By Leslie Taylor ©2025

We’ve known about plant polyphenols for quite a few years, and they’ve been studied extensively. Over 80,000 research studies have been published on polyphenols since the mid-1980s, and research continues today at a fast pace. More than 8,000 different polyphenols have been identified thus far, and we continue to discover new ones, mostly in medicinal plants and novel tropical fruits.

What is a Polyphenol?

Polyphenols are unique natural plant compounds that can be found in all plants and, typically, almost all parts of the plants—leaves, stems, barks, fruits, fruit peels or skin, seeds, and roots. Every plant contains a unique combination of polyphenols, which is why different plants and fruits, all rich in these substances, can have very different effects on the body.

All living things have inbred survival instincts. It is literally part of the cellular makeup of all species on earth. In highly mobile species like humans and other animals, the main survival instinct and mechanism is “flee, fight, or hide.” Even bacteria and virus species have learned to flee or hide from immune cells and chemical agents attacking them, as well as to fight them by mutating or changing their own physical structure to defend against them. With stationary plants rooted to the ground and incapable of physically fleeing from danger, their survival instinct is controlled by wonderfully complex and rich chemical defense mechanisms that have evolved over eons.

Plants have either created a chemical defense mechanism against what might harm them, or they have succumbed and become extinct. This is the mechanism the plants use to survive, grow, and flourish as well as to fight the many disease-causing organisms that attack them. Creating and utilizing polyphenols is one of the main mechanisms plants use to survive, grow, and flourish, to fight the many disease-causing organisms that attack them, as well as repair the damage they’ve caused.

Polyphenols are created in plants as a part of a plant’s unique biochemical immune system and antioxidant system. These chemicals reduce free radicals and prevent or repair the damage caused by free radicals that the plants are exposed to. Oxidative damage in plants can be a result of less than perfect growing conditions, soil toxins and heavy metals, too much or too little water, too much or too little sunlight, and other stressful growing conditions. Polyphenols are also the healing and repairing agents in a plant’s specialized “immune system” to overcome and heal damage by insects and browsing animals, and to protect it from various microbes like plant viruses, bacteria, fungi, and mold.

Why Rainforest Plants are so Powerful

This is why the type and number of polyphenols can vary widely in plants and the same plants can vary in polyphenol levels from one growing season to another. It really all depends on what types of damage and negative growing conditions the plants had to overcome by increasing its polyphenol content. The more stressful conditions, the higher the polyphenol content. It is also for this reason that wild-harvested plants usually have more polyphenols than cultivated plants. Growers of cultivated plants, like fruits and vegetables and even medicinal plants, control stress factors to their crops to increase harvesting yields . . . from proper irrigation, added soil nutrients, insect control, and even protection from intense sunlight. Controlling these factors will result in the plant needing to produce less stress-reducing and healing polyphenols.

These aspects also explain why tropical wild harvested rainforest plants usually have much higher amounts and more diversity in their polyphenol content than cultivated plants in the United States or Europe. The growing conditions in the tropics and in rainforests are just more intense and stressful. High humidity (which promotes more mold and fungi), intense heat and sunlight, and periods of monsoon-like rains followed by dry periods in the typical rainy-dry seasons of the tropics all contribute to the need of tropical plants to increase polyphenol production to protect themselves. And let’s not forget about the bugs! Without a cold season to kill off crawling bugs as well as bacteria, viruses, and fungi, the diversity of pests that tropical plants are exposed to are much higher in the tropics than in temperate climates. When botanists say a particular plant has “adapted” to grow in the tropics, this adaptation is usually all about the plant’s having increased its natural polyphenol production enough to survive in these more extreme growing conditions.

The consumption of exotic tropical fruits has gained in popularity in both domestic and international markets due to the growing recognition of their much higher nutritional and health-promoting effects. Fruit juices and dried fruit powders from acerola, acai, guava, graviola, camu-camu, maqui berry, passionfruit, mango, and others are showing up in many functional foods and beverages as well as in dietary supplements in the natural products industry. And it’s usually all about the powerful and high number of polyphenols these tropical fruits provide.

How Polyphenols Are Unique

The main feature that makes a polyphenol a polyphenol is its unique molecular structure, which usually makes them easy to identify. The manner in which the compound is put together molecularly facilitates a polyphenol to easily attach to and bond to other molecules and chemicals, oftentimes creating brand-new compounds. This unique molecular structure also makes polyphenols especially attracted to enzyme chemicals. However, rather than creating a new compound, they often bond to the enzyme and then disable the enzyme from performing its job, making them effective enzyme inhibitors.

For example, one of the reasons most polyphenols have antioxidant actions is that polyphenols are capable of binding with and interfering with two enzymes that are required in the complicated biochemical chain of events that creates a free radical, and especially ROS free radicals. Another good example is this: Some polyphenols are reported with weight loss or blood sugar–lowering actions because those polyphenols bond to and disable the digestive enzymes we produce during digestion that break down sugars and starches in our meals. If these enzymes don’t do their job, then the sugar and starches (and their calories) are not broken down and absorbed (raising blood sugar levels and promoting weight gain), and they are eliminated undigested. Not all polyphenols can provide this benefit/action, but some can.

Polyphenols can bind with almost any type of compound—with sugars, with other plant chemicals, and even with each other. These types of new compounds are usually called isomers or metabolites – because they are created by the body metabolizing them. For example, there are two very common natural acids found in many fruits, vegetables, and medicinal plants called caffeic acid and quinic acid. When these two chemicals bind with one another, they create new chemicals that are basically combinations or bonds between these two plant chemicals. These bonds form isomers. One very well-known isomer of caffeic and quinic acids is chlorogenic acid (CGA). So far, more than 71 different CGA compounds have been reported and are widely distributed in plants. These various compounds are just slightly different derivatives of caffeic acid bonding with quinic acid, but actions, benefits, and absorption of these derivatives can be very different.

The binding action of polyphenols can happen inside plants to make more healing and antioxidant chemicals when the plant needs them, and these bonds can happen and new chemicals are formed inside our bodies during digestion. Unbelievably, while scientists have confirmed there are more than 8,000 unique polyphenols, they estimate that between 100,000 and 200,000 metabolites of polyphenols are created in plants, animals, humans, and even microbes like bacteria. This makes it harder for scientists to study since digestive processes are so unique, very difficult to create inside a test tube, are often different in laboratory animals than in humans, and are even different among individual humans.

To make matters more complicated, some of these polyphenols are not easily digested, and they make it to the colon where we each have our own unique ratio of thousands of gut bacteria species that make up our gut microbiome. Landmark research over the last five years has shown that polyphenols interacting with bacteria in the gut microbiome make a whole host of new chemicals that contribute to many physiological functions. From chemicals that control our appetite, insulin sensitivity, fat storage, fat burning, and inflammation levels to the manufacture of neurotransmitters we need for mood, brain function, and much more, polyphenols are now thought to be the best way to modulate our gut bacteria to promote health. Some of these hard to digest polyphenols act as prebiotics or food to gut bacteria to encourage their growth and numbers.

We will probably never know the total effect polyphenols and their many isomers, derivatives, and metabolites have on promoting heath and treating diseases, but scientists agree, it’s a fascinating subject that promotes rigorous ongoing research on these important natural compounds.

The Main Actions of Polyphenols

While every natural plant chemical can have unique actions and benefits, polyphenol compounds generally share some common properties and actions. These shared actions are detailed next.

Antioxidant Actions

Almost without exception, polyphenols are widely documented as strong antioxidants. Not only can they quench free radicals, but they have cellular-protective effects to protect cells and organs from the damaging oxidation and resulting cellular damage that free radicals cause. Utilizing their binding actions with enzymes, polyphenols interfere in the chemical chain of events that’s required to make a free radical. Some polyphenols can also encourage the production of our own natural antioxidant enzymes to help address free radicals.

The powerful antioxidant nature of polyphenols has been demonstrated repeatedly in research to prevent or treat various diseases and conditions where oxidative stress is a factor in the development or progression of the disease—of which there are many. In addition, polyphenols are typically called “chain-breaking” antioxidants and are very important to add to vitamin antioxidants like vitamin C. When vitamin C lends an electron to a free radical, it becomes a pro-oxidant itself, and with two missing electrons, it can actually become a free radical, causing cellular damage until it is quenched by another antioxidant. When polyphenols lend electrons, they remain fairly stable and so prevent the initiation of further radical reactions. Polyphenols can also lend electrons to unstable vitamin C intermediates and “break the chain” reaction of vitamins turning from antioxidants to pro-oxidants to free radicals.

Anti-inflammatory Actions

The majority of polyphenols have shown some sort of anti-inflammatory action. Oftentimes inflammation is relieved or reduced simply by reducing free radicals and their damaging effects. Some polyphenols reduce inflammation by interfering in the biochemical chain of events our immune system uses to cause inflammation. This results in changes in the biochemical process where fewer pro-inflammatory chemicals are produced by the immune system and overall inflammation is reduced. This is considered an immune-regulating or immune-modulation action even though the end result is less inflammation.

Antimicrobial Actions

Many polyphenols have been shown to effectively kill bacteria, viruses, and fungi in humans, just as they do in plants. This can make some polyphenols and polyphenol-rich foods natural antimicrobial agents to aid in treating infections. These antimicrobial actions are also playing a role in the friendly gut bacteria (and not so friendly bacteria) in our gut microbiome. The antibacterial actions of polyphenols can kill off certain types of gut bacteria, yet paradoxically, other friendly bacteria are immune and use polyphenols as a food source (prebiotic) to increase in strength and numbers. Most of the gut microbiome research with polyphenols indicate they can modulate the bacterial species in a manner to treat obesity, help maintain a healthy weight more easily, reduce intestinal inflammation, and treat or prevent chronic bowel diseases such as irritable bowel syndrome and inflammatory bowel diseases.

Modulates Cholesterol & Protects Heart Function

The majority of polyphenols play a beneficial role in the biochemical processes of how the human body processes fat in the diet. This benefit is largely attributed to the antioxidant action of polyphenols and preventing the changes in the biochemical process that occur from the actions of free radicals. The effects of free radicals can result in oxidized fat cells, causing deregulated cholesterol and triglyceride levels, the promotion of clogged arteries, and heart and vein damage, leading to high blood pressure and heart diseases. A classification of antioxidants called anthocyanins are the strongest among the polyphenols that benefit the heart and cholesterol levels. For this reason, many polyphenols with these abilities are often categorized as having heart protective (cardioprotective) actions and benefits. Many studies confirm these actions reporting that polyphenols have the ability to prevent common heart diseases.

Anti-Aging Actions

A significant number of polyphenols have shown the ability to prolong the lifespan of laboratory animals in new anti-aging research. Again, free radicals are implicated in the overall aging process in both humans and animals. They can accumulate over the years in our bodies, resulting in state of chronic oxidative stress at old age. This affects not only our skin but also many internal cells, organs, and biochemical processes.

Inside most of our cells are organelles called mitochondria, and they play an integral role in biochemical processes going on inside our cells. Mitochondria, which are often called the powerhouses of cells, act like miniature factories, converting the food we eat into usable energy in the form of a chemical called adenosine triphosphate (ATP). ATP provides energy to fuel a myriad of cellular processes. If there is a biochemical process going on inside a cell, it is typically going on in the mitochondria.

Mitochondria are actually a significant generator of free radicals because free radicals are a byproduct of creating ATP. Each of our cells contain a little bit of vitamin C and antioxidant enzymes, and their role is to help deactivate these mitochondrial-produced free radicals. However, mitochondria can also be a target of free radical damage if our natural antioxidant system isn’t doing its job effectively, leading to mitochondrial dysfunction. Research now reports that mitochondrial dysfunction is one of the root causes of aging, and it helps create a state of chronic oxidative stress in the elderly. As our cells age, mitochondria lose their ability to provide cellular energy efficiently and release more free radicals, including ROS, that harm cells.

Significant research on polyphenols has reported that these naturally strong and cellular-protective antioxidant compounds can treat and relieve mitochondrial dysfunction. Restoring mitochondrial function basically renews the cell and allows it to function like it did when it was much younger. This is one method by which polyphenols can deliver an anti-aging effect and why they can prolong life in animal studies. However, another significant factor in aging is the accumulation and damage of other free–radical–like substances called advanced glycation end products (AGEs). AGEs also accumulate in our bodies, cells, and organs as we age, and are considered to be the hallmark of cellular aging. The levels of AGEs in our bodies are now thought to directly relate to how well or poorly we age, as well as which age-related chronic diseases we are at risk for.

Again, the research on these powerful polyphenols are revealing that maybe the best natural compounds on the planet that are capable of reducing AGEs and protecting cells and biochemical processes from their damaging effects are polyphenols. Thousands of studies on polyphenols report the anti-aging benefits these effective compounds can provide. Several strong polyphenols found in rainforest plants have shown in research to interfere with the formation of AGEs by binding to various chemicals required in the process of making them.

Different Polyphenols Means Different Actions

While all plants contain polyphenols, each plant has its own unique blend of these natural compounds that usually results in what each plant’s overall benefits are. With more than 8,000 polyphenols to choose from in nature, the differences between the health benefits of different plants can be the specific polyphenols a plant contains. The next clue is to look at the actions of each polyphenol and their effective dosages to achieve a benefit. Some polyphenols work at extremely low dosages of just a microgram or two to derive a benefit, and others need much higher amounts. Even common spices like cinnamon and cloves, culinary herbs like oregano and thyme, and many medicinal plants are significant sources of beneficial polyphenols, which can be greater than those found in vegetables. And, as previously discussed, tropical fruits like acerola camu-camu and acai deliver a much greater amount of polyphenols than standard cultivated fruits.

Another interesting factor concerning polyphenols is their ability to target specific kinds of cells, enzymes, molecules, and organs. Some polyphenols have an affinity to target enzymes that result in weight loss, others target cells in the cardiovascular system, and still others target other types of cells, enzymes, or organs like the brain, endocrine system, liver, skin, etc. For example, the polyphenol profile of acerola is much different from the polyphenol profile of broccoli. Acerola contains anthocyanins (and a significant amount of them), while broccoli contains little to none of this specific type of polyphenol (unless you’re eating purple broccoli). Anthocyanins have an affinity to benefit cells, organs, and enzymes in the cardiovascular system and will deliver those benefits much better than other polyphenols found in broccoli. For this reason, you’ll see many more anthocyanin-rich purple, blue, and red fruits and vegetables being marketed as “heart-healthy” supplements than many other green vegetables or yellow fruits.

All polyphenols can fight free radicals almost equally, but the affinity to specific cell types usually affects where in the body these polyphenols migrate to and relieve and repair cellular oxidation and damage caused by free radicals. Oftentimes, the best way to determine these affinities is by testing the polyphenol-rich whole plant in animals and humans. In vitro testing just confirms the initial antioxidant ability of a plant to quench free radical inside a test tube. Scientists introduce the plant to known pro-oxidant free radical molecules in a test tube and measure how much of the plant substance was required to disable and neutralize the free radicals. While this confirms a plant’s antioxidant ability, it has little to do with what actually happens inside the body (in vivo) and how these compounds get digested and where they go to interact with free radicals inside us.

These are not all of polyphenols’ actions… but it does provide a glimpse of why rainforest plants have so many documented actions and health benefits. To learn why adding polyphenols to your diet is so important, go on to the next article to learn why the average American diet is lacking in these important natural compounds.

© 2025 by Leslie Taylor. All rights reserved.

Articles in this Series:

What are Free Radicals and Antioxidants?
The Power of Polyphenols
Low Polyphenol Diets: The Hallmark of the New Western Diet
How Polyphenols Can Prevent and Treat Disease