Pentadecanoic acid, or C15:0, is a 15-carbon saturated fatty acid whose supplementation has not been shown to prevent diabetes or extend life. In a trial involving 30 young adults, 200 mg a day for 12 weeks mainly increased its blood levels: this is not a validated effective dose.
The key update has two parts: an initial trial using 200 mg a day confirms that blood levels rise, while a cardiovascular analysis published in 2026 finds no evidence of causality despite some favorable associations.
What is C15:0?
C15:0, or pentadecanoic acid, is an odd-chain saturated fatty acid with fifteen carbons. It is also called pentadecylic acid, or pentadecanoic acid in English. The zero denotes the absence of double bonds: it is not an omega-3. It is present in small amounts in ruminant fats, some dairy products and some fish.
Its odd-numbered chain changes the final stage of its beta-oxidation. Unlike an even-chain fatty acid, which produces only acetyl-CoA, C15:0 also generates propionyl-CoA, which can then be converted into succinyl-CoA.
This biochemical mechanism is real. It does not prove that taking C15:0 boosts perceived energy, repairs mitochondria or extends life. A Krebs cycle intermediate is not a clinical outcome.
Why C15:0 attracted attention
In the European EPIC-InterAct cohort, researchers compared plasma fatty acids in 12,403 people who developed type 2 diabetes and a subcohort of more than 16,000 participants. A one-standard-deviation increase in C15:0 was associated with a lower risk of diabetes, with a hazard ratio of 0.79.
This signal deserves investigation as an association. The hazard ratio of 0.79 compares blood concentrations: it is neither an absolute risk reduction nor “21% less diabetes thanks to a capsule.”
It does not answer three essential questions:
- is C15:0 itself protective?
- does it instead represent certain foods or lifestyle habits?
- does it reflect endogenous production linked to fiber and the microbiome?
A favorable blood concentration can be a marker without being the cause of the benefit. Supplementing the marker does not necessarily reproduce the lifestyle it represents.
C15:0 does not come only from dairy products
C15:0 and C17:0 have long been used as biomarkers of dairy fat consumption. Their origin is less exclusive than previously thought.
In a crossover trial involving 16 adults, seven days of inulin or propionate increased plasma odd-chain fatty acids. Associated cell experiments supported liver synthesis from propionate produced by intestinal fermentation.
This changes how cohorts are interpreted. A high level can reflect dairy products, other foods and a diet rich in fermentable fiber. It becomes harder to attribute the association to dietary C15:0 alone.
Is C15:0 really essential?
An essential nutrient must meet more criteria than a plausible mechanism. In particular, evidence must show that the body cannot produce enough of it, that insufficient amounts cause a reproducible impairment and that intake corrects that impairment.
The often-cited 2020 publication proposed C15:0 as a “potential essential fatty acid.” It combined cell data, animal models and human associations. It did not demonstrate a deficiency syndrome in humans.
The conflict of interest is central to interpreting this conclusion. The lead author was a cofounder and employee of Epitracker and Seraphina Therapeutics. These companies funded the research and held commercialization rights for odd-chain fatty acids. Another author served on the scientific advisory board and held shares.
A disclosed conflict does not invalidate the data. It does require separating the experimental findings from the commercial proposition. The sources reviewed establish neither a dietary reference intake specific to C15:0 nor a clinically agreed deficiency threshold. Discovering cellular effects does not turn an entire population into deficient patients.
What dose of C15:0 has been studied in humans?
In 2024, a double-blind randomized trial included 30 young adults with overweight or obesity. Twenty received 200 mg of C15:0 a day and ten received a placebo for twelve weeks.
The primary outcome was met: circulating C15:0 increased more with the supplement. No significant adverse events were reported in the abstract. This small sample size and short duration cannot rule out a rare risk.
The authors then observed that participants reaching a final concentration above 5 µg/mL had greater decreases in certain liver enzymes. This analysis based on the level reached is not the main randomized comparison and may be influenced by other differences between participants.
The study does not demonstrate the following outcomes:
- prevention of diabetes or cardiovascular disease
- clinically meaningful weight loss
- improved longevity
- an optimal dose of 200 mg
- safety beyond twelve weeks
The project received NIH support. Seraphina Therapeutics also supported the study and supplied the supplements and placebos. This disclosure must accompany any interpretation.
Does the TANGO trial provide additional evidence?
The TANGO trial assigned 88 Chinese women with fatty liver to an adapted Mediterranean-style diet with C15:0, the same diet without C15:0, or their usual diet.
After twelve weeks, liver fat measured by MRI had decreased by 33% with diet plus C15:0, by 30% with diet alone and by 10% in the control group. These relative changes alone do not demonstrate that the supplement is superior to diet alone for liver outcomes. Adding C15:0 was associated with a further reduction in LDL cholesterol and a change in the microbiome.
The primary outcome remains dominated by the dietary intervention and weight loss. It does not allow the overall liver improvements to be attributed to C15:0 or generalized to the healthy population. The trial on tomatoes and fatty liver raises a related question: what does an improvement in liver fat actually measure?
The 2026 cardiovascular update
An analysis of the CARDIA and ARIC cohorts published in 2026 examined links between plasma C15:0, blood pressure and cardiovascular events. Higher concentrations were modestly associated with lower blood pressure and less hypertension.
However, C15:0 was not associated with incident cardiovascular events or the measures of cardiac function studied. A Mendelian randomization analysis provided no evidence supporting a causal effect on blood pressure or hypertension.
This study does not prove that C15:0 is useless. It weakens the claim that directly increasing its level would protect the heart.
Benefits, strength of evidence and decisions
| Claim | Best human evidence | Current conclusion |
|---|---|---|
| Diabetes prevention | Cohorts and observational meta-analyses | Consistent association, causality not established |
| Liver health | Small supplementation trial and TANGO dietary trial | Exploratory signal, dietary intervention difficult to separate out |
| Cholesterol | Additional LDL reduction in TANGO | Needs confirmation in a trial focused on C15:0 |
| Cardiovascular health | CARDIA and ARIC cohorts plus Mendelian randomization | Modest associations, no evidence of causality |
| Longevity | Cells and animals | No human clinical evidence |
| Correcting a deficiency | No recognized syndrome | Essential status not established |
The same reasoning applies to other early-stage longevity compounds. The article on fisetin and the lack of a validated human dose · FR shows why an appealing mechanism is not enough to build a protocol.
What about C15:0 risks, interactions and quality checks?
The dose of 200 mg a day for twelve weeks comes from a trial, not a recommendation. An amount printed on a label does not prove that it prevents disease.
No plasma or red blood cell threshold has been validated for deciding that someone is “deficient.” Values proposed by a brand may help sell a test and its supplement without constituting a medical standard.
Safety data remain limited:
- only thirty participants in the direct trial
- twelve weeks of follow-up
- little data on rare events
- interactions and long-term effects insufficiently characterized
C15:0 is still a saturated fatty acid, but that alone justifies neither declaring it inherently dangerous nor declaring it cardioprotective. Situations requiring professional advice beforehand are listed in the Verdict.
Which foods contain pentadecanoic acid?
Dairy fats, ruminant fats and some fish provide it. Their content depends on the food and its fat content: there is no universal serving to eat to “correct” a blood level.
| Source | What we can say | Practical decision |
|---|---|---|
| Dairy products that retain their fat | Dietary source of C15:0 | Choose them as part of your overall diet, not as treatment |
| Ruminant fats | C15:0 is present among many fatty acids | No reason to increase butter or meat for this marker alone |
| Some fish | Intake varies by species and product | Do not confuse C15:0 with omega-3 |
| Fermentable fiber | Indirect source of propionate enabling endogenous synthesis | A metabolic pathway, not the food’s C15:0 content |
Cheese, yogurt and a capsule are not equivalent interventions. Foods also provide protein, calcium, sodium, other fatty acids and energy. Our guide to fermented cheeses and the evidence for their health benefits examines the food matrix, a different question from isolated C15:0.
If you eat dairy products and tolerate them, choose them based on your overall diet and preferences. If you do not eat them, the evidence does not justify reintroducing them solely to correct a supposed C15:0 deficiency.
To identify foods that provide fiber without confusing soluble with fermentable, use the table of soluble and insoluble fiber · FR. Their dietary value does not depend on buying a C15:0 test.
Does a supplement being sold in France mean it has been validated?
No. The Ministry of Agriculture distinguishes foods from medicines and points out that a notification does not guarantee every product’s compliance. This general framework does not allow us to certify the regulatory status of any particular C15:0 product here. A US opinion on a food use does not constitute European authorization to treat a disease.
Before considering a product with a healthcare professional, ask for its exact identity, the amount of C15:0 per dose, batch traceability and purity and contaminant analyses. A store’s star rating measures none of these things. With no established clinical benefit in healthy adults, I see no reason to pay to increase a blood marker.
