Pentadecanoic acid (C15:0, usually shortened to C15) is a saturated fatty acid with 15 carbons. Most dietary fats have an even number of carbons, and that single extra-or-missing carbon is the starting point for nearly every mechanism proposed for it. This page walks through what is known about how C15 is handled by the body, which receptor and pathway claims rest on cell studies, which have animal support, and what has actually been measured in people.
One fact runs through all of it: much of the mechanism research comes from scientists employed by Epitracker and Seraphina Therapeutics, which hold licensing rights to commercialize C15 and sell the Fatty15 supplement. Their papers disclose this. We point out which findings come from that group and which come from independent labs, because it changes how much weight a result can carry.
Key Takeaways
- The best-established mechanism is chemical: breaking down C15 releases propionyl-CoA, which can refill the citric acid cycle. That is textbook biochemistry, not a supplement claim.
- Receptor claims (PPAR-alpha and PPAR-delta, AMPK, mTOR, HDAC6) come mainly from cell assays. One independent muscle-cell study supports the AMPK route.
- The headline comparisons with omega-3, rapamycin and metformin are similarity scores across cell panels, run by the company that sells C15. They are not clinical comparisons.
- Ferroptosis and “cellular fragility” are a hypothesis from one author, with some independent animal data on liver fibrosis.
- The one randomized trial of a C15 supplement alone measured blood C15 and safety over 12 weeks, not these mechanisms.
Start With the Chemistry: Why an Odd Chain Matters
Fatty acids are burned two carbons at a time. An even-chain fat such as palmitic acid (16 carbons) ends as acetyl-CoA units only. An odd-chain fat such as C15 leaves a three-carbon piece at the end, propionyl-CoA. Propionyl-CoA is converted to succinyl-CoA, an intermediate of the citric acid cycle, so C15 can top up the cycle’s intermediates rather than only feed it fuel. This top-up is called anaplerosis. A 2016 review from Germany’s Max Rubner-Institut sets out this route and notes that C15 and C17 can also be lengthened into very-long-chain fatty acids (23 and 25 carbons) found in brain glycosphingolipids.[1]
The same review makes a point that complicates the “you can only get it from dairy” story: the body can make odd-chain fats itself, for example from propionate produced by gut bacteria.[1] A 2015 review from the UK Medical Research Council added that the ratio of C15 to C17 in human plasma is roughly 1:2, the reverse of the roughly 2:1 ratio in dairy fat, which suggests at least some circulating odd-chain fat is made in the body, possibly through a process called alpha-oxidation.[2] In mice, gut bacteria changed how much odd-chain fat the liver made, but the effect depended on how much propionate the diet already supplied.[3] For more on dietary intake, see our guide to C15 food sources.
The fiber route is not settled in people. A small crossover trial found a week of inulin raised blood pentadecanoic acid by about 17%, but two other small human studies found that fiber supplements or a high-fiber diet did not raise circulating odd-chain fatty acids [27][28].
The Propionyl-CoA Route: What a Related Medicine Shows
The strongest evidence that odd-chain fats can matter for energy metabolism does not come from C15 at all. It comes from triheptanoin, a triglyceride built from three 7-carbon fatty acids, used in people with inherited long-chain fatty acid oxidation disorders. In a retrospective chart review of 20 patients treated for up to 12.5 years, hospital days per year fell by 67% after starting triheptanoin (5.76 vs 17.55), and in the 9 patients with low blood sugar episodes those events fell by 96%. The authors noted that the study was retrospective and called for prospective trials.[4] A later review summarized fewer low-blood-sugar events and better heart function, with a smaller effect on muscle symptoms.[5]
Research note: In mice lacking the enzyme Hacl1, blood and liver C17:0 were roughly a quarter lower while C15:0 was unchanged: evidence that C17:0, but not C15:0, is partly made in the body via alpha-oxidation [31].
In a mouse model of Alzheimer’s disease, dietary triheptanoin for four and a half months lessened brain ATP loss and mitochondrial dysfunction and preserved synapse density, without changing amyloid plaques.[6]
Two cautions keep this in proportion. Triheptanoin is a 7-carbon fat used as a major energy source in a specific genetic disease, so it shows the pathway can matter, not that a 100 to 300 mg C15 capsule moves it in a healthy adult. And odd-chain markers do shift with age: in 163 healthy people aged 20 to 90, many odd-chain acylcarnitines (the form fatty acids take on their way into mitochondria) were lower in older participants, though the authors could not say whether that reflects decline or adaptation.[7]
Receptor and Signaling Targets
A 2025 review of the mechanism literature lists the targets most often claimed for C15: it is described as a dual partial agonist of the nuclear receptors PPAR-alpha and PPAR-delta, it activates AMPK (a cellular energy sensor), suppresses mTOR (a growth-signaling hub), selectively inhibits the enzyme HDAC6, supports succinate-driven respiration at mitochondrial complex II and dampens IL-6 driven JAK2/STAT3 and NF-kB signaling.[8] The review also states that prospective clinical outcomes are still lacking. Its author discloses founding a supplement company that has explored C15 products.
The proposed ways C15 works come from cells and enzyme tests, not from people
Broad activity, shared with rapamycin
At 17 µM, C15:0 had 36 activities in 10 of 12 cell systems and shared 24 activities with rapamycin.
Cannabinoid receptors
Pentadecanoylcarnitine, a C15 metabolite, acted as an agonist at CB1 and CB2 receptors (EC50 3.7 and 3.2 µM).
Two enzymes inhibited
C15:0 inhibited FAAH (IC50 2.5 µM) and MAO-B (IC50 19.4 µM).
Glucose uptake via AMPK
Pentadecanoic acid promoted glucose uptake through the AMPK pathway in cultured cells.
These are leads for researchers, not proof that a capsule does any of this in your body.
All four results are lab experiments. Several come from industry-funded groups. Source: Nutrients 2023; Scientific Reports 2022; International Journal of Molecular Sciences 2025; Food & Nutrition Research 2021; World Journal of Biological Chemistry 2025.
Chart: c15hub.com: The proposed ways C15 works come from cells and enzyme tests, not from people
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“Partial agonist” means C15 switches the receptor on, but to a lower ceiling than drugs such as fibrates. That is often presented as a safety advantage. It also means effects depend on dose and on what else is signaling to the same receptor, which is one reason cell results do not translate directly to a capsule.
The AMPK claim has independent support. A 2021 study from East China Normal University found that C15 increased glucose uptake in mouse muscle cells and moved the GLUT4 glucose transporter to the cell surface. Blocking AMPK with an inhibitor reversed the effect, while the insulin-signaling pathway itself was unchanged.[9] That is a cell-culture result, but it comes from a group with no stated conflict of interest.
PPAR activation is not automatically good news, either. In pregnant mice fed 1% C15, liver PPAR-alpha and MAPK signaling increased, and the mothers developed mild insulin resistance, while their offspring grew faster and had lower blood and liver triglycerides.[10] It is also worth remembering that C15 is one of many dairy components proposed to act on PPAR, mTOR and related pathways, alongside specific amino acids, other fats, probiotics, vitamin K and calcium.[11]
Cell-Panel Screens: What the Comparisons Actually Measured
Two widely quoted C15 claims come from a commercial screening platform (BioMAP) that exposes 12 types of primary human cells to a compound and measures 148 biomarkers. In a 2022 paper, C15 at four concentrations (1.9 to 50 µM) was not toxic to cells and had anti-inflammatory and antiproliferative activity across 36 biomarkers in 10 of the 12 systems. EPA, an omega-3 fatty acid, was toxic to four systems at 50 µM.[12]
A 2023 paper compared C15 with three compounds studied for longevity: acarbose, metformin and rapamycin. At 17 µM, C15 shared 24 activities with rapamycin across 10 cell systems, including lower MCP-1 and TNF-alpha.[13]
These results describe how similar the pattern of biomarker changes is in cultured cells. They do not show that C15 does what rapamycin or an omega-3 supplement does in a person, and both papers were written by authors employed by or consulting for the companies that commercialize C15. The same 2022 paper reported that C15’s profile resembled an antidepressant, two antimicrobials and two chemotherapy drugs at different concentrations, which shows how broad these similarity scores are.[12]
Membranes, Ferroptosis and the Cellular Stability Hypothesis
Ferroptosis is a form of cell death driven by iron and the oxidation of fragile fatty acids in cell membranes. In 2024, Epitracker’s founder proposed the “Cellular Stability Hypothesis”: that C15 stabilizes membranes and supports mitochondria, that membranes need more than 0.4% to 0.64% C15 for long-term health, and that levels at or below 0.2% of circulating fatty acids amount to a deficiency she names “Cellular Fragility Syndrome.”[14] This is a hypothesis paper by a single author with a commercial interest, and the thresholds have not been tested in an independent trial.
Independent results do not all favor the membrane idea. In fission yeast, C15 was built into membrane lipids and formed abnormal endoplasmic reticulum sheets that blocked cell division, and in human muscle samples pentadecanoic acid had accumulated in people with sarcopenia and triggered cell-death signalling in cell work. Both are early findings, but they show that entering membranes is not automatically stabilizing [29][30].
Earlier work from the same group reported that C15 reduced inflammation, anemia, abnormal blood lipids and fibrosis in animal models and proposed it as a potential essential fatty acid.[15] Independent animal studies point the same direction on some of these measures. In rats given a liver toxin for 9 weeks, oral C15 at 10, 20 and 40 mg/kg a day lowered liver enzymes, collagen build-up and iron accumulation, and reduced markers of fibrosis and inflammation including TGF-beta1, NLRP3, NF-kB and HDAC6.[16] In two mouse models of inflammatory bowel disease, a group at Case Western Reserve University found less ileitis and better-preserved gut barrier function with C15.[17] See C15 and inflammation and C15 and liver health for the full evidence on those topics.
A 2025 Epitracker study added a brain angle: in a third-party screening panel, C15 inhibited two enzymes, fatty acid amide hydrolase (half-maximal inhibition at 2.5 µM) and monoamine oxidase B (19.4 µM).[18] The dolphin side of that work is covered in the C15 discovery story.
Pentadecanoylcarnitine: A Metabolite With Its Own Targets
When C15 is carried into mitochondria it is attached to carnitine, forming pentadecanoylcarnitine. A 2022 Epitracker study tested this metabolite directly and reported that it fully activated both cannabinoid receptors, CB1 and CB2, at half-maximal concentrations of 3.7 and 3.2 µM. It also acted on two serotonin receptors and blocked two histamine receptors, and it lowered several inflammatory markers in five cell systems. The authors called it the second full-acting endocannabinoid to be discovered.[19]
Context helps here. The body’s best-studied endocannabinoid, 2-AG, is the one usually described as a full agonist at both receptors.[20] In a 2000 receptor study, 2-AG reached half-maximal CB2 activation at concentrations in the nanomolar range, about 122 nM in one assay.[21] The assays differ, so this is not a head-to-head comparison, but micromolar concentrations are a thousand times larger than nanomolar ones. Pentadecanoylcarnitine also circulates at very low levels; a lab method paper describes it as occurring at very low concentrations in plasma and tissues.[22] Whether a C15 supplement raises it enough to matter at these receptors has not been measured.
Is C15 an Essential Fatty Acid?
The mechanism work is the basis for the claim that C15 is a third essential fatty acid. Epitracker proposed it in 2020.[15] An independent 2024 review from a French research group concluded that C15 “might” meet both criteria for essentiality but that further investigation of both is needed.[23] The same group then fed C15 to rats raised on a diet lacking the established essential fats. C15 improved early growth, as linoleic acid did, and the rats made a previously undescribed family of odd-chain polyunsaturated fats; the authors say the mechanism still has to be worked out. That PhD work was funded by the French dairy industry body.[24] The case against, including evidence that the body makes some odd-chain fat itself, is covered in our full review of the essential fatty acid claim.
What Has Been Measured in People
The human evidence does not yet test these mechanisms directly. The first randomized trial of a C15 supplement on its own gave 30 young adults with overweight or obesity 200 mg a day or placebo for 12 weeks. Its primary outcome was the change in blood C15, which rose by 1.88 µg/mL more than on placebo, and there were no significant adverse events. Participants who finished above 5 µg/mL had larger drops in liver enzymes and a larger rise in hemoglobin, a post-hoc observation the authors say warrants further study.[25] The TANGO trial tested C15 alongside a Mediterranean-style diet in women with fatty liver.[26] Neither trial measured PPAR activation, ferroptosis markers or pentadecanoylcarnitine signaling. For safety data, see Fatty15 side effects and safety.
That 12-week trial was supported by Seraphina Therapeutics, which supplied the capsules, and apart from a drop in the liver enzyme GGT it found no other significant secondary changes versus placebo. In TANGO, both diet groups lost weight and liver fat, and C15 added a further reduction in LDL cholesterol only [25][26].
How to Read a C15 Mechanism Claim
- What was tested? Cells, animals and people answer different questions. A cell result says a pathway can respond, not that it does at supplement doses.
- At what concentration? Micromolar effects in a dish need to be compared with blood levels actually reached, which the 2024 trial reports in µg/mL.
- Who ran it? Results from Epitracker and Seraphina authors are disclosed as such. Look for the same finding from an unaffiliated lab.
- Was it replicated? One study of a new mechanism is a lead, not a conclusion.
- Does the claim match the paper? “Shares activities with rapamycin” in a cell panel is very different from “works like rapamycin.”
🛒 Where to Buy Pentadecanoic Acid (C15)
- Fatty15 (official site) 20% off with code SFKKDBQQ
capsules, 100 mg C15 per capsule; 1 capsule/day starter, 2 capsules/day maintenance: Category creator, from the original Epitracker research team (Venn-Watson et al.); uses a patented, sustainably-sourced pure C15 ingredient; most expensive per-capsule but reference product for all comparisons - Double Wood Supplements Pentadecanoic Acid C15
capsules, 200 mg C15 per serving (2 capsules): Generic C15 supplement; significantly lower price than Fatty15; no independent clinical trials on this specific product; good option for budget-conscious buyers who want to trial the fatty acid - Sports Research Pentadecanoic Acid C15
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powder, 100 to 300 mg per measured serving: Most economical option for higher-dose protocols or stackers; requires a milligram-accurate scale; no excipients or additives; not recommended for beginners unfamiliar with powder dosing
As an Amazon Associate we earn from qualifying purchases. C15 products vary widely in how much pentadecanoic acid they actually contain, so check that the Supplement Facts panel lists C15 in milligrams as its own line item rather than bundling it into a fatty acid blend, and that the per-serving dose falls in the 100 to 300 mg range used in published research.
A Note on the Evidence
The mechanisms described here rest mostly on cell and animal studies. Several of the most cited papers were written by people employed by, or holding equity in, companies that sell C15. The randomized human evidence is small and did not measure these pathways. No regulator has evaluated C15 for preventing or treating any disease. If you are pregnant, nursing, managing a chronic condition or taking medication, talk to a clinician before adding a fatty acid supplement.
Frequently Asked Questions
What makes C15 different from other saturated fats?
It has an odd number of carbons. When it is broken down, the last piece is propionyl-CoA, which can refill the citric acid cycle. Even-chain fats such as palmitic acid end only as acetyl-CoA.[1]
Is C15 a PPAR agonist?
It is described as a partial agonist of PPAR-alpha and PPAR-delta, based mainly on cell assays summarized in a 2025 review. Partial means it activates the receptor to a lower ceiling than fibrate drugs. Whether supplement doses do this in people has not been measured.[8]
Has C15 been shown to work like rapamycin or metformin?
No. A company-funded cell-panel study found that C15 at 17 µM shared 24 biomarker activities with rapamycin. That is a similarity in cultured cells, not evidence of the same effects in people.[13]
Is pentadecanoylcarnitine a real endocannabinoid?
One 2022 study by the company that sells C15 found it fully activated CB1 and CB2 receptors at micromolar concentrations. It has not been independently confirmed, and the established endocannabinoid 2-AG acts at much lower concentrations.[19][21]
Has any human trial measured these mechanisms?
Not directly. The 12-week randomized trial of 200 mg a day measured blood C15, safety and routine lab values, not receptor activity or ferroptosis.[25]
References
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- Weitkunat K et al. Effect of Microbial Status on Hepatic Odd-Chain Fatty Acids Is Diet-Dependent. Nutrients (2021). PMID 34064336
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- Sklirou E et al. Physiological Perspectives on the Use of Triheptanoin as Anaplerotic Therapy for Long Chain Fatty Acid Oxidation Disorders. Frontiers in Genetics (2021). PMID 33584796
- Yuan X et al. Triheptanoin Mitigates Brain ATP Depletion and Mitochondrial Dysfunction in a Mouse Model of Alzheimer’s Disease. Journal of Alzheimer’s Disease (2020). PMID 33016909
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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.