Nutrition and diet

Polyphenols

Also called: plant polyphenols, flavonoids, bioactive compounds

Polyphenols are a large family of plant compounds (over 8,000 identified) that include flavonoids, phenolic acids, lignans and stilbenes. Plants make them as protection against UV, pests and oxidative stress. In the human gut, they're metabolised by bacteria into bioactive compounds that support cardiovascular health, lower inflammation, and feed beneficial microbes like Akkermansia and Bifidobacterium.

Why polyphenols matter

Bioavailability varies hugely by polyphenol class. Isoflavones and gallic acid can be absorbed at over 20%, but procyanidins, anthocyanins and most flavonoid glycosides are absorbed at well under 1%. Most dietary polyphenols therefore reach the colon, where gut bacteria break them down into smaller bioactive metabolites that can be absorbed. Different gut microbes produce different metabolites, which is one reason why individuals respond differently to the same polyphenol-rich foods. The metabolites that make it into the bloodstream have measurable effects on blood vessels, inflammation, and metabolic markers.

Highest-polyphenol foods

  • Cloves: highest polyphenol content of any common food (around 15,000 mg per 100g).
  • Cocoa and dark chocolate (70%+): 1,700-3,000 mg per 100g.
  • Berries: blackcurrant, blueberry, raspberry, blackberry, 200-1,000 mg per 100g.
  • Coffee (especially espresso): 200-400 mg per cup.
  • Tea: green tea 250-500 mg per cup, black tea 150-300 mg per cup.
  • Olives and extra virgin olive oil: 50-100 mg per tablespoon.
  • Red wine: 200-400 mg per glass (don't drink for the polyphenols, but they're there).
  • Apples, plums, cherries, citrus.
  • Onions and red cabbage.
  • Walnuts and chestnuts.
  • Soy beans and pulses.
  • Wholegrain rye and oats.

What they do

  • Feed beneficial gut bacteria preferentially, especially Akkermansia, Bifidobacterium and Lactobacillus.
  • Reduce LDL cholesterol oxidation (a step in atherosclerosis).
  • Improve endothelial function (the blood vessel lining).
  • Lower blood pressure modestly through nitric oxide pathways.
  • Reduce systemic inflammation markers.
  • Modulate insulin sensitivity in some studies.

How to actually get them

  1. Aim for 5-7 servings of plant foods a day, with as many colours as possible.
  2. Add 30 g of dark chocolate (70%+) most days. One genuinely tasty intervention.
  3. Drink coffee or green tea daily if you tolerate caffeine.
  4. Use extra virgin olive oil as your main cooking fat.
  5. Eat berries 3-5 times a week, frozen are fine.
  6. Don't take polyphenol supplements unless prescribed. They behave differently in isolation than in food.

Polyphenols vs antioxidants

Polyphenols are antioxidants in the test tube. In the human body, the picture is more complex. Most absorbed polyphenols don't reach high enough blood concentrations to act as direct antioxidants. Their main effect is signalling, switching on cellular protective pathways (Nrf2), modulating gut bacteria, and influencing inflammation. The 'antioxidant' framing in marketing oversimplifies what's actually happening.

Common questions

Should I take a polyphenol supplement?
Probably not. High-dose isolated polyphenols (resveratrol, curcumin, quercetin) sometimes work pharmacologically but aren't always benign at high doses. Polyphenols from food come with fibre, vitamins, and the right dosing range. The food-first principle holds here.
Why do polyphenols affect people differently?
Your gut bacteria decide how much benefit you extract. About 30 percent of people are 'equol producers' for soy isoflavones; the other 70 percent get less benefit from the same food. Similar variation exists for ellagic acid (pomegranate) and other polyphenols. Diversity of gut microbiome correlates with breadth of metabolism.
Is dark chocolate really good for me?
70 percent or higher cocoa content, in modest portions (20-30 g a day), is one of the better-evidenced foods for cardiovascular health, gut microbiome diversity, and even mood. Below 70 percent the sugar swamps the benefits. Don't take this as licence for a 100 g bar.
Are polyphenols destroyed by cooking?
Some are reduced (especially flavonoids in long-boiled vegetables) but many survive or even become more bioavailable. Tomato lycopene increases when cooked. Garlic alliin increases when crushed. Rough rule: a mix of raw and cooked plants gets you the broadest polyphenol profile.

Sources