What’s A Polyphenol?

Blog banner for National Polyphenol Day post. Background is polyphenol-rich fruits, nuts, and vegetables

July 11 is National Polyphenol Day.

But what’s a polyphenol?

You’re going to hear more about the health benefits of polyphenols, I guarantee it. Those of us in the nutrition science world have been talking about them for years. Sometimes they’re called “bioactives,” “phytonutrients,” or “antioxidants.” All of these terms are technically correct when referring to polyphenols but they are too broad. It’s like calling all people human. Yes, all people are human, but they are so much more – they are daughters and sons, musicians and dancers, writers and thinkers. All that to say, calling a polyphenol an antioxidant (or any of the other terms) and calling it a day isn’t quite fair. All that beautiful complexity also means it’s understandably a little confusing. So let me break it down.

The National Cancer Institute glossary defines a polyphenol as “a substance that is found in many plants and gives some flowers, fruits, and vegetables their color. Polyphenols have antioxidant activity.”

A research paper describes them as a plant compound that the plant itself uses to protect itself from the sun (UV damage) and diseases (e.g. caused by harmful bacteria, virus, or other micro-organisms).

Technically a “polyphenol” is a plant compound with a chemical structure that has more than one (“poly”) of a thing called a phenolic ring (i.e. a 6-carbon benzene ring with a hydroxyl (OH) group attached to it). They’re typically larger molecules, and are often broken down into smaller bits through digestion by us or our microbiome (ahem, yes, they are ideal food for our good bacteria, which makes them prebiotics; though most people are too busy talking about fiber as a prebiotic to remember polyphenols are too). I’m going to leave the biochemistry and tangent into microbiome at that. 

There are thousands of unique polyphenols we’ve identified, and likely so many more we haven’t! Just think how many different plants there are and it’s easier to comprehend that there are so many kinds of polyphenols.

Here’s what they all do, though: they stock your antioxidant defenses. It’s well-known that eating polyphenol-rich foods increases the body’s ability to respond to oxidative stress – either through being a direct antioxidant, sparing the body’s self-made store of antioxidants, or by absorbing nutrients that easily get oxidized before they can do that (e.g. iron). 

I’ve seen a few different ways polyphenols are categorized, but the most common way to think about them is in four different classes. FYI, each class can be broken down further, but we’re not going to do that today. 

  1. Flavonoids – we know the most about this type and its been studied the most. These are nature’s chemicals that make blueberries blue and daffodils yellow. Flavonoids are everywhere in fruits and veggies, whole grains, nuts, seeds, coffee, chocolate, teas, and spices.
  2. Phenolic acids – these are also quite common in foods
  3. Stilbenes – these are less common in our food, though resveratrol (found in grapes and red wine) is a quite famous stilbene
  4. Lignans – a great source of lignans is flaxseed oil

Do. Not. Worry. About. The. Specifics. Here’s why: whole foods contain a complex mixture of polyphenols. So if you are eating lots of plants, you’re all set. 

OK, OK, but if you really want to know, a “high polyphenol diet” is not well-defined in the research, but is in the 3,500-4,000 mg per day range. A cup of black tea has ~100 mg of polyphenols, a cup of blueberries has ~600 mg, and a glass of pomegranate juice has 700 mg.

If you are looking for where to start, look no further than the MIND diet, which is mostly plants and offers a wide range of polyphenols from: olive oil, red wine, berries, whole grains, leafy greens, beans, nuts, and more vegetables. But if that’s not a good fit for you – the Mediterranean diet, the U.S. Healthy Diet recommended in the Dietary Guidelines for Americans, and just about any traditional diet is going to be mostly plants – and that means polyphenols.

Why you should care: Over and over again, large population-level studies show that people who eat polyphenol-rich diets are healthier, with less heart disease, dementia – including Alzheimer’s disease, cancer, diabetes, or accelerated signs of aging.

Bottomline, and I repeat: If you are eating lots of plants, you’re all set. (and by “lots” – I mean many different kinds and plenty of them).

If you still have questions, drop them in the comments and I’ll do my best to answer simply.

 

Extra Credit:

  1. Food facts for healthy choices: Polyphenols. 2015. European Food Information Council.
  2. Polyphenol health effects on cardiovascular and neurodegenerative disorders: A review and meta-analysis. 2019. Int J Mol Sci. 
  3. Design of polyphenol-rich diets in clinical trials: A systematic review. 2021. Food Res Int.

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