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Urolithin B is one of the urolithins, compounds produced by gut bacteria from the ellagitannins and ellagic acid in foods such as pomegranates, walnuts and berries. Chemically it is a monohydroxy dibenzopyranone and a downstream product of the same microbial pathway that yields urolithin A. It has been studied mainly for effects on skeletal muscle, where laboratory and animal work suggests it can promote muscle growth [1][2].
- Promotes muscle protein synthesis in preclinical models
- Reduced denervation-induced muscle atrophy in mice
- Suppressed osteoclast activity and bone loss in animal models
- Anti-inflammatory and anti-apoptotic in tissue studies
- Protected neurons against oxidative toxicity in vitro
- Comes from the same food sources as Urolithin A
Overview
Urolithin B is a phenolic compound belonging to the urolithins, metabolites formed in the gut when bacteria transform the ellagitannins and ellagic acid present in foods such as pomegranate, strawberries, raspberries, walnuts and oak-aged red wine. Structurally it is a monohydroxylated dibenzopyranone, 3-hydroxy-6H-dibenzopyran-6-one, and it is one of the simpler urolithins, carrying a single hydroxyl group [1].
Like the other urolithins, urolithin B is not obtained directly from food; it is produced by the gut microbiota during digestion of ellagitannin-rich foods and is considered a downstream product of the same microbial pathway that generates urolithin A and related metabolites [1]. After absorption it circulates largely as urolithin B glucuronide. Because the process depends on an individual's gut bacteria, the amount formed varies considerably from person to person [1].
The research on urolithin B has focused especially on skeletal muscle. In cell and animal experiments, urolithin B enhanced the growth and differentiation of muscle cells by increasing protein synthesis and reducing protein breakdown through the ubiquitin-proteasome system, and it induced muscle hypertrophy and limited muscle wasting after nerve injury in mice; these effects were associated with the androgen receptor and with signalling through the mTORC1 pathway [2]. Reviews of polyphenol-derived metabolites describe urolithin B as having a testosterone-like effect that favourably shifts the balance of muscle protein [3].
Urolithins, including urolithin B, also show antioxidant activity in cell-based assays, contributing to the antioxidant and anti-inflammatory effects attributed to ellagitannin-rich foods, although the potency of individual urolithins depends on their structure [4].
Urolithin B is not an approved drug and is encountered mainly as a research compound and, increasingly, as an ingredient in dietary supplements. The evidence for its muscle and other effects comes largely from laboratory and animal studies, and its benefits and safety in humans have not been established through clinical trials [3].
Mechanism
Urolithin B is a gut-derived of ellagitannins, and its most studied action is on skeletal muscle protein balance. In cultured muscle cells it promotes growth and differentiation by increasing the rate of protein synthesis while suppressing protein degradation through the ubiquitin-proteasome pathway, the main route by which muscle proteins are broken down; the net effect is a shift toward muscle building [2].
Mechanistic experiments implicate the in this response, with evidence of crosstalk between androgen-receptor signalling and the mTORC1 pathway that controls protein synthesis, possibly involving the energy sensor , and reviewers have accordingly described urolithin B as producing a testosterone-like effect on muscle [2][3].
In live animals, continuous delivery of urolithin B induced muscle hypertrophy and reduced the muscle atrophy that follows denervation, supporting the cell-based findings [2]. Separately, as a member of the urolithin family, urolithin B has antioxidant activity in cellular assays, which may contribute to the broader anti-inflammatory and antioxidant effects ascribed to ellagitannin-rich foods, though its structure makes it a comparatively modest direct antioxidant [4]. Because it is produced by gut bacteria from dietary precursors, the amount of urolithin B a person forms depends on their microbiome [1].
receptor fingerprint
mTORC1 signalingStimulates muscle protein synthesis, with androgen-receptor crosstalk
Ubiquitin-proteasome pathwayRepresses protein degradation machinery
NF-kB and MAPK signalingInhibits nuclear translocation and inflammatory kinase signaling
Safetyrisks and cautions, not medical advice
Urolithin B is a gut-microbiota metabolite whose safety evidence is largely preclinical, drawn from rodent studies with no dedicated human safety trials published for this specific compound. Its close relative urolithin A has been well tolerated in short human trials with no serious drug-related adverse events, mild gastrointestinal complaints (nausea, loose stools, abdominal discomfort) being the main effects, but that data does not transfer directly to urolithin B. Because human safety, long-term, and drug-interaction data for urolithin B are essentially absent, its risk profile in people is not established. As with other gut-active supplements, transient gastrointestinal effects are plausible, particularly at higher intakes.
Subjective profileweighing the evidence above
Not the one to buy. The muscle findings are interesting but entirely preclinical, and urolithin A is the sibling that actually has human trials behind it. Until someone runs a study on this compound specifically, the A form is the better use of the money.
Resources
This entry is here for reference.
Research
- 2009first citedUrolithins, intestinal microbial metabolites of Pomegranate ellagitannins, exhibit potent antio…
- 2018most recentUsing polyphenol derivatives to prevent muscle wasting
- 1.Biological significance of urolithins, the gut microbial ellagic acid-derived metabolites: the evidence so far
- 2.Urolithin B, a newly identified regulator of skeletal muscle mass
- 3.Using polyphenol derivatives to prevent muscle wasting
- 4.Urolithins, intestinal microbial metabolites of Pomegranate ellagitannins, exhibit potent antioxidant activity in a cell-based assay
4 listed here; entry last updated July 2026
Reviews
My notesprivate to this device
FAQ
Is Urolithin B the same as Urolithin A?
No. They are related gut metabolites, but Uro-A is the one tied to mitophagy while Uro-B's main finding is muscle protein synthesis; don't assume their effects overlap.
Where does it come from?
Your gut bacteria make it from ellagitannins in foods like pomegranate, walnuts and berries; not everyone produces it well.
Is there human evidence?
Very little on isolated Uro-B specifically. Almost all the current data are cell-culture and rodent studies, so treat benefits as preclinical.
When would someone take it?
Typically with meals, like the foods it derives from; there is no validated human dosing schedule.
Limitations of the evidence
- Human evidence is limited to early research
- Effects shown mainly in cells and animals
- Long-term safety in humans not established
Notes and cautions
- Gut production varies between individuals