Ellagitannins are large polyphenolic compounds found in pomegranate, berries, nuts and some woods. When you eat these foods, the ellagitannins are hydrolyzed in the stomach and small intestine to release ellagic acid, a smaller phenolic molecule that can be acted upon by the microbes living in your colon.
Only a subset of gut bacteria can further break down ellagic acid through a stepwise series of reactions that ultimately yield urolithin A (UA). This conversion depends on the composition of your microbiota, dietary context, and even co‑administered prebiotic fibers. Understanding the microbial pathway helps explain why some people produce high levels of UA while others do not.
Key Takeaways
- Ellagitannins are hydrolyzed to ellagic acid, which reaches the colon largely unchanged.
- A defined set of gut bacteria performs stepwise dehydroxylation to turn ellagic acid into urolithin A.
- People differ in their “urolithin metabotype”; only metabotype A consistently makes urolithin A.
- Prebiotic fibers (e.g., FOS) and certain probiotic strains may boost UA production in low [14][3]‑producer individuals.
- Absorbed UA circulates as conjugated metabolites; its bioavailability is modest but biologically relevant.
Ellagitannins to Ellagic Acid: The First Chemical Shift
Ellagitannins are ester-linked polymers of hexahydroxydiphenic acid and glucose. In the acidic environment of the stomach and the enzymatic milieu of the small intestine, these polymers are cleaved, releasing free ellagic acid (EA) [1]. The released EA is poorly absorbed in the upper gut, allowing most of it to reach the colon where microbial metabolism begins.
The Core Microbial Steps: From Ellagic Acid to Urolithin A
Gut bacteria convert EA to UA through a series of dehydroxylation and decarboxylation reactions. The pathway can be simplified into three major stages:
Making urolithin A takes a chain of gut bacteria, and one in three people cannot finish it
Food ellagitannins are broken down
Free ellagic acid is rare in food. Most of it is released later by digestion and gut bacteria.
Early steps by Gordonibacter
Gordonibacter species handle early dehydroxylation steps toward urolithin A intermediates.
Other bacteria finish the job
In pure culture, Gordonibacter made intermediates but not the final urolithin A, so other gut bacteria are needed to complete it.
Output differs by person
A day after pomegranate juice, 33% of 100 healthy US adults could not convert it to urolithin A and 27% converted poorly.
Eating ellagitannin foods does not guarantee urolithin A.
Pathway steps come from lab and review evidence. The conversion split is from a trial that was industry-funded (Amazentis). Source: Singh et al., European Journal of Clinical Nutrition 2022; Selma et al., Food & Function 2014; Hu et al., Frontiers in Nutrition 2026; Alfei et al., Antioxidants 2020.
Embed this chart
Free to reuse on your site. Copy the code below; please keep the credit link.
Research note: After a single serving of ellagitannin foods, only about 2.8% (strawberries) to 16.6% (walnuts) of the ingested ellagitannins showed up as a urolithin B urinary metabolite [20].
1. Ring‑opening and dehydroxylationCertain bacteria remove hydroxyl groups from EA, producing intermediate urolithins such as urolithin M5 and urolithin C [2].
2. Further dehydroxylationAdditional bacterial enzymes strip more hydroxyl groups, generating urolithin D and finally urolithin A, which retains a single hydroxyl group on the benzene ring [3].
3. Reduction and conjugationThe final UA may be reduced to its dihydro form or conjugated with glucuronic acid or sulfate before absorption, but the core structure remains unchanged.
Key Bacterial Players and Metabotypes
Not everyone harbors the same UA‑producing microbes. Researchers have identified at least three “urolithin metabotypes” based on which urolithins appear in urine after ellagitannin consumption. Metabotype A individuals consistently produce UA as the final product, while metabotype B also makes isourolithin A and metabotype 0 makes no detectable urolithins [12][13][2].
In vitro work with gut samples from metabotype A donors showed that Gordonibacter species make urolithin intermediates in pure culture but not the final urolithin A, so other gut bacteria are needed to finish the job, and Enterocloster species carry the dehydroxylases that decide which end products are made [10][11][3]. Bacteria from a new genus in the Eggerthellaceae family make isourolithin A from ellagic acid and are tied to metabotype B, which helps explain the variability among people [12][11].
Factors That Enhance UA Production
Dietary components can shift the microbial community toward UA‑producing species. Co‑administration of fructooligosaccharides (FOS) with ellagic acid was reported to increase UA yields in one study; the size of the effect and the mechanism are not established [4].
Fermentation studies also demonstrated that adding the probiotic Streptococcus thermophilus FUA329 to fecal cultures improved UA output across different metabotypes, suggesting that targeted microbial supplementation could overcome a low‑producer status [5].
In overweight and obese adults taking pomegranate extract, blood lipid improvements appeared in the metabotype B group but not metabotype A, and some metabotype 0 people shifted to A or B [15][6].
From Colon to Circulation: Absorption and Bioavailability
Once formed, UA is absorbed primarily in the colon via passive diffusion. It appears in plasma mainly as glucuronide or sulfate conjugates, which are more water‑soluble and can circulate to peripheral tissues [7]. Absorption is modest: in a rat study with radiolabeled urolithin A, under 2.2% was absorbed, and in people most circulating urolithin A is the glucuronide conjugate [16][17].
Food matrix and digestion also matter. Simulated gastrointestinal digestion followed by fermentation of ellagic‑acid‑rich fruit polyphenols preserved the UA‑producing microbiota and resulted in higher post‑fermentation UA levels than direct EA supplementation, emphasizing the importance of whole‑food context [8].
Why Production Varies: Host and Microbial Interplay
Age, diet, medication, and health status shape the gut ecosystem. Post‑menopausal women, for example, showed different UA‑related metabolic responses when their diet was supplemented with polyphenols, highlighting that hormonal and metabolic background can modulate the microbial conversion [9].
In 100 healthy US adults given a glass of pomegranate juice, 33% could not convert it to urolithin A and 27% converted poorly. A person’s metabotype can also change with age, health status and obesity [19][18].
A person’s urolithin metabotype can change with age, health status and obesity, and a single test may misclassify someone [18][11]. Metabotype B is relatively common in overweight and obese people, while metabotype A is more frequent in normal-weight people [15].
Where to Find Urolithin A
- Double Wood Urolithin A (generic, budget-friendly)
- Mitopure by Timeline (the clinically studied branded form)
As an Amazon Associate we earn from qualifying purchases.
A Note on the Evidence
Urolithin A production varies widely among individuals; current evidence is based on laboratory and short‑term human studies, not long‑term clinical outcomes. People with gut disorders or on antibiotics should discuss dietary changes with a healthcare provider.
Frequently Asked Questions
What foods provide the ellagitannins needed for urolithin A production?
Ellagitannins are abundant in pomegranate juice and seeds, strawberries, raspberries, blackberries, walnuts, and some oak‑derived foods. Eating these foods supplies the ellagic acid precursor for microbial conversion [1].
Can I take ellagic acid supplements instead of eating whole foods?
Supplements deliver ellagic acid directly, but one simulated-digestion lab study reported more urolithin A from whole-fruit polyphenols than from ellagic acid alone; human data are lacking [8].
Why do some people not produce urolithin A even after eating pomegranate?
The absence of key bacterial strains defines metabotype 0 or B, which stops the pathway at earlier intermediates. Individual microbiota composition, diet, and recent antibiotic use are major determinants [2].
Do prebiotic fibers really increase urolithin A levels?
Possibly. One study reported that fructooligosaccharides taken with ellagic acid raised urinary UA, but this is not yet established [4].
Is urolithin A absorbed into the bloodstream?
After production in the colon, UA is absorbed as glucuronide or sulfate conjugates and appears in plasma at low concentrations. In people, most circulating urolithin A is the conjugated form, and whether conjugates act in tissues is not shown here [17][7].
Should I try probiotic supplements to become a urolithin A producer?
Specific strains like Streptococcus thermophilus FUA329 have been shown in vitro to improve UA yields when co‑fermented with fecal microbiota, but human trials are limited. Consult a healthcare professional before starting any new probiotic regimen.
References
- Saha P et al. Gut Microbiota Conversion of Dietary Ellagic Acid into Bioactive Phytoceutical Urolithin A Inhibits Heme Peroxidases. PloS one (2016). PMID 27254317
- García-Villalba R et al. Urolithins: a Comprehensive Update on their Metabolism, Bioactivity, and Associated Gut Microbiota. Molecular nutrition & food research (2022). PMID 35118817
- He F et al. In vitro conversion of ellagic acid to urolithin A by different gut microbiota of urolithin metabotype A. Applied microbiology and biotechnology (2024). PMID 38363367
- Zhang L et al. Fructooligosaccharides and ellagic acid synergistically enhance muscular endurance via targeting gut microbial urolithin A biosynthesis. Journal of advanced research (2026). PMID 41506451
- Xia M et al. Improvement of Urolithin A Yield by In Vitro Cofermentation of Streptococcus thermophilus FUA329 with Human Gut Microbiota from Different Urolithin Metabotypes. Journal of agricultural and food chemistry (2024). PMID 38301119
- Cortés-Martín A et al. Urolithin A production drives the effects of pomegranate on the gut microbial metabolism of bile acids and cholesterol in mild dyslipidaemic overweight and obese individuals. Food & function (2024). PMID 38329279
- Yuan H et al. Urolithin A From Gut Metabolite to Therapeutic Agent: Bioavailability, Mechanisms, and Translational Insights. Journal of food science (2026). PMID 41866331
- Xie Z et al. Bioactive release and modulation of urolithin metabotype A phenotype gut microbiota during in vitro digestion and fermentation of ellagic acid-rich fruit polyphenols. Food & function (2025). PMID 40679425
- Jarrín-Orozco MP et al. Precision health targeting TMAO in postmenopausal women: polyphenol effects modulated by urolithin A and equol metabotypes in a randomised, placebo-controlled crossover trial. Food & function (2026). PMID 41642121
- Selma MV et al. Description of urolithin production capacity from ellagic acid of two human intestinal Gordonibacter species. Food & function (2014). PMID 24909569
- Lingmin Hu et al. Urolithins in clinical translation: from gut microbial metabolites to precision interventions. Frontiers in Nutrition (2026). PMID 42626640
- Maria Victoria Selma et al. Isolation of Human Intestinal Bacteria Capable of Producing the Bioactive Metabolite Isourolithin A from Ellagic Acid. Frontiers in Microbiology (2017). PMID 28824607
- Francisco Abraham Tomás-Barberán et al. Ellagic Acid Metabolism by Human Gut Microbiota: Consistent Observation of Three Urolithin Phenotypes in Intervention Trials, Independent of Food Source, Age, and Health Status. Journal of Agricultural and Food Chemistry (2014). PMID 24976365
- Napier BA et al. Multi-Species Synbiotic Supplementation Enhances Gut Microbial Diversity, Increases Urolithin A and Butyrate Production, and Reduces Inflammation in Healthy Adults: A Randomized, Placebo-Controlled Trial. Nutrients (2025). PMID 40944126
- Sheng Wu et al. Diverse Phytochemicals and Bioactivities in the Ancient Fruit and Modern Functional Food Pomegranate (Punica granatum). Molecules (2017). PMID 28946708
- U.S. Food and Drug Administration Agency Response Letter GRAS Notice No. GRN 000791. U.S. Food and Drug Administration (2018). source
- Liu S et al. Effect of Urolithin A Supplementation on Muscle Endurance and Mitochondrial Health in Older Adults: A Randomized Clinical Trial. JAMA network open (2022). PMID 35050355
- Silvana Alfei et al. Oxidative Stress, Antioxidant Capabilities, and Bioavailability: Ellagic Acid or Urolithins?. Antioxidants (2020). PMID 32759749
- Singh A et al. Direct supplementation with Urolithin A overcomes limitations of dietary exposure and gut microbiome variability in healthy adults to achieve consistent levels across the population. European journal of clinical nutrition (2022). PMID 34117375
- Begoña Cerdá et al. Metabolism of Antioxidant and Chemopreventive Ellagitannins from Strawberries, Raspberries, Walnuts, and Oak-Aged Wine in Humans: Identification of Biomarkers and Individual Variability. Journal of Agricultural and Food Chemistry (2004). PMID 15656654
These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure, or prevent any disease. Content is for informational purposes only and is not medical advice; consult a qualified healthcare provider before starting any supplement. As an Amazon Associate we earn from qualifying purchases.