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What are Polyphenols? Health Benefits for Heart and Gut Health

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What are Polyphenols? Health Benefits for Heart and...

You know that certain foods, like berries or green tea, are good for you. But what’s the secret behind their health benefits? Polyphenols. These important plant chemicals are strong antioxidants that defend against oxidative stress and can play a key role in preventing a wide range of chronic diseases. (1) Polyphenols also boost the production of the body’s antioxidants, including glutathione, catalase, and superoxide dismutase. (2)

person cutting up vegetables on a wooden board in kitchen

Brightly colored fruits and vegetables are among the best sources of antioxidant-rich polyphenols.

What are polyphenols?

Polyphenols aren’t a single nutrient. Instead, “polyphenol” is an umbrella term that covers several types of protective phytochemicals, including:


Flavonoids are pigmented antioxidants found in many brightly colored fruits and vegetables, and they are the most widely consumed type of polyphenol in the human diet. The flavonoid family includes anthocyanidins, which are found in red, purple, and blue foods like blueberries, pomegranates, and purple grapes; flavonols like quercetin and kaempferol, which are found in cruciferous vegetables, alliums, and beans; flavanols found in cocoa, red wine, and green or white tea; and the isoflavones in legumes. (3)

Phenolic acids

These are bioactive polyphenols with antioxidant, antimicrobial, and anti-inflammatory properties. They make up about 30 percent of the polyphenols we eat and can be found in nuts, fruits like berries and grapes, red wine, and coffee. (4)


Although stilbenes aren’t as prevalent in the diet as flavonoids and phenolic acids, they include two well-known antioxidants: resveratrol and pterostilbene. Preliminary studies suggest that stilbenes may help prevent age-related diseases due to their ability to defend against oxidative stress. (5)

Did you know?
Polyphenols are also known by the tongue-twisting moniker polyhydroxyphenols.

4 health benefits of polyphenols

Because of their powerful antioxidant and anti-inflammatory property, polyphenols may protect against the damage caused by oxidation and inflammation. As such, a diet rich in polyphenols may lower the risk of a wide range of degenerative and chronic diseases. (6) Here are the 4 most well-documented health perks provided by polyphenols:

dark chocolate flakes in a bowl and chocolate bars

Dark chocolate is a heart-healthy source of flavonoids that can improve multiple cardiovascular risk factors.

1. Polyphenols lower the risk of cardiovascular disease

It’s no secret that a diet rich in fruits and vegetables can support heart health. Numerous studies have linked the higher polyphenol content in these foods to a variety of cardiovascular benefits. For instance, the polyphenols in pomegranate juice reduce oxidative stress and help keep platelets from clumping together. They also inhibit LDL cholesterol oxidation—a key factor in the development of atherosclerosis. (7)

The flavonoids in cocoa have also been found to reduce multiple cardiovascular risk factors. A study review published in The Journal of Nutrition reported that cocoa consumption reduced systolic blood pressure and LDL cholesterol while boosting HDL cholesterol. Cocoa also improved flow-mediated dilation, which enhanced blood flow through the arteries. (8) Another review found that people who ate a diet high in polyphenols had a markedly lower risk of dying from cardiovascular disease compared to those eating fewer polyphenol-rich foods. (9)

2. Boost cognition

Oxidative damage contributes to neurological conditions like Alzheimer’s disease and dementia. A diet high in polyphenol-rich foods may enhance brain power and protect against age-related cognitive decline. Several studies have found a variety of polyphenols—including resveratrol from grapes, epigallocatechin-3-gallate from green tea, curcumin from turmeric, and quercetin from onions—can protect against toxins that affect the brain, reduce inflammation, and may promote better memory and cognition. (10)(11) One study found that drinking grape juice—which is a rich source of resveratrol—resulted in significantly better memory in older adults with mild cognitive impairment in as little as 12 weeks. (12)

3. Reduce the risk of diabetes

Polyphenols have been shown to support healthy blood sugar levels and may help reduce the risk of type 2 diabetes. Australian research reports that polyphenols prevent the breakdown of dietary starches into simple sugars that can rapidly raise blood sugar. (13)

Polyphenols also support pancreatic function, reduce inflammation and oxidative stress, and inhibit the formation of advanced glycation end products. (14) A study that appeared in the British Journal of Nutrition found that a higher polyphenol intake was directly linked to a lower rate of type 2 diabetes among a group of adults in Eastern Europe. The researchers noted that, while phenolic acids and stilbenes contributed to this association, the real stars were flavonoids. (15)

cut and jug of green tea on a table

Green tea may improve the microbiota and help to reduce the symptoms of inflammatory gastrointestinal conditions.

4. Improve gut health

Digestion is also positively impacted by polyphenols. Studies suggest that, in the gut, polyphenols act like prebiotics. This fosters the growth of beneficial bacteria like Lactobacillus and Bifidobacteria strains. (16)(17) They also appear to stimulate gastrointestinal immunity, reduce inflammation, and inhibit harmful bacteria. (18) A joint study review by researchers at the University of Louisville, Kentucky, and Ohio State University found that the polyphenols in green tea reduced inflammation in the large intestine and improved the symptoms of both inflammatory bowel disease and peptic ulcer. They also found that the polyphenols in carob powder helped shorten symptoms in a group of children with acute diarrhea. (19)

Polyphenols in food

Dozens of foods are packed with polyphenols, making it easy to get a daily dose of powerful antioxidants. These nutritional superstars can be found in a range of plant based foods, including:

  • Fruits: Apricots, apples, berries, black currants, cherries, grapes, grapefruit, oranges, peaches, plums, pomegranates
  • Vegetables: Asparagus, broccoli, carrots, chicory, globe artichokes, olives, onions, potatoes, spinach
  • Grains: Oats, rye, wheat
  • Beans and legumes: Black beans, soybeans, white beans
  • Nuts and seeds: Almonds, chestnuts, flaxseed, hazelnuts, pecans, walnuts
  • Fats: Dark chocolate, olive oil, sesame seed oil
  • Beverages: Coffee, tea, red wine
  • Herbs and spices: Capers, celery seed, cinnamon, cloves, cumin, curry powder, dried herbs like basil, ginger, peppermint, oregano, rosemary, sage, thyme

Did you know?
Satisfying that chocolate craving with a treat containing cocoa powder can deliver a healthy dose of flavanols. But adding milk or fat may negate the health benefits those flavanols provide.

Polyphenol supplements

For people whose diets are lacking in fresh fruits and vegetables, supplements may seem like an easy way to get your polyphenols. Popular polyphenol supplements shown to cause health benefits include:

  • Epigallocatechin-3-gallate (EGCG)
  • French grape seed extract
  • Pycnogenol
  • Quercetin
  • Resveratrol

For instance, EGCG supplements have been shown to lower cholesterol levels in postmenopausal women. (20) Supplemental grape seed extract has been found to support healthy blood pressure. (21) And a recent study review concluded that resveratrol supplementation effectively increased antioxidant levels and reduced inflammatory markers in people with metabolic syndrome. (22) But, as beneficial as supplements can be, they may have a downside.

Did you know?
Supplements may provide important polyphenols to those who don’t eat many fruits or vegetables, but high doses should be taken with caution.

Polyphenol supplements: safety considerations

Some people assume that because polyphenols come from natural sources, they are safe and free from side effects, but this may not always be true. Research in the American Journal of Clinical Nutrition notes that some polyphenols can adversely interact with certain medications. (23) One well-known example is quercetin (which is found in grapefruit juice). This polyphenol can interact with blood-thinning medications like warfarin and increase the risk of bleeding.

Another study in the American Journal of Clinical Nutrition reports that high-dose polyphenol supplements may have carcinogenic and estrogenic effects, and may increase the risk of thyroid issues. (24) Since most of these potential problems appear to be dose-dependent, work with your practitioner to determine the best dose to meet your individual needs.

The bottom line

Flavonoids, phenolic acids, and stilbenes possess a treasure trove of health benefits. But, when it comes to boosting your polyphenol levels, think food first. If you do opt to take a supplement, mind the dose and remember more is not always better!

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  1. Williamson G. The role of polyphenols in modern nutrition. Nutr Bull. 2017;42:226-35.
  2. Tsao R. Chemistry and biochemistry of dietary polyphenols. Nutrients. 2010;2:131-46.
  3. Szalay J. What are flavonoids? Live Science. 2015. Available at:
  4. Saibabu V, Fatima Z, Khan LA, et al. Therapeutic potential of dietary phenolic acids. Adv Pharmacol Sci. 2015;Article ID 823539, 10 pages.
  5. Reinisalo M, Karlund A Koskela A, et al. Polyphenol stilbenes: Molecular mechanisms of defence against oxidative stress and aging-related diseases. Oxid Med Cell Longev. 2015;2015:340520.
  6. Pandey KB, Rizvi SI. Plant polyphenols as dietary antioxidants in human health and disease. Oxid Med Cell Longev. 2009;2(5):270-8.
  7. Aviram M, Domfeld L, Rosenblat M, et al. Pomegranate juice consumption reduces oxidative stress, atherogenic modifications to LDL, and platelet aggregation: Studies in humans and in atherosclerotic apolipoprotein E-deficient mice. Am J Clin Nutr. 2000;71(5):1062-76.
  8. Shrime MG, Bauer SR, McDonald AC, et al. Flavonoid-rich cocoa consumption affects multiple cardiovascular risk factors in a meta-analysis of short-term studies. J Nutr. 2011;141(11):1982-8.
  9. Kim Y, Je Y. Flavonoid intake and mortality from cardiovascular disease and all causes: A meta-analysis of prospective cohort studies. Clin Nutr ESPEN. 2017;20:68-77.
  10. Spangnuolo C, Napolitano M, Tedesco I, et al. Neuroprotective role of natural polyphenols. Curr Top Med Chem. 2016;16(17):1943-50.
  11. Daglia M, Di Lorenzo A, Nabavi SF, et al. Polyphenols: well beyond the antioxidant capacity: gallic acid and related compounds as neuroprotective agents: you are what you eat! Curr Pharm Biotechnol. 2014;15(4):362-72.
  12. Krikorian R, Nash TA, Shidler MD, et al. Concord grape juice supplementation improves memory function in older adults with mile cognitive impairment. Br J Nutr. 2010;103(5):730-4.
  13. Kim Y, Keogh JB, Clifton PM. Polyphenols and glycemic control. Nutrients. 2016;8:17.
  14. Xiao JB, Högger P. Dietary polyphenols and type 2 diabetes: current insights and future perspectives. Curr Med Chem. 2015;22(1):23-38.
  15. Grosso G, Stepaniak U, Micek A, et al. Dietary polyphenols and risk of type 2 diabetes in the Polish arm of the Health, Alcohol and Psychosocial factors in Eastern Europe (HAPIEE) study. Br J Nutr. 2017;118(1):60-8.
  16. Lee HC, Jenner AM, Low CS, et al. Effect of tea phenolics and their aromatic fecal bacterial metabolites on intestinal microbiota. Res Microbiol. 2006;157(9):876-84.
  17. Pacheco-Ordaz R, Wall-Medrano A, Goñi MG, et al. Effect of polyphenol compounds on the growth of selected probiotic and pathogenic bacteria. Lett Appl Microbiol. 2018;66(1):25-31.
  18. Laparra JM, Sanz Y. Interactions of gut microbiota with functional food components and nutraceuticals. Pharmacol Res. 2010;61(3):219-25.
  19. Dryden GW, Song M, McClain C. Polyphenols and gastrointestinal diseases. Curr Opin Gastroenterol. 2006;22(2):165-70.
  20. Samavat H, Newman AR, Wang R, et al. Effects of green tea catechin extract on serum lipids in postmenopausal women: a randomized, placebo-controlled clinical trial. Am J Clin Nutr. 2016;104(6):1671-82.
  21. Kim JK, Kim KA, Choi HM, et al. Grape seed extract supplementation attenuates the blood pressure response to exercise in prehypertensive men. J Med Food. 2018;21(5):445-53.
  22. Tabrizi R, Tamtaji OR, Lankarani KB, et al. The effects of resveratrol supplementation on biomarkers of inflammation and oxidative stress among patients with metabolic syndrome and related disorders: a systematic review and meta-analysis of randomized controlled trials. Food Funct. 2018;9(12):6116-28.
  23. Martin KR, Appel CL. Polyphenols as dietary supplements: A double-edge sword. Nutr Diet Supp. 2009;2010(2):1-12.
  24. Mennen LI, Walker R, Benntau-Pelissero C, et al. Risks and safety of polyphenol consumption. Am J Clin Nutr. 2005;81(suppl):326S-9S.


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