Dietary Polyphenols: What Are They? What Are The Foods Rich In Them?

What attracts you to a plate of food before you taste it? Appearance and color, isn’t it? Bright and colorful vegetables or fruits contain substances called polyphenols that give them the color. This group of biomolecules are more than just pigments.

Polyphenols are found in plants and act as shields against several health issues, including cancer. How do you get them? From where do you get them? What do they do for your body ?We’ve got all the answers! It’s a long ride, so get set and scroll ahead!

Table Of Contents

• What Are Polyphenols? Why Are They Important For Your Body?
• What Are The Types Of Polyphenols? How Are They Classified?
• Top Dietary Sources Of Polyphenols
• How Are Polyphenols Beneficial To Your Body?
• In What Ways Could Polyphenols Be Harmful To Your Body?

What Are Polyphenols? Why Are They Important For Your Body?

Polyphenols are a class in micronutrients. They are plant-based non-nutrients that have bioactive properties. Polyphenols are characterized by bitterness, astringent odor, and color. To date, more than 8,000 phenolic compounds have been identified in plants.

In plants, these bioactive compounds have key functions – providing antioxidant effects, protecting from UV light, and preventing and neutralizing pest attacks.

In humans, polyphenols mediate various complex biochemical processes, resulting in disease prevention, cleaning up toxins, improved nutrient absorption and assimilation, etc. (1).

Any idea what biochemicals fall under the umbrella of polyphenols? Here’s a list!

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What Are The Types Of Polyphenols? How Are They Classified?

Compounds like flavonoids, tannins, and phenolic acids, along with their various chemically modified or polymerized derivatives, fall under polyphenols (1).

Polyphenols are divided into four different categories based on their chemical structure (2):

1. Flavonoids

• Predominantly found in fruits, green tea, legumes, red wine, and vegetables.
• Further divided into subgroups namely, anthocyanidins, catechins, chalcones, flavones, flavonols, flavanones, and isoflavones. They are involved in free radical scavenging and inflammatory reactions.

2. Stilbenes

• Present in grapes, peanuts, and red wine.
• Resveratrol is the most well-known compound among the group.

3. Lignans

Found in algae, cereals, flax seeds, fruits, grains, linseed, legumes, etc.

4. Phenolic Acids

• Divided into two subgroups, namely, hydroxybenzoic acids and hydroxycinnamic acids.
• Abundant in apples, blueberries, cherries, cinnamon, coffee, kiwis, plums, and tea.

As discussed earlier, these polyphenols have a multitude of benefits, including anticancer, anti-inflammatory, antidiabetic, osteoprotective, and cardioprotective properties. This means that polyphenols can be extremely helpful when added to your diet. But what foods contain polyphenols in abundance? Scroll down and start noting your favorites!

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Top Dietary Sources Of Polyphenols

1. Vegetables And Fruits

Vegetables and fruits are the staple components of at least one meal across cuisines in the world. They are the natural sources of a variety of polyphenols – like hydroxybenzoic acid, gallic acid, caffeic acid, coumaric acid, anthocyanins, quercetin, kaempferol, luteolin, apigenin, and epicatechin (3).

Check out the list of commonly eaten fruits and veggies to understand better (3):

2. Spices And Herbs

Spices and herbs not only add flavor to your food, but they are also treasure troves of polyphenols. Raw spices like cinnamon, cloves, fennel, ginger, parsley, rosemary, sage, and thyme contain a considerable amount of these bioactive ingredients.

Simmering, microwaving, and stewing them increases their antioxidant potential as the heat releases the polyphenols. On the other hand, dry heating, frying, and grilling decreases their antioxidant capacity (4).

Herbs and spices can enhance the production of free radical scavengers like superoxide dismutase. They can also control chronic inflammation and related conditions.

The following table lists a few commonly used herbs and spices (4):

3. Nuts And Legumes

In legumes, lentils (Lens culinaris) are natural sources of flavonols and phenolic acids. They have high levels of luteolin, naringenin, anthocyanins, gallic acid, hydroxycinnamic acid, hydroxycoumarins, and proanthocyanidins. These polyphenols have neuroprotective, anticancer, antidiabetic, hypotensive, cardioprotective, and hypolipidemic properties (5).

Similarly, nuts have abundant polyphenols. Several tree nut varieties, including walnuts, pistachios, cashews, hazelnuts, etc., have a varying composition of flavonoids, flavones, proanthocyanidins, and resveratrol. Nuts also contain lignans that possess phytoestrogenic activity (6).

4. Beverages

Tea, coffee, and cocoa are some of the highest producers of polyphenols in a diet. These polyphenols are generated during fermentation and roasting. Not all polyphenols are equally bioavailable in these drinks, which is why they have different benefits.

Almost one-third of the orally consumed polyphenols are transferred into your bloodstream. Hence, when taken in moderation, beverages are one of the effective natural sources of polyphenols (7).

Chlorogenic acids and other active ingredients in coffee can reduce the risk of type 2 diabetes, several types of cancers, cardiovascular diseases, Alzheimer’s, and Parkinson’s disease. Tea is rich in catechins that have similar properties (7).

Red wine, dark chocolate, and high-flavonoid cocoa are also rich in polyphenols – particularly flavonoids. These are potent antioxidant and anti-inflammatory agents. Hence, such beverages can protect your body and increase life expectancy (7).

Take a look at this table, for a quick recap.

Quite an extensive list, right? You now know why fruits, veggies, beverages, nuts, and oils are a staple in our diets.

But, let me remind you – moderation is key. When you pick your favorite polyphenol booster(s), look at the polyphenolic content and frame a dose accordingly.

The policy you could follow is ‘5-in-a-day.’ You can eat 5 portions of fruit or vegetable per day to get your quota of polyphenols. Due to their unknown and complex mechanisms, it is difficult to narrow down to a fixed dose of polyphenols to be taken per day (8), (1).

Alright! Let’s presume you do the 5-in-a-day policy or whatever your doctor suggested. What would be the benefits of doing so? Ever thought about it?

If yes, you’re on the right track. And if you haven’t thought of it yet, we’ve got your back!

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How Are Polyphenols Beneficial To Your Body?

1. Help Fight Cancer

Polyphenols, such as curcumin, anthocyanins, epigallocatechin gallate (EGCG), and resveratrol, are known for their anticancer activity. They help in the modulation of molecular events and signaling pathways associated with cell survival (9).

They interfere in the proliferation, differentiation, migration, and angiogenesis of cancerous cells, Polyphenols induce apoptosis (cell death), work on the immune responses, and reduce tumor burden in the body (9).

However, some of them have shown to pose adverse effects on hormone-related cancers. Hence, their use should be limited and done with utmost caution and medical regulation (9).

2. Control Weight Gain And Obesity

Catechins, resveratrol, anthocyanins, curcumin, and related polyphenols alter physiological and genetic pathways involved in metabolism, energy production, and adiposity (10).

Polyphenols present in the above-listed ingredients might suppress fat absorption, inhibit adipogenesis (cell differentiation) and lipogenesis (formation of fat), promote lipolytic pathways/processes, kill mature adipocytes, and prevent lipid peroxidation and related inflammatory responses (11).

However, there is a need for further extensive research that supports this benefit.

3. Prevent And Treat Cardiovascular Diseases

Along with antioxidant properties, polyphenols may have immunomodulatory and vasodilatory effects. These may contribute to reducing the risk of cardiovascular diseases. The class of polyphenols primarily involved in protecting your heart is flavonoids.

Flavonols, flavanones, flavan-3-ols, flavones, anthocyanins, and isoflavones are widely distributed in berries, beverages, chocolate, citrus fruits, and red and purple vegetables.

Lignans are another class of polyphenols present in flax seeds and sesame seeds. Resveratrol is a well-studied stilbene that has anti-inflammatory effects.

Collectively, polyphenols suppress pro-inflammatory activities at a molecular level, increase the availability of nitric oxide (which gets depleted due to inflammation), maintain blood pressure, modify the immune system cell-signaling cascade, and improve endothelial structure and function (12).

4. Control Inflammation And Related Diseases

Chronic inflammation in our body leads to type 2 diabetes, atherosclerosis, osteoporosis, neurodegenerative disorders, and GERD.

Polyphenols, such as apigenin, catechin, epigallocatechin gallate, luteoloside, quercetin, rutin, tangeretin, morin, and hesperetin, can help treat inflammatory diseases (13).

These polyphenols scavenge free radicals and control cellular activities in pro-inflammatory cells. They also inhibit the activity of enzymes like COX-2 that are associated with inflammation.

Research shows that drinking three cups of tea per day reduces the risk of cardiovascular diseases by 11% (13).

Cacao is another high-flavonoid food that can help in this context (14).

Consuming high-polyphenol beverages daily can reduce the risk of onset of dementia, aging, and neurodegenerative diseases like Alzheimer’s and Parkinson’s (13).

Increasing the fruit intake can prevent age-related bone loss and depletion of bone mineral density (15).

5. Promote Digestion And Healthy Gut

Due to their anti-inflammatory properties, polyphenols can treat GERD, ulcers, diarrhea, and other gut-associated inflammatory diseases effectively.

Green tea extracts, particularly, exhibited antibacterial activity. Green tea is known to keep your gut free from bacterial invasions and lipopolysaccharide-induced inflammation (16).

Many antidiarrheals in traditional medicine were to have polyphenols as their bioactive ingredients.

Their potent antioxidant activity enables polyphenols to protect the GI tract from various types of cancers. They may orchestrate the destruction of cancerous cells and support the survival of healthy cells, eventually preventing the tumors from growing and metastasizing (16).

These molecules can inhibit various biochemical pathways, but they are poorly absorbed from the gut. This is why their concentration is higher in the gut (luminal fluid) than in the serum (16).

Could that mean trouble?

Well, yes. The unaltered polyphenols act directly on the intestinal cells and microflora. This might disrupt the way we digest and assimilate certain nutrients. In other words, it is all about balance.

Scroll down to understand how polyphenols can be harmful.

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In What Ways Could Polyphenols Be Harmful To Your Body?

• Carcinogenic Effects – May be attributed to isoflavones, which can interfere with thyroid hormone biosynthesis and estrogen activity. This may create an imbalance, leading to detrimental effects (17).
• Iron Deficiency – Some polyphenols inhibit the absorption of non-heme iron (iron from plant sources). This may worsen anemia in some individuals, as well as those who do not eat meat or meat products (vegans, vegetarians, etc.) (17).
• Drug Interactions – Resveratrol, in particular, has been found to inhibit blood clotting in lab studies. This means a high intake of resveratrol can interact with blood thinners and anticoagulants like warfarin and heparin, and NSAIDs like diclofenac, ibuprofen, aspirin, etc. (18). Close monitoring and medication adjustment may be warranted.
• Inhibit CYP3A4 Enzymes – Cytochrome P450 enzymes are involved in the metabolism of many therapeutic drugs and endogenous molecules, especially in the liver and intestines. Fresh fruit juices, frozen concentrates, or whole fruits were found to inhibit these enzymes irreversibly. This increases the risk of toxicity of several drugs by increasing their bioavailability (which is undesirable) (19).
• Kidney And Liver Failure – High doses of flavonoids like quercetin were associated with renal toxicity (kidneys) in cases where there was no history of infection, nephritis, or obstructive uropathy. Intravenous infusions of quercetin caused nausea, sweating, flushing, and vomiting in a clinical trial involving cancer patients (19).

In Summary…

Polyphenols are the most abundant antioxidants consumed by humans, and the total intake is as high as 1 g/day (16). That is because of their abundance across various food groups.

Although there are associations with adverse effects, consuming dietary polyphenols in limited amounts will be protective in the long run. Do not forget the horde of cancers these plant molecules can ward off!

Choose your favorite source(s) of polyphenols from the list we discussed above. Watch how your body feels after boosting the polyphenol content in your diet (with necessary medical advice).

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Share your feedback, suggestions, and relevant queries in the comments box below.

References

1. “The role of polyphenols in modern nutrition” Nutrition Bulletin, US National Library of Medicine
2. “A Critical Review on Polyphenols and Health Benefits…” Nutrients, US National Library of Medicine
3. “Polyphenols: food sources and bioavailability” American Journal of Clinical Nutrition, American Society for Clinical Nutrition
4. “Culinary Herbs and Spices: Their Bioactive Properties…” International Journal of Molecular Sciences, US National Library of Medicine
5. “Polyphenol-Rich Lentils and Their Health Promoting Effects” International Journal of Molecular Sciences
6. “The physicochemical composition and antioxidant actions…” Asia Pacific Journal of Clinical Nutrition, US National Library of Medicine
7. “Coffee and beverages are the major contributors to polyphenol…” Journal of Nutritional Science, US National Library of Medicine
8. “Dietary reference intake (DRI) value for dietary polyphenols…” The British Journal Of Nutrition, US National Library of Medicine
9. “Natural Polyphenols for Prevention and Treatment of Cancer” Nutrients, US National Library of Medicine
10. “Dietary Polyphenols and Obesity” Nutrients, US National Library of Medicine
11. “Polyphenol Levels Are Inversely Correlated with Body Weight…” Nutrients, US National Library of Medicine
12. “Polyphenols, Inflammation, and Cardiovascular Disease” Current Atherosclerosis Reports, US National Library of Medicine
13. “Oxidative Stress and Inflammation: What Polyphenols…” Oxidative Medicine and Cellular Longevity, US National Library of Medicine
14. “Polyphenols: Inflammation.” Current Pharmaceutical Design, US National Library of Medicine
15. “Dietary Polyphenols, Berries, and Age-related Bone Loss…” Antioxidants, US National Library of Medicine
16. “Polyphenols and gastrointestinal diseases” Current Opinion in Gastroenterology, US National Library of Medicine
17. “Risks and safety of polyphenol consumption” The American Journal of Clinical Nutrition, US National Library of Medicine
18. “Resveratrol” Micronutrient Information Centre, Linus Pauling Institute, Oregon State University
19. “Flavonoids” Micronutrient Information Centre, Linus

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Reviewer Author

Julie FreemanMA, RDN, LDN, RYT

   

Julie Freeman is a licensed integrative nutritionist with graduate education in psychology, counseling and education. Her post-graduate certifications include functional medicine, yoga, and mind-body medicine. She works closely with other health professionals to support personal transformation.

Read full bio of Julie Freeman

Swathi HandooHealth & Wellness Writer

 

Swathi holds a master’s degree in biotechnology from Osmania University and has worked in places where actual science and research happen. She has four years of experience and a Professional Certificate in Food, Nutrition & Research from Wageningen University.

Read full bio of Swathi Handoo