Polyphenols are a category of chemicals that naturally occur in plants. There are more than 500 unique polyphenols. Collectively, these chemicals are known as phytochemicals.
Polyphenols can be further categorized into the following groups:
- phenolic acids
Read on to learn more about what foods are high in polyphenols, as well as the possible health benefits of consuming them.
Plant-based foods such as vegetables and fruits tend to be high in polyphenols.
The number of polyphenols in a food can vary depending on where the food is grown, how it is farmed and transported, how ripe it is, and how it is cooked or prepared.
See below for some of the most common sources of dietary polyphenols:
|Food group||Some major sources of polyphenols|
|Fruits||oranges, apples, grapes, peaches, grapefruit juice, cherries, blueberries, pomegranate juice, raspberries, cranberries, black elderberries, blackcurrants, plums, blackberries, strawberries, apricots|
|Vegetables||spinach, onions, shallots, potatoes, black and green olives, globe artichoke heads, broccoli, asparagus, carrots|
|Whole grains||whole grain wheat, rye, and oat flours|
|Nuts, seeds, and legumes||roasted soybeans, black beans, white beans, chestnuts, hazelnuts, pecans, almonds, walnuts, flaxseed|
|Beverages||coffee, tea, red wine|
|Fats||dark chocolate, virgin olive oil, sesame seed oil|
|Spices and seasonings||cocoa powder, capers, saffron, dried oregano, dried rosemary, soy sauce, cloves, dried peppermint, star anise, celery seed, dried sage, dried spearmint, dried thyme, dried basil, curry powder, dried ginger, cumin, cinnamon|
Many of the health benefits associated with polyphenols may be related to their role as antioxidants. Antioxidants are known for their ability to combat cell damage.
Polyphenols may also impact genes and gene expression. A person's specific genes can also affect how their body responds to certain types of polyphenols. Polyphenols may even influence gut bacteria.
Type 2 diabetes
According to one review, a type of flavonoid called flavan-3-ols may be especially beneficial for lowering insulin resistance. The same review also found that flavonoids seem to be the type of polyphenol most often associated with a lower risk for type 2 diabetes.
An analysis of studies on flavonoid intake and type 2 diabetes concluded that people who consumed the most flavonoids had a lower risk of developing type 2 diabetes than those who took in the least. Increasing flavonoid intake also appeared to be a way to reduce the risk of disease significantly.
Unprocessed cocoa is a rich source of flavonoids. One review found that cocoa consumption significantly decreased a marker of insulin resistance.
It is worth noting that unprocessed cocoa is very different from the chocolate in candy bars or traditional desserts. Unprocessed cocoa comes straight from the cacao plant with no sugar added.
Rats that received the tea polyphenols were able to keep up their activity for longer than the rats that did not receive the polyphenols. They also had significantly lower levels of chemicals that signaled inflammation and muscle damage in their blood.
Lignans are a class of polyphenols that occur at their highest levels in virgin olive oil, flaxseed, and whole grain rye flour. One way to study lignan intake is to look at levels of lignans in urine.
In a study of adults in the United States, researchers found that higher levels of lignans in the urine were associated with lower levels of measures of inflammation. This could be important since long-term inflammation has been associated with certain diseases, such as heart disease and cancer.
A review of studies looked at the impact of cocoa polyphenols on risk factors for heart disease. Scientists found that consuming cocoa for at least 2 weeks led to a significant decrease in blood pressure.
They also found that cocoa significantly decreased LDL or "bad" cholesterol, and raised HDL or "good" cholesterol.
Polyphenol intake may also play a role in body weight regulation.
One study compared the intake of flavonoids, a class of polyphenols, with body mass index (BMI) and waist circumference. Researchers found that a higher flavonoid intake was associated with lower BMI and waist circumference.
These results are significant because obesity is associated with a higher risk for many chronic diseases
Including foods that are rich in polyphenols as part of a healthful diet is safe for most people. People with food allergies or certain medical conditions may need to avoid certain polyphenol-rich foods, however.
While polyphenols occur naturally in many plant foods, they may be added to some foods, or extracted and used to make supplements.
Even though polyphenols appear to offer many benefits, excessive amounts may have adverse effects. Some supplements contain polyphenols in higher quantities than would be consumed in a healthful diet.
An article on the safety of polyphenols reported that a high dose of one particular polyphenol caused kidney damage in mice. The same article also described several other animal studies in which polyphenols led to tumor development and altered thyroid hormone production.
Some polyphenol-rich foods may also affect the absorption of certain nutrients, as is the case with tea and iron from plant foods. Grapefruit juice is known to interact with multiple medications, and part of this interaction may be related to a type of polyphenol found in grapefruit juice.
Overall, polyphenols appear to offer many promising health benefits. More research is needed before polyphenols can be recommended in supplemental doses, however.
For now, it is best to consume polyphenols in their natural form of plant foods. The Mediterranean diet is one eating pattern that includes many foods that are rich in polyphenols.
As an aside, it is important to note that many studies of polyphenol-rich foods have been sponsored by food companies.