What Are Ellagitannins? The Precursors to Urolithin A

Ellagitannins are the plant compounds behind pomegranate's reputation as a longevity food. On their own they are barely absorbed — their real significance is what your gut bacteria make from them: urolithin A.

What ellagitannins are

Ellagitannins are a large family of polyphenols — naturally occurring plant compounds — belonging to the broader group known as hydrolysable tannins. Chemically, they are built around a sugar core decorated with units of hexahydroxydiphenic acid, and when they break down in the digestive tract they release ellagic acid. Plants produce them as a defence chemistry, which is part of why they carry the astringent, mouth-drying character you notice in pomegranate skin, unripe fruit or strong tea. Punicalagin, the signature ellagitannin of pomegranate, is one of the most studied members of the family.

The crucial thing to understand about ellagitannins is that they are poorly absorbed as-is. When you eat a pomegranate, very little of the intact ellagitannin or even ellagic acid crosses into your bloodstream directly. Instead, these compounds travel to the lower gut, where they become raw material for your resident microbiome. This is why ellagitannins are best thought of not as an active ingredient in themselves, but as a precursor — the starting material for something the body can actually use.

How ellagitannins work: the gut conversion story

Once ellagitannins reach the colon, specific gut bacteria hydrolyse them to ellagic acid and then, through a series of steps, transform that ellagic acid into a group of metabolites called urolithins — the most notable being urolithin A. This is a genuine act of biological collaboration: the plant supplies the precursor, and your microbiome performs the chemistry your own enzymes cannot.

Here is the catch that researchers have documented repeatedly: not everyone's microbiome makes this conversion equally well. Studies grouping people by their urolithin output describe distinct 'metabotypes' — some individuals are efficient converters, others produce very little urolithin A no matter how many pomegranates they eat, because they lack the necessary bacteria. Estimates commonly cited in the literature suggest only a minority of adults convert ellagitannins into meaningful amounts of urolithin A. That single fact explains why eating ellagitannin-rich foods gives inconsistent results between people, and why taking urolithin A directly — skipping the uncertain conversion step — has become the more reliable, mechanism-led approach.

Food sources of ellagitannins

Ellagitannins are concentrated in a fairly short list of foods. If you want to raise your dietary intake of the precursor, these are the places to look:

Pomegranate — the most famous source, especially the juice, peel and membranes, thanks to punicalagin. Walnuts — among the richest nut sources, and one of the two foods most used in human research on ellagitannin metabolism. Berries — raspberries, blackberries, strawberries and cloudberries contribute meaningful amounts. Other sources — chestnuts, muscadine grapes, some oak-aged wines and spirits (from the barrel), and certain teas. Cooking and processing can reduce content, and the amount varies with variety, ripeness and growing conditions. Eating these foods is a sound part of a varied, plant-forward diet regardless of your conversion status — they bring fibre and a wider spectrum of polyphenols with them.

Benefits and what the evidence actually shows

It is important to separate the compound from its metabolite here, and to be honest about evidence strength. Ellagitannins themselves are studied largely for their antioxidant chemistry in laboratory settings; robust human outcomes attributed to intact ellagitannins are limited, precisely because they are so poorly absorbed. The more compelling human evidence sits downstream, with urolithin A, the metabolite they can produce.

On the urolithin A side, several human trials now exist and should be read as an emerging — not settled — body of work. In a first-in-human study, Andreux and colleagues (2019, Nature Metabolism) reported urolithin A was safe and well tolerated up to 1,000 mg per day and produced a mitochondrial gene-expression signature in older adults. Liu, D'Amico and colleagues (2022, JAMA Network Open) reported improvements in muscle endurance in older adults over roughly four months. Singh and colleagues (2022, Cell Reports Medicine) studied 500 mg and 1,000 mg arms in middle-aged adults over four months, examining muscle strength and exercise performance. A 2025 Nature Aging randomised trial reported support for immune-cell mitochondrial health in midlife adults over about 28 days. A systematic review in Ageing Research Reviews (2024) offers the sober framing: the human evidence is still emerging, built on relatively short trials of modest size. Preclinical work — in cells and animals, and therefore not proof of human benefit — traces back to Ryu and colleagues (2016, Nature Medicine), which first described urolithin A's effect on mitophagy and muscle function in laboratory models.

Because several of these topics touch on muscle, immune and metabolic function, a plain-language caveat is warranted: ellagitannins and urolithin A are studied for how they support normal physiological function, not as treatments. They are not intended to diagnose, treat or prevent any condition, and they are not a substitute for medical care. If you have a specific health concern, see your doctor.

Safety notes

Ellagitannin-rich foods have a long history of dietary use and are generally well tolerated; their astringency is the most noticeable everyday effect. Very high intakes of tannins can, in theory, interfere with the absorption of some minerals and may be hard on a sensitive stomach, but ordinary food amounts are not a concern for most people. As with any concentrated supplement or extract, if you are pregnant, breastfeeding, taking medication or managing a health condition, check with your healthcare provider before adding a high-dose product. Whole foods first is always reasonable advice.

Ellagitannins, urolithin A and mitophagy: the through-line

The reason ellagitannins matter for healthy ageing is the destination, not the starting point. Their value is realised only if they are converted to urolithin A, whose best-characterised role is support for mitophagy — the cellular quality-control process that recycles worn-out mitochondria so that fresher, more efficient ones can take over. Healthy mitophagy underpins mitochondrial health, and mitochondria are the cellular structures responsible for producing the energy your tissues run on. So the full chain reads: ellagitannin (from food) → gut bacteria → urolithin A → support for mitophagy → mitochondrial quality. The weak link, for most people, is the conversion step — which is exactly why supplementing with urolithin A directly, rather than relying on the precursor, has become the pragmatic choice. If you want to see the two compared head to head, our urolithin A vs ellagitannins guide lays it out.

For a fuller picture of the finished compound — the human trials, the dosing range and where the science is still early — see our best urolithin A gummies comparison and the deeper urolithin A clinical studies breakdown.

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This guide is educational and is not a substitute for advice from a qualified healthcare provider.