whole leaf of green tea. This is in contrast to the hot water extract of tea leaves that is usually consumed. Polyphenols do not extract well in hot water and much of the beneficial effect is thrown out with the tea bag or used leaves.
Read about cancer prevention by polyphenols.
To read the author’s abstract of the article click on the link to the author’s title above.
PMID: 16462174.
Summary #148.
