Polyphenols are a category of plant compounds that offers various health benefits.
Regularly consuming polyphenols is thought to boost digestion and brain health, as well as protect against heart disease, type 2 diabetes, and even certain cancers.
Red wine, dark chocolate, tea, and berries are some of the best-known sources. Yet, many other foods also offer significant amounts of these compounds.
This article reviews everything you need to know about polyphenols, including possible food sources.
What are polyphenols?
Polyphenols are a category of compounds naturally found in plant foods, such as fruits, vegetables, herbs, spices, tea, dark chocolate, and wine.
They can act as antioxidants, meaning they can neutralize harmful free radicals that would otherwise damage your cells and increase your risk of conditions like cancer, diabetes, and heart disease.
Polyphenols are also thought to reduce inflammation, which is thought to be the root cause of many chronic illnesses.
Types of polyphenols
More than 8,000 types of polyphenols have been identified. They can be further categorized into 4 main groups:
- Flavonoids. These account for around 60% of all polyphenols. Examples include quercetin, kaempferol, catechins, and anthocyanins, which are found in foods like apples, onions, dark chocolate, and red cabbage.
- Phenolic acids. This group accounts for around 30% of all polyphenols. Examples include stilbenes and lignans, which are mostly found in fruits, vegetables, whole grains, and seeds.
- Polyphenolic amides. This category includes capsaicinoids in chili peppers and avenanthramides in oats.
- Other polyphenols. This group includes resveratrol in red wine, ellagic acid in berries, curcumin in turmeric, and lignans in flax seeds, sesame seeds, and whole grains.
The amount and type of polyphenols in foods depend on the food, including its origin, ripeness, and how it was farmed, transported, stored, and prepared.
Polyphenol-containing supplements are available as well. However, they’re likely to be less beneficial than polyphenol-rich foods.
Summary: Polyphenols are beneficial plant compounds with antioxidant properties that may help keep you healthy and protect against various diseases. They can be subdivided into flavonoids, phenolic acid, polyphenolic amides, and other polyphenols.
Health benefits of polyphenols
Polyphenols have been linked to various health benefits.
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Polyphenols may lower blood sugar levels
Polyphenols may help lower your blood sugar levels, contributing to a lower risk of type 2 diabetes.
That’s partly because polyphenols may prevent the breakdown of starch into simple sugars, lowering the likelihood of blood sugar spikes after meals.
These compounds may also help stimulate the secretion of insulin, a hormone that’s required to shuttle sugar from your bloodstream into your cells and keep your blood sugar levels stable.
Various studies further link polyphenol-rich diets to lower fasting blood sugar levels, higher glucose tolerance, and increased insulin sensitivity — all important factors in lowering your risk of type 2 diabetes.
In one study, people eating the highest amounts of polyphenol-rich foods had up to a 57% lower risk of developing type 2 diabetes over 2–4 years, compared with those eating the lowest amounts.
Among polyphenols, research suggests that anthocyanins may offer the most potent anti-diabetic effect. They’re typically found in red, purple, and blue foods, such as berries, currants, and grapes.
Polyphenols may lower your risk of heart disease
Adding polyphenols to your diet may improve heart health.
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Experts believe that this is largely due to the antioxidant properties of polyphenols, which help reduce chronic inflammation, a risk factor for heart disease.
Two recent reviews link polyphenol supplements to lower blood pressure and LDL (bad) cholesterol levels, as well as higher HDL (good) cholesterol.
Another review found a 45% lower risk of death from heart disease in those with higher enterolactone levels, which are a marker of lignan intake. Lignans are a type of polyphenol typically found in flax seeds and whole grains.
Polyphenols may prevent blood clots
Polyphenols may reduce your risk of developing a blood clot.
Blood clots are formed when platelets circulating in your bloodstream begin to clump together. This process is known as platelet aggregation and is useful in preventing excess bleeding.
However, excess platelet aggregation can cause blood clots, which can have negative health effects, including deep vein thrombosis, stroke, and pulmonary embolism.
According to test-tube and animal studies, polyphenols may help reduce the platelet aggregation process, thereby preventing the formation of blood clots.
Polyphenols may protect against cancer
Research consistently links diets rich in plant foods to a lower risk of cancer, and many experts believe that polyphenols are partly responsible for this.
Polyphenols have strong antioxidant and anti-inflammatory effects, both of which can be beneficial for cancer prevention.
A recent review of test-tube studies suggests that polyphenols may block the growth and development of various cancer cells.
In humans, some studies link high blood markers of polyphenol intake to a lower risk of breast and prostate cancers, while others find no effects. Therefore, more studies are needed before strong conclusions can be made.
Polyphenols may promote healthy digestion
Polyphenols may benefit digestion by promoting the growth of beneficial gut bacteria while fending off harmful ones.
For instance, evidence suggests that polyphenol-rich tea extracts can promote the growth of beneficial bifidobacteria.
Similarly, green tea polyphenols may help fight off harmful bacteria, including C. difficile, E. Coli, and Salmonella, as well as improve symptoms of peptic ulcer disease (PUD) and inflammatory bowel disease (IBD).
Furthermore, emerging evidence indicates that polyphenols may help probiotics thrive and survive. These are beneficial bacteria that occur in certain fermented foods and can be taken in supplement form. However, more research is needed.
Polyphenols may promote brain function
Polyphenol-rich foods may boost your focus and memory.
One study reports that drinking grape juice, which is naturally rich in polyphenols, helped significantly boost memory in older adults with mild mental impairment in as little as 12 weeks.
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Others suggest that cocoa flavanols may improve blood flow to the brain and have linked these polyphenols to improved working memory and attention.
Similarly, the polyphenol-rich plant extract Ginkgo biloba appears to boost memory, learning, and concentration. It has also been linked to improved brain activity and short-term memory in those with dementia.
Summary: Polyphenols may help prevent blood clots, reduce blood sugar levels, and lower heart disease risk. They may also promote brain function, improve digestion, and offer some protection against cancer, though more research is needed.
Foods rich in polyphenols
Though tea, dark chocolate, red wine, and berries are likely the best-known sources of polyphenols, many other foods also contain high amounts of these beneficial compounds.
Here are the 75 foods richest in polyphenols, listed by category:
- black chokeberries
- black and red currants
- black elderberries
- black grapes
- red chicory
- red lettuce
- red and yellow onions
- black beans
- soybean sprouts
- soy meat
- soy milk
- soy yogurt
- white beans
Nuts and seeds
- flax seeds
- whole wheat
Herbs and spices
- celery seed
- curry powder
- dried basil
- dried marjoram
- dried parsley
- dried peppermint
- dried spearmint
- lemon verbena
- Mexican oregano
- star anise
- black tea
- cocoa powder
- dark chocolate
- green tea
- olives and olive oil
- rapeseed oil
- red wine
Including foods from each of these categories in your diet provides you with a wide variety of polyphenols.
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Summary: Many plant foods are naturally rich in polyphenols. Including a variety of these foods in your diet is a great strategy to boost your intake of these beneficial nutrients.
What about polyphenol supplements?
Supplements have the advantage of offering a consistent dose of polyphenols. However, they also have several potential drawbacks.
First, supplements haven’t been consistently shown to offer the same benefits as polyphenol-rich foods, and they don’t contain any of the additional beneficial plant compounds typically found in whole foods.
Moreover, polyphenols seem to work best when interacting with the many other nutrients naturally found in foods. It’s currently unclear whether isolated polyphenols, such as those in supplements, are as effective as those found in foods.
Finally, polyphenol supplements aren’t regulated, and many contain doses over 100 times larger than those in foods. More research is needed to establish safe and effective dosages, and it’s unclear whether these large doses are beneficial.
Summary: Polyphenol supplements may not offer the same health benefits as polyphenol-rich foods. Effective and safe dosages haven’t been determined.
Potential risks and side effects of polyphenols
Polyphenol-rich foods are safe for most people.
The same cannot be said of supplements, which tend to provide much higher quantities of polyphenols than those typically found in a healthy diet.
Animal studies show that high-dose polyphenol supplements may cause kidney damage, tumors, and an imbalance in thyroid hormone levels. In humans, they may result in an increased risk of stroke and premature death.
Some polyphenol-rich supplements can interact with nutrient absorption or interact with medications. For instance, they may reduce your body’s ability to absorb iron, thiamine, or folate.
If you have a diagnosed nutrient deficiency or are taking medications, it may be best to speak to your healthcare provider about polyphenol supplements before taking them.
In addition, some polyphenol-rich foods, such as beans and peas, may be rich in lectins. When consumed in large quantities, lectins may cause unpleasant digestive symptoms, such as gas, bloating, and indigestion.
If this is an issue for you, try soaking or sprouting your legumes before eating them, as this can help reduce the lectin content by up to 50%.
Summary: Polyphenol-rich foods are considered safe for most people, while supplements may cause more harm than good. To reduce gas, bloating, and indigestion, try soaking or sprouting polyphenol-rich legumes before eating them.
Polyphenols are beneficial compounds in many plant foods that can be grouped into flavonoids, phenolic acid, polyphenolic amides, and other polyphenols.
They may improve digestion, brain function, and blood sugar levels, as well as protect against blood clots, heart disease, and certain cancers.
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More research is needed to identify effective and safe polyphenol supplement dosages.
Therefore, for the time being, it’s best to rely on foods rather than supplements to boost your intake of these healthful compounds.