Polyphenols: The Third Important Functional “P”-Foods

The third amazing functional “P”-foods is polyphenols. These are naturally occurring compounds found largely in plant-based foods such as fruits, herbs, spices, vegetables, cocoa, coffee, tea, nuts, legumes and cereals. Foods rich in polyphenols are identified by their colorful hues ranging from green color of vegetables to brown color of cloves.

What are Polyphenols?

These are secondary metabolites (chemical compounds) produced by plant in response to their harsh environment, such as ultraviolet light or pathogen attacks. Plants produce these molecules to protect them from the impacts of their environmental traits. The produced polyphenols are stored in plant tissues (root, leaf, seed, fruit, stem, flower) and are metabolically utilized by humans when the plant tissues are consumed.

At the molecular level, polyphenols are made of two structural components, the aromatic ring(s) and one or more hydroxyl group. They are classified according to the number and type of the structural components they possess.

Major Classes of Polyphenols

There are several types of polyphenols, but they are classified into four main classes according to their chemical structures. The four main classes of polyphenols are:

• Flavonoids: An example is flavan-3-ol found in tea, nuts, cocoa (dark chocolate), grapes, and legumes.
• Lignans: It’s also known as phytoestrogen and an example of lignan is enterolactone which is found in seeds, vegetables, cereals, fruits and berries. However, it’s abundant in flax and sesame seeds.
• Stilbenes: An example is resveratrol found in grapes, red wine, and berries.
• Phenolic acids: An example is syringic acid found in grape seeds, walnut, olives, dates, pumpkin pulp, and thyme.

Ranking of Different Types of Plant-Based Foods Rich in Polyphenols

A study showed the ranking of hundred foods according to their polyphenol content in milligram per 100 gram or milliliter of the food. The foods were grouped into spices, fruits, seeds, vegetables, non-alcoholic beverages, grains, cocoa products, alcoholic beverages, and oils. Here are the highly ranked polyphenol-rich foods in the groups.

Spices

• Cloves: 15,188
• Dry peppermint: 11,960
• Star anise: 5460

Cocoa products

• Cocoa powder: 3448
• Dark chocolate: 1664
• Milk chocolate: 236

Fruits

• Black chokeberry: 1756
• Black elderberry: 1359
• Lowbush blueberry: 836

Seeds

• Flax seed: 1528
• Chestnut: 1215
• Hazelnut: 495

Vegetables

• Black olive: 569
• Green olive: 346
• Globe artichoke heads: 260

Non-alcoholic beverages

• Filtered coffee: 214
• Black tea: 102
• Green tea: 89

Grains

• Whole grain hard wheat flour: 201
• Refined maize flour: 153
• Whole grain rye flour: 143

Alcoholic beverages

• Red wine: 101
• White wine: 10
• Rose wine: 10

Oils

• Extra virgin olive oil: 62
• Rapeseed oil: 17

Health Benefits of Polyphenols

Recently, the consumption of foods rich in polyphenol is advocated for because of the role they play in the prevention and management of non-communicable diseases such as cancer, cardiometabolic diseases, chronic inflammation, and so on.

The numerous health benefits of foods rich in polyphenols could be linked to the relationship between polyphenols and prebiotics, probiotics, and good microorganisms living in our digestive system. When we eat foods rich in polyphenols, our gut microbes feed and convert them into biologically active compounds that have therapeutic effects.

Some of the health benefits of eating polyphenol-rich foods include^1,2,3,4:

• Reduced risk of cardiovascular and metabolic diseases such as stroke, cardiac arrest, obesity and type 2 diabetes.
• Antioxidant and anticancer properties
• Anti-inflammatory activities.
• Reduced cholesterol.
• Insulin sensitivity.
• Reduced body mass index.
• Anti-obesogenic effects.
• Reduced osteoporosis.
• Reduced menopausal symptoms.

Bioavailability Concerns of Polyphenols

Most polyphenols are not readily bioavailable when ingested in foods. This means that they are not easily broken down and absorbed into the circulatory system to give any biological effect when we eat food rich in polyphenols.

Bioavailability of polyphenols usually depends on the origin and matrix of the food, processing parameters used for the food, the digestion process of the food, and the cellular metabolism of the food.

Notwithstanding these challenges, the following tips may help make these amazing food components readily available for potential health benefits.

• Pair polyphenolic-rich food properly to improve bioavailability. For instance, to improve the availability of curcumin in turmeric, combine turmeric and black pepper or ginger. Another example is to add lemon to your green tea.
• Gently steam your vegetables to breakdown the polyphenols in them and make them more bioavailable.
• Make your meal more colorful with variety of polyphenolic foods to maximize the availability of polyphenols in them.

Relationship Between Polyphenols, Prebiotics, and Probiotics – The Three Functional P-Foods

These three functional foods work together to elicit health benefits in humans. Polyphenols are ideal foods for probiotics and gut microbiomes.

Most foods rich in polyphenols also contain prebiotics which are also beneficial to probiotics and gut microbes and could be metabolized to bioactive compounds and vitamins by these microbes.

Polyphenols and prebiotics feed the good microbes in our guts, and these microbes in turn breakdown these food components into low molecular weight bioactive compounds beneficial to us.

Effect of Polyphenols on Bioavailability of Some Minerals

It has been reported that polyphenols affect the absorption of iron from food sources. However, when you pair your polyphenolic foods with foods rich in vitamin C, such as citrus, the bioavailability of heme-iron in the food will be greatly enhanced provided that the concentration of polyphenols is not very high⁵. It should be noted that bioavailability of iron is essential in reducing the risk of iron deficiency anemia.

Summary

Polyphenols are important dietary compounds with significant health benefits, particularly in the prevention of chronic diseases. However, their effectiveness is largely dependent on their bioavailability, which is influenced by various dietary and processing factors. Understanding these factors is crucial for maximizing the health benefits of polyphenols and designing functional foods that enhance their bioavailability.

Always include different polyphenol-rich foods in your diet to feed your gut microbiome and in turn derive the numerous health benefits thereof.

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References

1.        Alves-Santos, A. M., Sugizaki, C. S. A., Lima, G. C. & Naves, M. M. V. Prebiotic effect of dietary polyphenols: A systematic review. Journal of Functional Foods vol. 74 Preprint at https://doi.org/10.1016/j.jff.2020.104169 (2020).

2.        Rodríguez-García, C., Sánchez-Quesada, C., Toledo, E., Delgado-Rodríguez, M. & Gaforio, J. J. Naturally lignan-rich foods: A dietary tool for health promotion? Molecules vol. 24 Preprint at https://doi.org/10.3390/molecules24050917 (2019).

3.        Kumar, N. & Goel, N. Phenolic acids: Natural versatile molecules with promising therapeutic applications. Biotechnology Reports vol. 24 Preprint at https://doi.org/10.1016/j.btre.2019.e00370 (2019).

4.        Bartel, I., Mandryk, I., Horbańczuk, J. O., Wierzbicka, A. & Koszarska, M. Nutraceutical Properties of Syringic Acid in Civilization Diseases—Review. Nutrients vol. 16 Preprint at https://doi.org/10.3390/nu16010010 (2024).

5.        Ma, Q., Kim, E. Y., Lindsay, E. A. & Han, O. Bioactive Dietary Polyphenols Inhibit Heme Iron Absorption in a Dose-Dependent Manner in Human Intestinal Caco-2 Cells. J Food Sci 76, (2011).