What Are Polyphenols?

These plant-based foods should be a part of any healthy diet.

You may have heard that some indulgent foods, such as dark chocolate and wine, may actually be good for you. But did you know that one reason behind the benefits of these foods — along with several fruits (e.g., berries, grapes), vegetables (spinach, broccoli), herbs and spices, and drinks (green tea, coffee) — is that they contain high levels of compounds called polyphenols? 

Polyphenols may benefit health in myriad ways, such as by regulating blood sugar, lowering the risk of heart disease, and supporting brain health. But should you add them to your diet? And is it better to get them from polyphenol foods or supplements? Here’s everything you need to know to make smart choices around polyphenols.

What are polyphenols?

Polyphenols are compounds found in plants and which have antioxidant properties. More than 8,000 types have been identified, grouped in four main categories:

  • Flavonoids
  • Phenolic acids
  • Polyphenolic amides
  • Other polyphenols

The type of food, its origin, its ripeness, how it was farmed, how it was transported, and how it was stored can all affect the type and amount of polyphenols found in a food.

What are the best sources of polyphenol foods?

Some of the best sources for polyphenol foods include: 

  • Fruits: berries, currants, grapes, cherries, stone fruits, apples, pears, pomegranates, and some citrus fruits
  • Vegetables: artichokes, carrots, potatoes, onions, spinach, shallots, broccoli, and asparagus
  • Legumes: black beans, soybeans and soy products, and white beans
  • Nuts and seeds: almonds, hazelnuts, pecans, walnuts, and flax seeds
  • Grains: oats, rye, and whole wheat
  • Herbs and spices: basil, marjoram, parsley, peppermint, and spearmint (all dried); cinnamon, cloves, cumin, caraway, rosemary, sage, thyme, and star anise
  • Others: black and green tea, coffee, dark chocolate, red wine, vinegar, ginger, and olives (including olive oil)

What are the best polyphenol supplements?

You can take polyphenols in supplement form, but in general (as of this writing) this is not recommended. Here’s why:

  • Research has not shown that supplements exert the same benefits as foods.
  • Polyphenols work best when combined with other nutrients found in foods.
  • Supplements can interfere with absorption of nutrients such as iron, thiamine, and folate.
  • Supplements are not regulated, and often contain an amount of polyphenols that is much, much higher than what you’d get from foods. No safety studies have been done to determine whether such high levels are safe (or even necessary). In fact, animal studies suggest high-dose supplements can damage the kidneys, alter thyroid function, and may even promote tumor growth.

What are the health benefits of polyphenols?

There are a number of ways polyphenols might help keep you healthy. Generally, they are anti-inflammatory and therefore have the potential to reduce the risk for any disease characterized by increased inflammation. Other, specific ways polyphenols might help support a healthy body include:

  • Supporting healthy digestion: Polyphenols might help support healthy digestion by promoting beneficial bacteria (including probiotics) and fighting off harmful bacteria. The best foods for gut bacteria-friendly polyphenols include green tea (polyphenols in tea) and fermented foods.
  • Supporting brain function: Polyphenol consumption might help boost memory, learning, and concentration as well as increase blood flow to the brain, according to some studies. The best foods for brain-healthy polyphenols include grapes, cocoa, and Ginkgo biloba.
  • Decreased risk of type 2 diabetes: Studies link polyphenol consumption to lower fasting blood sugar, higher glucose tolerance, and increased insulin sensitivity — all of which lower the risk of developing type 2 diabetes. The best foods for diabetes-reducing polyphenols are red, purple, and blue foods (think berries, grapes, etc.).
  • Decreased risk of heart disease: Studies link polyphenols to lower blood pressure and reduced bad cholesterol levels as well as a reduced risk of death from heart disease. The best heart-healthy polyphenol foods include whole grains and flax seeds.
  • Reduced UV-damage to skin: Polyphenols have been shown to protect against UV damage to skin, including a reduced risk of skin cancer. The best polyphenols for skin include green tea, pomegranates, and grape seeds.
  • Prevention of blood clots: Early research shows polyphenols can help block the process of clot formation; however, more studies are needed to confirm these preliminary findings.
  • Protection against cancer: Early research shows that polyphenols can help block the growth and development of cancer cells, and polyphenol consumption has been linked to a lower risk of breast and prostate cancers. However, because other studies show no link, more research is needed.

Polyphenols should be treated as just one part of a healthy diet, however. Many of the foods that contain high levels of polyphenols are also high in fiber, which has its own set of health benefits (including supporting a healthy gut microbiome). Eating a variety of nutritious, whole foods will ensure you get plenty of fiber, polyphenols, and other beneficial compounds. 

Consume certain polyphenol foods in moderation

As with anything, moderation is key when it comes to polyphenols — at least some of them. Foods are complex mixtures of many different compounds, including some that can actually be harmful in large amounts. For example:

  • Although red wine is a great source of polyphenols, drinking too much could prove harmful because of the alcohol it contains. Most studies agree that moderate alcohol intake — e.g., one glass of wine for a woman, two maximum per day for a man  — can be beneficial, but higher quantities negate potential benefits. 
  • Similarly, chocolate should be eaten in moderation due to the sugars typically added during processing. Dark chocolate, which has less sugar and more polyphenols, is the best choice if you do need to satisfy that sweet tooth.
  • Fruits are also a great source of polyphenols, but it’s typically better to eat whole fruits, rather than drink fruit juice. In a whole fruit, the fiber present in the peels and flesh helps control the blood sugar spikes that can occur with the higher concentration of sugar in most juices.

Key takeaways

Polyphenols are antioxidant compounds found in plants. Evidence suggests that they play an important role in supporting health and well-being by promoting healthy gut and brain function and by reducing the risk for diseases such as cancer, type 2 diabetes, and heart disease. Because supplements have been shown to be more harmful than beneficial, the best way to get more polyphenols is to eat a variety of polyphenol foods — such as many vegetables, fruits, nuts and seeds, whole grains, legumes, and certain polyphenol teas. Take care when choosing your sources of polyphenols, and be sure to moderate consumption of any polyphenol foods or drinks that might contain harmful substances such as alcohol or sugar.

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