What Are Polyphenols?

Polyphenols are a group of compounds that are largely beneficial to health. They’re naturally found in plants and plant-based foods like fruits, vegetables, herbs, tea, red wine, coffee, and dark chocolate. 

Polyphenols help protect the body and neutralize free radicals that cause damage to cells. Free radicals are highly reactive oxygen molecules produced by normal cell processes. External factors like radiation, air pollution, smoking, and chemical exposure can also create free radicals.

Since they help protect from free radicals, polyphenols are considered antioxidants. Without antioxidants to neutralize free radicals, the body’s cells get injured, which increases your risk of health problems like diabetes, heart disease, and cancer.

Keep reading to learn more about the types of polyphenols, their possible health benefits, and their potential risks.

Types of Polyphenols

Over 8,000 polyphenols have been discovered but researchers are still trying to understand how the chemicals affect the human body.

Flavonoids

Flavonoids make up over half of the currently known polyphenols. The five different types of flavonoids are:

• Anthocyanins
• Flavan-3-ols
• Flavones
• Flavanones
• Flavonols

Flavonoids are found in foods like onions, kale, parsley, tea, red wine, and soybeans. 

Phenolic Acid

Phenolic acid accounts for about 30% of all known polyphenols. The two classes of phenolic acid are hydroxybenzoic acid and hydroxycinnamic acid. Phenolic acid is found in foods like grapes, berries, pomegranates, walnuts, chocolate, coffee, and green tea.

Polyphenolic Amides

Polyphenolic amides have subgroups called capsaicinoids and avenanthramides. Capsaicinoids are found in chili peppers and create the hotness of the pepper. Avenanthramides are found in oats and are believed to help with LDL (low-density lipoprotein or “bad”) cholesterol. 

Other Polyphenols

Some polyphenols only have one type, and they account for a smaller portion of the compounds. This group includes polyphenols like:

• Resveratrol is unique to grapes and red wine.
• Ellagic acid is found in berry fruits, such as strawberries and raspberries, and the skin of tree nuts.
• Curcumin is a strong antioxidant that gives the spice turmeric its yellow color.
• Lignans are found in flax, sesame, and some other grains.

Health Benefits of Polyphenols

Most of the health benefits of polyphenols relate to their role as an antioxidant. Antioxidants help protect cells from damage caused by free radicals. It’s thought that eating enough antioxidants may help keep your body’s cells healthy and lower your risk for some diseases.

Researchers are still discovering the health benefits of polyphenols, so more research is needed to understand all the benefits this compound could provide. Here are the potential health benefits of polyphenols.

Lower Blood Sugar Levels 

Polyphenols may help keep blood sugar levels within a healthy range. One study suggested that regularly consuming tea was associated with a lower risk of developing type 2 diabetes. 

Summaries of medical studies (systematic reviews) and examinations of data from many independent studies (meta-analyses) have suggested that each cup of coffee consumed daily may reduce a person’s risk of developing diabetes by up to 8%.

The anthocyanins found in berries and grapes are another polyphenol associated with lowering the risk of developing and helping to manage type 2 diabetes. 

It’s believed that these polyphenols help blood sugar levels by:

• Protecting the insulin-producing cells in the pancreas from oxidation by free radicals
• Reducing inflammation
• Preventing starches and simple carbs from being fully digested, which helps prevent blood sugar spikes

Increase Insulin Sensitivity

One of the potential causes of type 2 diabetes is insulin resistance. When you become insulin resistant, your body’s cells become less responsive to the hormone insulin. As a result, glucose stays in the bloodstream longer. 

Increasing the cells’ sensitivity to insulin helps bring more glucose in from the blood and keep blood sugar levels within a healthy range. 

One clinical trial looked at the effects of adding more than 300 milligrams of polyphenols from strawberries and cranberries to participants’ diets. The researchers found that the polyphenols in strawberries and cranberries effectively increased insulin sensitivity in people with insulin resistance. 

Lower Cancer Risk

Plant-based diets are frequently linked to a lower cancer risk and polyphenols are thought to contribute to that reduced risk.

Research has shown that polyphenols may reduce the risk of developing some types of cancer, such as:

• Colon cancer
• Prostate cancer
• Skin (epithelial) cancer
• Endometrial (lining of the uterus) cancer
• Breast cancer

Since antioxidants help prevent cell damage, it’s believed polyphenols may lower the chances of cells mutating from damage and becoming cancerous. Polyphenols like flavonoids may help control tumor cell growth and signal cell death to remove cancerous cells (apoptotic factors).

Reduce Inflammation

Chronic inflammation is linked to an increased risk of developing many health conditions, like heart disease, diabetes, cancer, and autoimmune diseases.

One study looked at the effect of polyphenol lignans on inflammatory markers in the body. The study found the higher the concentration of lignans in the body, the lower a person’s markers of inflammation were.  

Improve Heart Health

Adding more polyphenols to your diet may improve your heart health and lower your risk of cardiovascular diseases. Polyphenols may improve multiple risk factors for heart disease, including:

• Lower blood pressure
• Lower LDL ("bad) cholesterol
• Raise HDL ("good") cholesterol
• May prevent blood clots

Resveratrol, lignans, and flavonoids have all been linked to lower heart disease risk. However, it is worth noting that not all studies have shown these benefits. For example, resveratrol has not always been shown to have heart-health benefits, but it could be because red wine is usually consumed in smaller amounts than other antioxidant-rich foods and drinks since it contains alcohol.

Boost Brain Function

Some studies have suggested that polyphenols may boost brain function and protect against neurodegenerative diseases like Alzheimer’s disease. 

For example, some research suggests that curcumin, a powerful polyphenol found in turmeric, can have an effect on neurodegenerative (brain) diseases like Alzheimer’s. However, more study is needed.

Another study found that older adults who drank green tea were less likely to experience cognitive decline than people who drank coffee or black tea.

The benefits for brain function could be related to the antioxidant effects and improvements in blood flow to the brain.  

Improve Digestion

Polyphenols may improve your digestion by promoting the growth of beneficial bacteria in your GI tract while limiting the growth of harmful ones.

For example, studies have suggested that blueberries may promote the growth of the “good” bacterium bifidobacteria. Green tea may slow the growth of potentially harmful bacteria like Clostridioides difficile (C. diff), Escherichia coli (E. coli), and Salmonella typhimurium.

The microbiome is the balance of microbes normally present in the digestive tract. Researchers are just starting to understand the gut microbiome’s role in overall health. It’s believed the bacteria in the gut play a role in mental health, the immune system, digestion, and more. So, maintaining a healthy balance of good bacteria is thought to support your overall health. 

Polyphenol-Rich Foods

Polyphenols are found in a variety of plant-based foods. Usually, people have heard of the antioxidants in popular foods like dark chocolate, tea, red wine, coffee, and berries. You may not know polyphenols are also in many other common foods, including:

Vegetables

Vegetables high in polyphenols include:

• Broccoli
• Carrots
• Spinach
• Red lettuce
• Onions
• Asparagus
• Artichokes
• Shallots
• Garlic

Fruits

Fruits high in polyphenols include:

• Blueberries
• Strawberries
• Raspberries
• Blackberries
• Cranberries
• Grapes
• Cherries
• Lemon
• Grapefruit
• Oranges
• Pears
• Apples
• Peaches
• Plums
• Pomegranate
• Nectarine
• Apricots
• Olives and olive oil

Grains

Grains high in polyphenols include:

• Oats
• Rye
• Wheat

Nuts and Seeds

Nuts and seeds high in polyphenols include:

• Walnuts
• Almonds
• Flaxseed
• Chia seeds
• Pecans
• Chestnuts
• Hazelnuts

Legumes

Legumes high in polyphenols include:

• Black beans
• White beans
• Soybeans
• Tofu
• Tempeh (made from fermented soybeans)
  

Herbs and Spices

Herbs and spices high in polyphenols include:

• Turmeric
• Cinnamon
• Cumin
• Cloves
• Celery seed
• Basil
• Ginger
• Marjoram
• Parsley
• Peppermint
• Oregano
• Rosemary
• Sage
• Thyme
• Lemon verbena

Other

Other foods and drinks high in polyphenols include:

• Green tea
• Black tea
• Red wine
• Dark chocolate
• Cocoa powder
• Coffee
• Vinegar

Risks and Side Effects

Eating a balance of polyphenol-rich foods is safe for most people. 

However, if you’re considering trying a polyphenol supplement, understand that there could be potential side effects. Supplements are not regulated by the Food and Drug Administration (FDA) and they tend to deliver higher doses of polyphenols than what you would get from food.

More research is needed to understand the safety and effectiveness of polyphenol supplements. Be sure to talk with your healthcare provider before taking any new supplements. 

Many polyphenol-rich foods are high in other compounds, like fiber. Suddenly increasing your fiber intake can lead to some digestive discomfort, like gas, bloating, and constipation. If you’re looking to increase the number of polyphenols in your diet, try adding more slowly.

Lectin is another component of plant-based foods. Some food sources that are high in these proteins are raw legumes and whole grains. Given lectins' ability to bind to other foods, research suggests that they could disrupt digestion, weaken the intestines, and cause nutrient deficiencies. 

If you eat foods with large amounts of lectin and notice you have symptoms, try soaking and cooking foods with lectins (such as dried beans and other legumes) before eating because doing so can decrease the lectin content by up to 50%.

Summary

Polyphenols are compounds naturally found in plant-based foods. They act as antioxidants and may help lower your risk for certain diseases. Examples of polyphenols include flavonoids, phenolic acid, polyphenolic amides, resveratrol, curcumin, and lignans.

The potential health benefits of polyphenols include a lower risk of heart disease, diabetes, cancer, inflammation, and cognitive decline. Foods that are rich in polyphenols include berries, beans, oats, garlic, spinach, and other plant-based foods. 

While you can also get polyphenols from supplements, know that they are not regulated by the FDA. Make sure to talk to your provider before trying one.