Polyphenols are a group of naturally-occurring, bioactive compounds, with great potential to benefit your health. They are obtained through diet, through a variety of commonly consumed foods.
This article covers what polyphenols are, what they do, benefits, risks, and the best sources of polyphenols.
What Are Polyphenols?
Polyphenols are biologically active micronutrients (aka phytochemicals or phytonutrients) found in most plants.
In the plant, their purpose is to carry out functions like UV protection, pathogen defense, and protection from predators. They also give brightly coloured plants (like fruits and veggies) their pigmentation.
When we humans eat plant foods, we acquire the polyphenols which can have many different effects on the human body. (more detail on health effects coming up).
We get polyphenols through many commonly consumed foods such as fruits, vegetables, grains, coffee, tea, and spices.
Types of polyphenols
There are thousands of different types of polyphenols. Some of the major classes of polyphenols are flavonoids, phenolic acids, lignans, stilbenes, polyphenolic amides, and phenolic alcohols.
The most common polyphenols are flavanoids – most of the polyphenols we get from our diets are flavonoids.
There are many types of flavonoids, with the major subclasses being flavones, flavonols, flavanols, flavanones, isoflavones, and anthocyanins.
Different foods contain different amounts of the various types of polyphenols. And different types of polyphenols can affect the body differently.
Health Benefits of Polyphenols
Here are some of the ways that polyphenols can benefit human health:
1. Reduce cellular damage
One major beneficial function of polyphenols is their antioxidant activity.
Your body produces something called free radicals as a result of normal cellular metabolism. Things like aging and stress can also contribute to free radical formation. Free radicals are highly reactive molecules which can be harmful to the body if not regulated.
Antioxidants are the molecules that neutralize these free radicals in the body, thereby reducing oxidative stress and damage.
Polyphenols act as powerful antioxidants and work to reduce oxidation and inflammation in the body. Most of the antioxidants we get from our diet, are polyphenols.
In addition to antioxidant activity, polyphenols also have anti-inflammatory properties and can help reduce the chronic, systemic inflammation that is associated with many chronic diseases.
By reducing cellular and genetic damage (caused by oxidative and inflammatory stress), polyphenols have the potential to reduce the risk of chronic diseases such as cancer and neurodegenerative diseases, as well as the deterioration that occurs with aging.
Some studies suggest that the antioxidant and anti-inflammatory properties of polyphenols may help reduce risk of cancer (1).
Clinical trials are limited, but majority of laboratory studies have shown that polyphenols display anti-cancer properties such as disrupting the production of cancer cells, blocking tumor growth, and inducing cancer cell death (1).
More studies, especially human clinical trials, are needed to assess the effects of dietary polyphenol consumption on cancer risk, and the exact mechanisms of their anti-cancer properties.
Similarly, some polyphenols may have neuroprotective effects against neurodegenerative diseases like Alzheimer’s and Parkinson’s, but clinical study is limited (2).
2. Promote cardiovascular health
Polyphenols, especially flavonoids, may help reduce risk of cardiovascular disease by keeping blood pressure in check, maintaining blood vessels integrity, and reduce chronic inflammation.
Meta-analyses of randomized controlled trials have found that cocoa flavanols significantly improve markers of cardiometabolic disease, such as lipid metabolism, insulin resistance, hypertension, and systemic inflammation (3, 4).
Additionally studies have shown that consumption of flavanol-rich foods such as chocolate and tea, are associated with reduced risk of stroke and heart attack (5, 6, 7). Similarly, anthocyanin consumption has been linked to reduced risk of heart attack in men and women (8, 9).
An observational study of over 7000 participants found that greater intake of polyphenols, especially flavanols, lignans, and hydroxybenzoic acids, was associated with decreased risk of cardiovascular disease (10).
Similarly, a large prospective study of over 90,000 participants found that flavonoid consumption was associated with a lower risk of death from cardiovascular disease (11).
However, it is important to note that clinical trials are still needed to confirm any cardioprotective effects of polyphenols and establish appropriate dietary recommendations.
3. Reduce risk of diabetes
In addition to reducing risk of cardiovascular disease, polyphenols may also help reduce risk of type 2 diabetes by managing blood sugar and insulin levels, and reducing insulin resistance.
Lab and animal studies have suggested that dietary polyphenols display anti-diabetic action by reducing blood glucose, improving vascular function, and stimulating insulin secretion (12).
Human clinical trials are limited, but some studies have shown that consumption of polyphenol-rich foods have anti-diabetic effects in individuals with, or at risk of, type 2 diabetes.
One randomized controlled trial reported that a polyphenol-rich diet reduced blood glucose response, increased early insulin secretion, and improved insulin sensitivity in individuals at high cardiometabolic risk (these individuals had a high waist circumference and at least one other symptom of metabolic syndrome) (13).
In terms of specific polyphenols, studies have found that some individual polyphenols such as resveratrol and anthocyanins may improve blood sugar management (aka glycemic control) and insulin secretion/sensitivity in individuals with insulin resistance (14).
Overall, polyphenol consumption is likely beneficial to individuals at risk of insulin resistance and diabetes, and may have implications for diabetes and blood sugar management.
4. Promote gut health
Polyphenols may also help keep your gut microbiome healthy by feeding beneficial bacteria and limiting harmful bacteria.
Several studies have shown that polyphenols have the ability to alter the gut microbiome, positively affect beneficial gut bacteria, and hence benefit your overall gut health.
Some polyphenols, especially the polyphenols found in green and black tea (such as EGCG and other catechins), can inhibit the growth of many potentially harmful bacteria and viruses, such as H.pylori, S. aureus, E. coli, Salmonella, Listeria, Hep C virus, influenza virus, HIV, Epstein-Barr virus, and Candida fungi (15). Similar inhibition of H. pylori was also demonstrated by citrus polyphenols (16).
What’s more, polyphenols may promote growth of beneficial gut bacteria, while inhibiting harmful species (17, 18).
A healthy, balanced gut microbiome plays a major role in maintaining a healthy immune system, as well as almost all other systems and functions of the body.
Risks of Polyphenols
Polyphenol-rich foods include a variety of commonly consumed foods that are generally considered healthy.
In fact, it is thought that most foods that benefit your health are mostly beneficial because of the polyphenols they contain.
Think fruits, vegetables, and other whole foods – it is usually recommended to include these foods in your diet and they are generally safe to consume regularly.
However, polyphenol supplements can contain much larger amounts of polyphenols than those found in natural whole food sources.
For this reason, there may be risks or side-effects associated with taking polyphenol supplements. High doses of polyphenols may interact with hormones, nutrients and other bioactive molecules in the body.
Research suggests that high polyphenol consumption can interfere with (non-heme) iron absorption, interact with pharmaceutical agents, and may even have carcinogenic effects (19).
Further scientific research is still needed to determine what amounts of polyphenol consumption are optimal and safe.
The takeaway may be to stick with a healthy and balanced, whole-food diet. There are plenty of ways to get polyphenols through diet, without needing supplementation…
15 Foods High in Polyphenols
All amounts are in mg of polyphenols per 100g or 100mL, and come from this study.
1. Olives & olive oil
- black olives: 569 mg
- green olives: 346 mg
- extra virgin olive oil: 62 mg
2. Berries
Contain high amounts of flavonoids called anthocyanins, which give brightly coloured red/purple/blue plants their pigmentation. Berries with the highest amounts of polyphenols include:
- black chokeberries: 1756 mg
- black elderberries: 1359 mg
- blueberries: 560 – 836 mg
- blackcurrants: 758 mg
- blackberries: 260 mg
- strawberries: 235 mg
- raspberries: 215 mg
3. Other fruits
Some other fruits high in polyphenols include:
- plums: 377 mg
- cherries: 274 mg
- prunes: 194 mg
- grapes: 169 mg
- apples: 136 mg
- peaches: 59 mg
4. Fruit Juices
- pure apple juice: 68 mg
- pure pomegranate juice: 66 mg
- pure blood orange juice: 56 mg
- pure grapefruit juice: 53 mg
- pure lemon juice: 42 mg
5. Vegetables
Many vegetables are good sources of polyphenols. Some of the vegetables with the highest amounts include:
- artichokes: 260 mg
- chicory: 235 mg (red), 166 mg (green)
- onions: 168 mg (red), 74 mg (yellow)
- shallots: 113 mg
- spinach: 119 mg
- broccoli: 45 mg
6. Nuts
Most nuts contain polyphenols. Nuts with the highest amounts include:
- chestnuts: 1215 mg
- hazelnuts: 495 mg
- pecans: 493 mg
- almonds: 187 mg
7. Flaxseeds
- flaxseed meal: 1528 mg
8. Cocoa powder
Cocoa is made from cacao seeds which contain flavanols. Raw cocoa has the largest amount of flavanols. The flavanol content decreases as the cocoa or chocolate becomes more refined.
- cocoa powder: 3448 mg
- dark chocolate: 1664 mg
- milk chocolate: 236 mg
9. Coffee
- filtered coffee: 214 mg
10. Tea
Both black and green tea contain plenty of polyphenols, especially the catechin epigallocatechin gallate (EGCG) which is the most abundant catechin in tea.
- black tea: 102 mg
- green tea: 89 mg
11. Red wine
Just like grapes, red wine contains resveratrol. Rosé and white wine also have polyphenols, but not as much as red wine.
- red wine: 101 mg
- white wine: 10 mg
- rosé wine: 10 mg
12. Spices
Many spices are some of the richest sources of polyphenols, especially:
- cloves: 15,188 mg
- peppermint (dried): 11,960 mg
- star anise: 5460 mg
- oregano (dried): 2319 mg
- sage: 1207 mg
- rosemary: 1018 mg
- thyme: 878 mg (dried), 163 mg (fresh)
- basil (dried): 322 mg
13. Legumes
Polyphenol-rich legumes include:
- soybeans: 246 mg
- black beans: 59 mg
- white beans: 51 mg
14. Soy
In addition to soybeans, polyphenols can be found in other forms of soy such as:
- soy flour: 466 mg
- tempeh: 148 mg
- soy yogurt: 84 mg
- tofu: 42 mg
15. Grains
Dietary polyphenols can be found in whole grains such as:
- whole wheat (whole grain hard wheat flour: 201 mg)
- rye (whole grain rye flour: 143 mg)
- oats (whole grain oat flour: 37 mg)
Summary
Polyphenols are bioactive micronutrients obtained though plant foods. They have various health benefits including promoting gut health and reducing harmful oxidation, inflammation, cellular damage, risk of heart disease, diabetes, cancer, and more. There may be some risks associated with polyphenol consumption, especially from supplements, such as interference of iron absorption. Polyphenols can be obtained through a range of healthy, dietary sources, such as fruits, vegetables, cocoa, coffee, tea, nuts, legumes, and more.
That’s it for this article on polyphenols and foods high in polyphenols! If you liked this article or have any questions, feel free to leave a comment!