Nutrition briefing
Polyphenols
Polyphenols are bioactive compounds made by plants. They are found in fruits, vegetables, tea, coffee, chocolate, whole grains, nuts, seeds, and spices, and they act as antioxidants, calm inflammation, and feed the bacteria in your lower gut.
What are polyphenols?
Polyphenols are plant phytochemicals: bioactive compounds produced by plants. More than 8,000 different polyphenols have been identified, and they are grouped by their structure into four main families.
Flavonoids
The largest group. Includes anthocyanins (the red and purple pigments in berries), flavanols such as EGCG in green tea, flavonols such as quercetin, plus flavanones, flavones, and isoflavones.
Phenolic acids
Includes ellagic acid (berries, pomegranate, walnuts) and a wide range of others found across fruits, vegetables, grains, and coffee.
Lignans
Concentrated in flaxseed and whole grains.
Stilbenes
The group that includes resveratrol, found in grapes, red wine, and some berries.
There is currently no official daily target for polyphenol intake. A diet rich in polyphenols, such as the Mediterranean diet, is considered beneficial for supporting a resilient gut microbiome and general health.
How polyphenols work
Polyphenols influence your health through several overlapping actions.
Antioxidant
The antioxidant action of polyphenols has been studied in humans by measuring total antioxidant capacity, superoxide dismutase, and malondialdehyde.
Anti-inflammatory
Polyphenols are thought to suppress inflammation, in part by blocking the NF-kB inflammatory pathway.
Antimicrobial
Laboratory studies suggest polyphenols can inhibit the growth of a wide range of pathogens and pathobionts.
Prebiotic
An estimated 90 to 95 per cent of dietary polyphenols reach the lower gut, so a large proportion interacts directly with the gut microbiota.
Are polyphenols prebiotics?
In 2017, the International Scientific Association for Probiotics and Prebiotics decided that polyphenols should be considered prebiotics. Because 90 to 95 per cent of polyphenols reach the lower gut, their limited absorption into the bloodstream may actually correlate with greater prebiotic effects, since more of the compound is left for your gut bacteria to use.
Polyphenol-rich foods
The simplest way to lift your intake is to eat a wide spread of plant foods across these groups. The dominant polyphenol type is noted for each item.
| Food group | Examples and serve | Dominant polyphenols |
|---|---|---|
| Berries and dark fruit | Blueberry, blackberry, blackcurrant, redcurrant, red raspberry, strawberry, sweet cherry, black elderberry, plum, pomegranate arils (1 cup, or 1/3 cup pomegranate) | Anthocyanins, flavanols, flavonols, ellagic and other phenolic acids |
| Other fruit | Apple, apricot, black and green grapes, nectarine, peach, pear, plum, prune, quince, grapefruit, orange, Kakadu plum (1 cup) | Flavanols, flavonols, flavanones, phenolic acids; grapes also carry resveratrol |
| Vegetables and legumes | Globe artichoke, asparagus, broccoli, capers, celery leaves, green and red chicory, kale, onion, parsley, shallot, spinach (1/2 cup); soy products (1/2 cup) | Flavonols (quercetin), flavones, phenolic acids; soy carries isoflavones |
| Olives and olive oil | Black and green olives (1/2 cup), extra virgin olive oil (1 tbsp) | Flavones, phenolic acids, and other polyphenols |
| Nuts and seeds | Almonds and hazelnuts, chestnut, pecan, walnut (30g), flaxseed meal (30g) | Flavanols, phenolic acids, lignans (flaxseed) |
| Whole grains | Whole grain oat, rye, wheat (1/2 cup) | Phenolic acids, lignans, flavones |
| Cocoa | Cocoa powder, dark chocolate (30g) | Flavanols, flavonols |
| Tea and coffee | Black tea, green tea, filter coffee (1 cup) | Flavanols (green tea is rich in EGCG), phenolic acids |
| Red wine | Red wine (150mL) | Anthocyanins, flavanols, resveratrol, phenolic acids |
| Dried seasonings | Cloves, rosemary, sage, thyme, turmeric | Phenolic acids and other polyphenols |
Supplement dosage guide
When food alone is not enough, specific polyphenols can be used in concentrated form to target intestinal or systemic inflammation. These are clinical doses to be used under supervision, not general recommendations. Always read the safety notes in the columns and the safety section below.
| Polyphenol | Health effect studied | Dosage | Duration |
|---|---|---|---|
| Aloe vera | May reduce intestinal inflammation | 2 x 100mL/day (aloe gel) | 4 weeks |
| Aloe vera | May reduce IBS symptoms | 500mg/day (freeze-dried gel) | 4 weeks |
| Bilberry | May reduce intestinal inflammation | 160g/day bilberry preparation (equal to about 95g dry weight, 600g fresh fruit, roughly 840mg/day anthocyanins) | 6 weeks |
| Curcumin | May reduce intestinal inflammation | 2 x 50mg/day (bio-enhanced), 2 x 1.5g/day, or 1g/day | 6 weeks to 6 months |
| Curcumin | May reduce CRP | Up to 700mg/day, not dose-dependent (most studies around 500mg) | Greatest effect at about 13 weeks |
| Curcumin | May reduce IL-6 | Not dose-dependent | Not duration-dependent |
| Curcumin | May reduce self-reported gut complaints | 500mg/day | 4 weeks |
| EGCG (green tea) | May reduce intestinal inflammation | May require more than 300mg/day (more research needed) | 28 to 56 weeks |
| EGCG (green tea) | May reduce fasting blood glucose | May require more than 300mg/day | More than 12 weeks |
| EGCG (green tea) | May reduce total and LDL cholesterol | About 200mg/day EGCG | 3 months |
| Ellagic acid | May reduce LDL cholesterol, triglycerides, fasting glucose | 180mg/day or more | 8 weeks or more |
| Ellagic acid | May reduce CRP and TNF-a | 180 to 200mg/day (up to 2 x 450mg/day for CRP) | 8 weeks to 60 days |
| Isoflavones | May improve menopausal hot flushes (frequency and severity) | 30 to 135mg/day; supplements giving more than 18.8mg genistein were more than twice as effective | 6 weeks to 12 months |
| Isoflavones (dietary soy) | May improve menopausal symptoms | About 115.9g/day soy intake, or 86g cooked soybeans | 12 weeks |
| Resveratrol | May reduce plasma TMA and TMAO | 2 x 300mg | 28 days to 8 weeks |
| Resveratrol | May reduce CRP and TNF-a | Not dose-dependent | Not duration-dependent |
| Resveratrol | May reduce blood pressure | 300mg/day, or 600 to 1000mg/day | At least 2 to 3 months |
| Resveratrol | May reduce LDL and total cholesterol | 500mg/day or more (LDL); not dose-dependent (total) | 12 weeks or more |
CRP: C-reactive protein. IL-6: interleukin 6. TNF-a: tumour necrosis factor alpha. LDL: low-density lipoprotein cholesterol. TMA: trimethylamine. TMAO: trimethylamine N-oxide.
Nutrient and drug interactions
Concentrated polyphenols are not inert. They can change how your body handles minerals, other nutrients, and a number of common medications. This is why supplement-level doses belong in a supervised plan.
Food and nutrients
Iron
Polyphenols bind iron and can reduce its absorption. 300mg of EGCG has been shown to significantly reduce iron uptake.
Folic acid
300mg of green tea extract may reduce the absorption of folic acid from a supplement.
Dietary fat
A high-fat breakfast delays and lowers resveratrol absorption. Dietary fat increases quercetin absorption.
Medications
This is not an exhaustive list. Some entries below come from animal or laboratory studies and still need confirmation in people. Tell your practitioner about every medication and supplement you take.
| Polyphenol | Medication | Effect on drug exposure |
|---|---|---|
| Curcumin | Sulfasalazine | Increased |
| Curcumin | Talinolol | Decreased |
| Curcumin | Caffeine, theophylline, clozapine, acetaminophen (not yet assessed) | Increased |
| Resveratrol | Warfarin | Increased |
| Resveratrol | Losartan, buspirone, dextromethorphan | Increased |
| Resveratrol | Caffeine | Decreased |
| Isoflavones | Theophylline | Increased |
| Isoflavones | Midazolam | Decreased |
| Ellagic acid | Metoprolol, diltiazem | Increased |
| Green tea | Simvastatin, tacrolimus, sildenafil, buspirone | Increased |
| Green tea | Rosuvastatin, nadolol, digoxin | Decreased |
| Quercetin | Cyclosporine, pravastatin, fexofenadine, paracetamol | Increased |
| Quercetin | Talinolol, midazolam | Decreased |
Safety considerations
Polyphenol-rich whole foods are safe and beneficial for almost everyone. The cautions below apply to concentrated supplements at the doses listed in the dosage guide, not to a plant-rich diet.
| Polyphenol | Maximum dose | What to know |
|---|---|---|
| Resveratrol | 150 to 450mg/day | Generally well tolerated. Gut symptoms, especially diarrhoea, are common, more so above about 2.5g/day. The EFSA panel suggests 150mg/day. Use caution with warfarin, as it may increase anticoagulant effects. |
| Ellagic acid | 2 x 500mg/day | Limited number of studies. 2 x 500mg/day has been used safely for 12 weeks with no adverse effects. |
| Curcumin | No established safe dose | A 2023 TGA report found no established safe dose and introduced new label requirements for curcumin products. Liver injury is idiosyncratic, so it cannot be predicted by dose. |
| Aloe vera | No established safe dose | Avoid products containing hydroxyanthracene derivatives (whole leaf extract or aloe latex), as there is evidence of genotoxicity. Use only the gel. |
| EGCG (green tea) | 300mg/day | Mild to moderate gut symptoms seen at 400 to 4000mg/day. Liver injury can occur with the supplement form but does not appear to occur from drinking green tea. Highest incidence is from the Polyphenon E supplement. |
| Isoflavones | No adverse effects at 300mg/day for 2 years, or 120mg/day for 3 years | In 2015 the EFSA found soy isoflavones do not adversely affect the breast, thyroid, or uterus of postmenopausal women. More research is needed on isoflavone effects on the thyroid in cases of iodine deficiency. |
EFSA: European Food Safety Authority. TGA: Therapeutic Goods Administration.
Putting it into practice
A sensible, food-first path to getting more from polyphenols.
Frequently asked questions
What are polyphenols and what foods contain them?
Polyphenols are plant compounds, with over 8,000 identified, found in foods like berries, other fruit, vegetables, olives and olive oil, nuts and seeds, whole grains, cocoa, tea, coffee, red wine and spices. They have antioxidant, anti-inflammatory, antimicrobial and prebiotic actions. Notably, around 90 to 95% of dietary polyphenols reach the lower gut, where they interact directly with the gut microbiota, which is why they were classified as prebiotics in 2017.
How are polyphenols good for the gut?
Because around 90 to 95% of dietary polyphenols reach the lower gut largely intact, they interact directly with the gut microbiota, feeding beneficial bacteria much like a prebiotic, which is why the International Scientific Association for Probiotics and Prebiotics classified them as prebiotics in 2017. Alongside this they have antioxidant and anti-inflammatory effects, including suppressing the inflammatory NF-kB pathway, so a polyphenol-rich, plant-based diet supports both the microbiome and lower inflammation.
Are polyphenol supplements safe?
Polyphenol-rich whole foods are safe and beneficial for almost everyone, and there is no official daily intake target, with a Mediterranean-style diet considered a good model. The cautions apply mainly to concentrated supplements rather than to a plant-rich diet. Some supplemental polyphenols, including curcumin, resveratrol, EGCG, quercetin and ellagic acid, can interact with medications such as warfarin, statins and antihistamines, so concentrated supplements are best used with professional guidance.
Reviewed by Rohan Smith, BHSc Nutritional Medicine · Elemental Health & Nutrition, Adelaide. Last reviewed 13 June 2026.
Important: This summary is general information, not personalised medical advice, diagnosis, or a treatment protocol. Speak with a qualified practitioner about your individual situation. Book a consultation →