polyphenol
Meaning of polyphenol: A vast family of plant compounds behind bitterness, astringency and some plant colors, and among the most studied parts of the diet.
Definition of polyphenol
A polyphenol is any of a large group of plant compounds built around multiple phenol rings. Thousands are known, and they occur throughout the plant kingdom in fruit, vegetables, tea, coffee, cocoa, olive oil, nuts and whole grains. They contribute bitterness, astringency and in some cases color, and they show strong antioxidant activity in laboratory conditions.
What are the main groups?
| Group | Examples | Common sources |
|---|---|---|
| Flavonoids | Catechins, anthocyanins, quercetin | Tea, berries, onions, cocoa |
| Phenolic acids | Chlorogenic acid | Coffee, fruit |
| Stilbenes | Resveratrol | Grapes, red wine, peanuts |
| Lignans | Secoisolariciresinol | Flaxseed, whole grains |
Only some are pigments. Anthocyanins give the red and purple of berries and red cabbage, but a great many polyphenols are colorless, and tannins are noticed through the drying sensation they produce in the mouth rather than through any color.
Does antioxidant activity in a test tube mean the same in the body?
Not directly, and this is the central caution about the whole group. Measurements of antioxidant capacity are made in a dish, where the compound meets a reactive molecule at a concentration the bloodstream never reaches. Most polyphenols are poorly absorbed, and what is absorbed is chemically altered by the gut wall and liver within hours. Blood levels stay low and fall quickly. Current thinking is that whatever benefits arise come less from mopping up reactive molecules directly and more from effects on cell signaling and on the gut bacteria that break them down.
Why is the research so hard to interpret?
Populations eating more polyphenol-rich foods tend to have lower rates of heart disease, but those foods travel with fiber, potassium, unsaturated fats and different eating patterns overall, so isolating one component is difficult. Trials of concentrated single compounds have generally been less encouraging than the population data. Concentrated supplements also raise a separate issue: at high dose some polyphenols interfere with iron absorption, with thyroid function or with drug-processing enzymes in the liver, effects that do not arise at the amounts present in ordinary food.
Used in a sentence
The analysis compared the polyphenol content of the two beverages.
Good to know
Antioxidant activity measured in the laboratory does not transfer directly to the body, since most polyphenols are poorly absorbed and rapidly altered after being eaten.
Word origin
Where “polyphenol” comes from
Combines the Greek polys, meaning many, with phenol, the chemical ring structure the group is built from.