Imagine you’re a plant. You can’t run away from the insects trying to eat you alive. You can’t wash off bacteria, viruses, or fungi before they can infect you. And you can’t put on SPF 50 sunscreen or a big floppy hat to protect yourself from the sun’s harmful ultraviolet rays.
What do you do to stay alive and thrive in the face of all these challenges? If you answered “synthesize polyphenols,” then congratulations! You’ve just won this round of “Are You as Smart as a Plant?”
Polyphenols are a class of compounds (a huge class, actually, made up of at least 8,000 different ones that we know of) that are in a wide variety of plant foods. You may have heard of some of them, like resveratrol (found in grapes and red wine) and EGCG (featured in green tea).
Plants produce them as protection from various threats, including disease and sun damage. And animals who consume those plants can also benefit from polyphenols in similar ways.
As industrialized societies struggle to contain multiple epidemics of chronic disease, many medical experts and researchers are now pointing to polyphenols (and other nutrients found in whole, minimally processed plant foods) as powerful allies in preventing and treating a variety of chronic conditions.
So in this article, we’ll explore the world of polyphenols, including how they work in your body, their health benefits, and whether you should get them from food or supplements.
What Are Polyphenols?
Polyphenols are natural compounds found in various plants. Researchers consider polyphenols to be kind of “bonus” compounds, or in their jargon, “secondary metabolites.” This means they’re not directly involved in the growth, development, or reproduction of a plant.
Plants produce polyphenols as a defense mechanism against ultraviolet radiation and aggression from pathogens. But they aren’t purely defensive; they’re also deployed to attract pollinators.
From our perspective, polyphenols play a significant role in the flavors and health benefits that many plant foods offer. They can change the way plants taste, and determine their colors and aromas.
Polyphenols are also antioxidants, so their presence can keep plant foods from rotting (a trick known as “oxidative stability”). They also can help prevent oxidative stress in your body after you consume them, which can help stave off many types of disease.
There are several subfamilies of polyphenols, including flavonoids, phenolic acids, and lignans. In addition to resveratrol and EGCG mentioned above, another well-studied polyphenol is curcumin, found in turmeric root and powder.
What Are the Health Benefits of Polyphenols?
The “poly” in polyphenol means that all compounds in this family have multiple phenolic hydroxyl groups — but could just as easily refer to their ability to prevent and treat multiple health conditions.
Polyphenols and Cancer Prevention
Both test-tube and animal studies suggest that polyphenols can help prevent the initiation and progression of several cancers. They do this via a number of mechanisms, including inhibiting the proliferation and spread of cancer cells, suppressing tumor growth, preventing the formation of new blood vessels, and fighting inflammation.
Different classes of polyphenols exhibit different anticancer properties. For example, flavonoids, including quercetin and kaempferol, can inhibit cancer cell growth and induce cancer cell death. Resveratrol suppresses tumor growth, inhibiting metastasis and reducing angiogenesis. And curcumin, derived from turmeric, is multitalented; it’s anti-inflammatory, antioxidant, apoptotic, antiangiogenic — and a bunch of other words that don’t begin with A.
Many forms of polyphenols are also known to influence critical signaling pathways that are integral to the initiation, advancement, and spread of cancer.
And polyphenols aren’t just cancer fighters on their own; they’re also team players. Researchers have found that polyphenol combinations are more powerful than the effects of each one individually. For example, a mixture containing quercetin, curcumin, green tea, Cruciferex (a proprietary blend of polyphenols found in cruciferous vegetables), and resveratrol significantly inhibited the growth of a particular cancer of the head and neck.
Polyphenols and Heart Health
Polyphenols can also protect your heart in a bunch of different ways. They reduce cardiac inflammation and oxidative stress, support cell mitochondria in doing their job properly, and increase survival signaling (the ways cells talk to each other when they encounter a potential threat).
Some polyphenols have also been found to reduce the formation of blood clots, which decreases the risk of heart attacks and strokes. And the flavonoid family of polyphenols promotes the dilation of blood vessels, which helps lower blood pressure and improve blood flow — both of which help with cardiovascular health.
Polyphenols can also improve your cholesterol profile — specifically, lowering LDL and increasing HDL cholesterol levels, thereby reducing the risk of atherosclerosis.
Some polyphenols are not easily absorbed by your small intestine, but it turns out that these polyphenols can be metabolized by the microbes in your gut into compounds that contribute to cardiovascular health.
Impressed by these myriad beneficial mechanisms, some researchers are now studying therapeutic protocols for using polyphenols in medicine to prevent and treat cardiovascular disease.
Polyphenols and Diabetes
One of the most dangerous consequences of diabetes can be vascular disorders, where persistent high blood sugar levels cause damage to blood vessels through inflammation, oxidation, and cell death. Polyphenols can combat all three mechanisms. And scientists are exploring how to use them to modulate the expression of the genes involved in the development of vascular conditions.
Human and animal studies (our views on the use of animals in medical research can be found here) show that polyphenols can lower high blood sugar levels and enhance the body’s ability to secrete insulin quickly and respond to it effectively.
It appears polyphenols accomplish this via several mechanisms. They slow down how quickly your body absorbs sugar from the food you eat. And they encourage your pancreas to produce more insulin in response to carbohydrate consumption. They also regulate how much glycogen the liver releases into your blood in the form of sugar.
If all that wasn’t enough, polyphenols also help insulin receptors work more efficiently and help tissues absorb more sugar than they would otherwise.
Polyphenols also fight diabetes by helping to protect pancreas cells that produce insulin from damage due to high glucose levels. They also promote the growth of these cells and slow down their death.
Polyphenols and Osteoporosis Benefits
As you age, you lose bone mass — that’s natural. But your diet and lifestyle can significantly influence the rate at which that happens. In some people, the process accelerates due to oxidative stress messing with the living tissues in bone: the osteoblasts and osteoclasts that build and break down bone, respectively.
Since polyphenols are such powerful antioxidants, researchers theorized that eating berries (one of the richest food sources of the compounds) could help reduce bone loss due to stress and aging. And they might have been on to something because several studies have now shown that people who eat a lot of berries also have higher bone mass. Since the standard pharmaceutical treatments for osteoporosis have a high rate of serious side effects, there’s a lot to be gained by exploring how eating polyphenol-rich foods can help prevent or slow bone loss.
In addition to oxidative damage, it appears that bone loss can also be caused by inflammation. A 2019 literature review found evidence that polyphenol-containing foods like fruits, vegetables, tea, and soy may combat osteoporosis by reducing inflammation, thus allowing the body’s bone remodeling process to proceed without hindrance.
A 2023 study out of Korea also found concrete evidence for the link between high polyphenol intake and protection from osteoporosis. Researchers gave bone density tests and food intake questionnaires to 4,600 women and followed up with them for an average of five years. They found that the postmenopausal women who reported eating the most phytochemical-rich foods (i.e., those high in polyphenols) had a 16% lower risk of developing osteoporosis than those who ate the least.
Polyphenols and Brain Health
One of your body’s most important functions goes by the strange name autophagy, which literally means “eating oneself.” Instead of visualizing someone chomping on their own arm, however, think of your tissues constantly absorbing and discarding malfunctioning cells, proteins, and other bits and bobs that are no longer doing their jobs. This process in the brain is key in protecting you from neurodegenerative diseases such as Parkinson’s, MS, ALS, Huntington’s, Alzheimer’s, and other types of dementia.
Research shows that polyphenols support the brain’s clean-up process by removing misfolded proteins. They also reduce brain inflammation and stress, helping protect the brain from damage that can lead to neurodegenerative conditions.
Polyphenols are especially suited to supporting your cognitive health for several reasons. First, unlike many other nutrients, they can easily pass into your brain from your bloodstream (crossing that very finicky blood-brain barrier). Second, they help to remove harmful substances known as reactive oxygen species that can damage your brain cells. Third, they can capture and neutralize certain metal ions, such as copper and iron, that could be harmful to your brain in high concentrations.
But wait — there’s more! Polyphenols have another special brain ability: They can increase the amount of neurotrophic factors in your brain that promote the health and growth of your nerve cells. By attaching themselves to the receptors of these neurotrophic factors on the surface of nerve cells, polyphenols enhance the cells’ abilities to adapt, survive, multiply, and grow. It appears, in fact, that polyphenols can not only protect your brain from degeneration but may even support learning, memory, and other cognitive abilities.
Is There an RDA for Polyphenols?
Given how awesome polyphenols are, you might think that government bodies tasked with setting nutritional standards would have come up with a recommended daily allowance (RDA). But no such standard exists in the US because the compounds aren’t considered “essential” nutrients — that is, there aren’t any diseases specifically caused by a deficit, the way insufficient vitamin C leads to scurvy and not enough B1 inevitably produces beriberi.
Instead, not getting enough polyphenols can shorten a lifespan by making a person more likely to develop one of the chronic diseases mentioned above. For example, a 2013 study found that people who consumed more than 650 milligrams of polyphenols per day had a 30% lower chance of dying in any given year compared with people who got less than 500 milligrams per day.
So instead of a numerical RDA, the quasi-governmental Food and Nutrition Board of the Institute of Medicine recommends five fruits and/or vegetables a day, which theoretically would give you a significant amount of polyphenols. And if you “eat the rainbow” pretty much every day — that is, consume foods of many different colors (and no, Skittles don’t count) — you’ll also therefore get a wide range of polyphenols.
What Foods Are Rich in Polyphenols?
What Influences Polyphenol Amounts?
Unfortunately, you can’t simply look up a food’s polyphenol content in an online database and know exactly how much you’ll get when you eat that food. And even if you could, there are various factors that can influence how much you actually absorb.
Polyphenol Bioavailability
On the whole, polyphenols tend to have low bioavailability, which means your body can absorb and use only a small percentage of what you swallow.
The exact conversion ratio is based on many factors, including the health and makeup of your gut microflora. Since your microbiome can change on a constant basis, depending on what you feed it, how much of the polyphenols in your food you can actually get into your cells may also vary widely from day to day.
Also, the different polyphenols differ greatly in how bioavailable they are. The most abundant dietary polyphenols typically have lower absorption rates than less common ones.
Food Handling Impact
How plant-based foods are processed, stored, and cooked also strongly influences their polyphenol content.
If you remove the peels and hulls of certain foods, you can lower their polyphenol content. On the other hand, macerating (such as in a blender or food processor) some foods can increase their polyphenol content.
When it comes to food storage, the cold storage of apples, pears, and onions appears to maintain high polyphenol levels. But when cut fruits turn brown, which tends to happen if they are exposed to air, they begin to lose polyphenols.
Many foods lose polyphenol levels with time. For example, in wheat flour, concentrations of polyphenols drop by about 70% after six months. But black tea actually increases its polyphenol content after some oxidation.
Some polyphenol levels also increase with cooking, while others decrease — it depends on the food, the particular polyphenolic compound, and the cooking method. For example, onions and tomatoes lose between 75% and 80% of their initial quercetin content after boiling for 15 min, and 65% after cooking in a microwave oven.
So Should You Take Polyphenol Supplements?
A limited amount of research has indicated that people may possibly see benefits from polyphenol supplements. For example, athletes who were experiencing physiological stress were given polyphenol supplements, and they experienced some benefits in performance and recovery.
But the evidence is a bit murky: Many researchers don’t use pure polyphenols or mixtures, but add in other antioxidants — so it’s hard to know how much of the benefit is coming from the polyphenols, the other active ingredients, or some synergistic interaction of multiple elements.
There’s also not a lot of safety data available about these supplements. And as polyphenol marketing gives these compounds their place in the sun, some manufacturers are taking advantage of their popularity to create mega-dose formulations that have never been tested for safety or efficacy.
Because research on the benefits of polyphenols typically uses amounts much higher than those commonly found in human diets, we just don’t know the levels at which they are safe and beneficial for human consumption.
Some supplements (including those containing polyphenols) could cause liver damage in high doses, and may also block the absorption of nonheme iron, which is an essential nutrient.
Perhaps the best argument against supplementation is that it’s probably completely unnecessary for most people, as polyphenols are abundantly available in a wide variety of fresh and healthful foods.
Plus, just like every other plant-based antioxidant and phytonutrient, polyphenols work better in harmony with other nutrients that naturally occur in food. And when you consume whole plant-based foods, you also get the benefit of fiber and other health-promoting micronutrients.
In general, most people are better off getting their nutrition from food rather than from supplements, and there’s no reason to think that polyphenols are an exception.
Polyphenol Recipes
From bitter to salty, from sweet to tart, polyphenols are in abundance in many of your favorite plant-based foods. These delicious and nourishing polyphenol recipes are a great way to experiment with and incorporate them into your daily meal routine.
1. Banana Tahini Coffee Smoothie
Coffee is a plentiful source of polyphenols as it contains chlorogenic acids, which fight free radicals and prevent oxidative stress damage, making it a potent antioxidant-rich ingredient. Not only does it give you a burst of energy — you get a powerful health boost, too! Together with creamy banana, nutty tahini, nutrient-rich cauliflower, and sweet spices, this Banana Tahini Coffee Smoothie is an easy-peasy and ultra-creamy way to enjoy polyphenols.
2. Apple Walnut Sage Dressing
Apples have an abundance of polyphenols, more specifically anthocyanins, flavanols (catechins), flavonols (quercetin, rutin), chlorogenic and caffeic acids, and dihydrochalcones, which can help to reduce inflammation, support your immune system, and even help with seasonal allergies! We don’t think you’ll need any more convincing, but this creamy Apple Walnut Sage Dressing is an inflammation-fighting, health-promoting, and deliciously sweet and savory sauce that is the perfect polyphenol-rich addition to your favorite summer or fall salad.
3. The Shine Brightly Salad
We love The Shine Brightly Salad for many reasons. And the addition of sweet and juicy blueberries is a major factor! Blueberries are loaded with anthocyanins, resveratrol, and flavonols (quercetin), which are all under the umbrella of polyphenols. You’ll also get a hefty dose of health-promoting spinach, red onion, sunflower seeds, and lemon juice. With so many colorful plant foods combined, you know you’ll be getting a wide variety of phytochemicals, antioxidants, and other polyphenols that will keep your body in tip-top shape — and shining brightly from the inside out!
Eat More Plants to Reap the Benefits of Polyphenols
From fending off cancer and heart disease to supporting healthy blood sugar levels and bone density, polyphenols are like real superheroes of our dietary choices, working tirelessly to safeguard our well-being. These compounds are readily available in a wide array of whole foods.
While some individuals may find benefit from polyphenol supplements, on the whole, the safety and efficacy of high-dose polyphenol supplements remain unclear. So it’s probably best to get your polyphenols from food. And let your plate be a canvas of color and flavor, celebrating the goodness that polyphenols have to offer.
Tell us in the comments:
- What are your favorite foods from each color of the rainbow?
- Are there polyphenol-rich foods that you’d like to add to your diet?
- Which recipe will you try next?
Featured Image: iStock.com/Aiselin82
Read Next:
- What Are Antioxidants? And What Are the Most Antioxidant-Rich Foods?
- Quercetin: Health Benefits, Risks, and Sources Compared
