What are Polyphenols?

We all know the wisdom: 'Eat the rainbow—plenty of fruits, vegetables, and whole grains.' But what makes plant-based foods so healthy, and why is it challenging to replicate their benefits in a supplement?

The answer lies partly in plants ' rich intrinsic polyphenol content. While we often lump them together, polyphenols can vary significantly in their structure and function.

"Other than the phenolic group and the shared biosynthetic pathway, there are few similarities among phenolic compounds,” said Michael Ganzale, Professor at the University of Alberta and a leading expert in phenolic compounds. “It is a class of several tens of thousands of phytochemicals, which vary and differ fundamentally in their structure and function."

More Than Antioxidants: Polyphenols’ Deeper Microbiome Impact

The well-known antioxidant capacity of polyphenols is often over-emphasized according to Ganzale: "The antioxidant capacity is essentially irrelevant for each and every health benefit. It's something that's easy to measure but I don't think it has any relationship to their biological function.”

Instead, many profound health benefits are mediated directly by our gut microbiome according to Ganzale: “It becomes increasingly clear that many of the health benefits of phenolic compounds are not mediated by the phenolic compounds themselves, but by microbial metabolites.”

Polyphenols interact with gut bacteria via key mechanisms of action:

• Antimicrobial Effects: Inhibiting harmful gut bacteria (e.g., proanthocyanidins¹, curcumin²)
• Metabolite Influence: Transforming into beneficial compounds like short-chain fatty acids (SCFAs) anthocyanins³ yield phenolic acids, resveratrol is metabolized⁴
• Reduced Inflamation: Lowering gut inflammation and combating oxidative stress (including isoflavones)^5,6
• Digestion Modulation: Phenolic acids (e.g., ferulic acid) bind to starch, slowing digestion for sustained glucose release and satiety⁸

Do Polyphenols Meet the Prebiotic Definition?

Polyphenol classification as prebiotics is nuanced partly because as Ganzale mentioned, the compounds are diverse in their roles and functions in the microbiome.

The International Scientific Association for Probiotics and Prebiotics (ISAPP) views them as potential prebiotics based on the Gibson et al. 2017 definition of a prebiotic, which states: "a selectively fermented ingredient that results in specific changes in the composition and/or activity of the gastrointestinal microbiota, thereby conferring a health benefit on the host."⁹

“The concept of a prebiotic is that through feeding beneficial members of the gut microbiota, a positive impact on health is created,” said Marla Cunningham, ISAPP Executive Director. “Many polyphenol compounds have been associated with health benefits, however these benefits are not necessarily through direct utilization of the polyphenol by beneficial bacteria. Polyphenols are also known to have non-prebiotic mechanisms of action, such as interacting directly with the host cells as well as having antimicrobial activity within the gut. Ongoing research and conclusions about the prebiotic nature of polyphenols will need to be compound-specific - the polyphenol family is a diverse group of compounds, containing over 10,000 structures.”

However, the Global Prebiotic Association (GPA) is embracing the potential of polyphenols in the category of prebiotics.

“GPA definition of a prebiotic, ‘a compound or ingredient that is utilized by the microbiota producing a health or performance benefit’ is appropriate for many polyphenols that have established microbiome modulating effects and associated health benefits beyond being bifidogenic or upregulating short chain fatty acids,” said Len Menoit, GPA Executive Director.

The Dietary Fiber and Polyphenol Connection

Experts including Ganzale caution that isolating polyphenols in a supplement can limit their microbiome benefits. This brings us to a crucial discovery: the inherent connection between dietary fiber and polyphenols.

“Emergent research highlights a significant synergistic relationship between fiber and bound-polyphenols, where they collectively increase fermentation and promote a more significant prebiotic effect,” said Brendan Kesler, R&D Innovation Director, Van Drunen Farms and FutureCeuticals, manufacturer of NatureKnit.

A significant benefit of fiber-bound polyphenols is the proposed protective effect of fiber, which prevents the polyphenols from breaking down en route to the colon.

“Polyphenol-bound fibers are especially beneficial for gut health because they deliver polyphenols directly to the colon, where they are released slowly and metabolized by gut microbes,” said Sagarika Banerjee, Senior Investigator - Microbiome, Nutrition & Gut Health at Givaudan. “This synergy enhances the growth of beneficial bacteria, boosts production of short-chain fatty acids, and strengthens the gut barrier. Compared to fiber or polyphenols alone, the bound form offers more targeted, longer-lasting, and powerful effects for microbiome balance and inflammation control."

Catering to the Polyphenol Push

Consumer interest in polyphenols is growing with a 39% increase in Google searches over the last year, with the topic “polyphenols and supplements” trending. The market is responding with new product launches featuring polyphenol ingredients, almost doubling (97% increase) in the past year, according to Mintel’s Global New Product Database.

“Supporting a healthy microbiome has gone mainstream because consumers recognize the link between the gut and so many other health benefits. Prebiotics, like fiber and polyphenols, also play well in personalized nutrition because of their ability to optimize a person’s unique microbiome profile,” said Brian Appell, Product Manager Health and Nutrition at Givaudan.

Fiber-bound polyphenols offer a compelling advantage to appeal to this interest as they are often derived from upcycled fruit and vegetable byproducts, aligning with consumers' growing interest in sustainability and reducing food waste. In addition, their low effective dose and superior solubility enable the incorporation into diverse products — from ready-to-mix beverages to functional bars — allowing for broad market access.

Nonetheless, the real potential of polyphenols for gut health is realized when we understand their intricate dance with dietary fiber. These fiber-bound compounds are not just passing through but actively shaping our microbiome.

References:

1. Howell, A.B. (2007). Bioactive compounds of cranberries and their role in urinary tract infection prevention. Molecular Nutrition & Food Research, 51(6), 732-737.
2. Moghadamtousi, S. Z., et al. (2014). A Review on Antibacterial, Antiviral, and Antifungal Activity of Curcumin. BioMed Research International, 2014, 186864.
3. Aura, A. M., et al. (2008). In vitro colonic metabolism of anthocyanins from bilberry (Vaccinium myrtillus L.) and blackcurrant (Ribes nigrum L.) by human fecal microbiota. Food & Function, 2(4), 183-189.
4. Walle, T. (2011). Bioavailability of Resveratrol. Annals of the New York Academy of Sciences, 1215(1), 9-15.
5. Santhakumar, M., & Battino, M. (2019). The Role of Polyphenols and Their Microbial Metabolites in Regulating Intestinal Inflammation. Antioxidants, 8(12), 629.
6. Lampe, J. W. (2009). Isoflavonoid Aglycones in Soy Foods: Impact of Metabolism by Intestinal Bacteria. Journal of the American College of Nutrition, 28(4), 438S-446S.
7. Lo, K. M., & Sze, K. H. (2014). Effects of phenolic acids on starch digestibility and glucose release in vitro. Food Chemistry, 154, 36-41.
8. Li, Y., et al. (2020). Interactions between polyphenols and dietary carbohydrates: Mechanisms and health implications. Comprehensive Reviews in Food Science and Food Safety, 19(3), 1332-1358.
9. Gibson, G.R., Hutkins, R., Sanders, M.E., Prescott, S.L., Reimer, R.A., Salminen, S.J., Scott, K., Stanton, C., Swanson, K.S., Cani, P.D., Verbeke, K., & Reid, G. (2017). Expert consensus document: The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of prebiotics. Nature Reviews Gastroenterology & Hepatology, 14(8), 491-502.
10. Based on Cryptobiotix 2024 SHIME-like in-vitro study.
11. Govaert, M., Duysburgh, C., Kesler, B., & Marzorati, M. (2025). Effects of NatureKnit™, a Blend of Fruit and Vegetable Fibers Rich in Naturally Occurring Bound Polyphenols, on the Metabolic Activity and 12. Community Composition of the Human Gut Microbiome Using the M-SHIME^®Gastrointestinal Model. Microorganisms, 13(3), 613. https://doi.org/10.3390/microorganisms13030613