Protocols by Charles Sieg

Supplements

fatty15 (C15:0)

What the research says about C15:0, the odd-chain fatty acid in fatty15, how much of that research the company behind it wrote or paid for, and what the first human trials show.

Overall evidence Early16 sourcesReviewed November 5, 2026

Observational studies link higher blood C15:0 to less type 2 diabetes, but only two small 12-week randomized trials have given people C15:0, one of them mainly a diet trial, and much of the lab research comes from the company's co-founders.

The short version

  • I take fatty15 from Seraphina Therapeutics. It is pentadecanoic acid, or C15:0, an odd-chain saturated fatty acid found in trace amounts in dairy fat and some fish and plants1.
  • In observational studies, people with more C15:0 in their blood got type 2 diabetes less often (a hazard ratio of 0.80 across 16 pooled cohorts)2. The same kind of data shows no link with cardiovascular disease overall3, and a 2026 study found no link with new cardiovascular disease and no genetic evidence that C15:0 itself lowers blood pressure4.
  • Only two randomized trials have given people C15:0, both for 12 weeks. One had 30 young adults and mainly showed that the capsules raise blood levels5. The other had 88 women and paired C15:0 with a diet change, and the diet did most of the work6.
  • The idea that C15:0 is an "essential" fatty acid comes from a 2020 paper led by a Seraphina co-founder, and two companies she co-founded, Seraphina and Epitracker, financed those studies1. Seraphina also supplied the capsules and placebo for the 30-person trial5.
  • I'd call it promising and unproven, not settled.

The protocol

This is what the maker's pages and the trials describe. It is not a prescription, and my own dose and timing aren't listed here.

ParameterWhat the sources say
FormOriginal Capsules hold 100 mg of C15:0 each, with no fillers or oil; the adult gummies hold 50 mg per gummy7
What the maker suggestsStart with 1 or 2 capsules a day, with or without food7. The FAQ recommends starting with 1 capsule a day, says some customers take 2, and cites safety studies up to 250 mg8
What the trials used200 mg a day for 12 weeks in the supplement-only trial5. A registered trial in adults 55 and older plans 200 mg and 300 mg a day against placebo for about 12 weeks9
Blood levelIn the 12-week trial, blood C15:0 rose 1.88 µg/mL more on C15:0 than on placebo, and half the C15:0 group ended above 5 µg/mL5
Longest human data12 weeks, in both completed trials5,6. I found nothing longer in people

How I use it

I take fatty15 from Seraphina Therapeutics. The company sells capsules and gummies10, and I haven't said here which one I take, how much, or when.

Why it works

The proposal is that C15:0 is a nutrient the body needs but doesn't readily make, so a diet low in it could leave the body worse off. That idea comes from a 2020 paper in which C15:0 eased inflammation, anemia, dyslipidemia, and fibrosis in animals; its lead author co-founded Seraphina, and Seraphina and Epitracker financed the studies1. It's a hypothesis, not an established fact.

The rest of the support is lab work. Across 12 human cell systems, pure C15:0 wasn't toxic to cells at any concentration tested, while EPA, an omega-3, was toxic to four systems at the highest one11. In another cell study, C15:0 and the drug rapamycin shared 24 activities at their best doses12. Seraphina co-founder Stephanie Venn-Watson led both11,12. Separately, a 2026 Nature paper from a group with no stated tie to Seraphina found that C15:0 cut artery plaque by around 50% in mice and directly blocked HMG-CoA reductase, the enzyme statins target; one of its authors is an inventor on a pending patent application for using C15:0 against atherosclerosis13. None of this tells me what a capsule does in a person.

What the research says

Early Does the supplement raise blood C15:0? Yes. In a double-blind trial of 30 young adults with overweight or obesity (20 on C15:0, 10 on placebo), 200 mg a day for 12 weeks raised blood C15:0 by 1.88 µg/mL more than placebo (P = 0.003), with no significant adverse events5. Half the C15:0 group ended above 5 µg/mL, and in that half the liver enzyme ALT fell more (−29 U/L, P = 0.001) and hemoglobin rose more (0.60 g/dL, P = 0.010) than in participants who didn't reach that level5. That was an exploratory comparison that sorts people by the level they reached, not by random assignment, so it's a lead, not proof. The NIH partly funded the trial, and Seraphina supported it and supplied the C15:0 and the matching placebo5.

Early Liver fat and cholesterol. The TANGO trial assigned 88 Chinese women with fatty liver disease to an Asian-adapted Mediterranean diet with C15:0 (31), the same diet without it (28), or their usual diet (29) for 12 weeks. Weight fell 4.0, 3.4, and 1.5 kg and liver fat fell 33%, 30%, and 10%, so the diet did most of the work. C15:0 lowered LDL cholesterol further and raised a gut bacterium, Bifidobacterium adolescentis6. The abstract gives no number for the LDL change, so I can't say how big it was. The authors report no conflicts of interest, and the record I read doesn't say who supplied the C15:06.

Mixed Blood C15:0 and disease in large observational studies. Pooling 16 prospective cohorts (63,682 people, 15,180 new cases of type 2 diabetes, about 9 years of follow-up), higher 15:0 levels went with less diabetes (HR 0.80, 95% CI 0.73 to 0.87, comparing the 90th with the 10th percentile), as did 17:0 (0.65) and trans-palmitoleic acid (0.82)2. For the heart it's weaker: a meta-analysis of 13 studies (7,680 cases) found no link between 15:0 and cardiovascular disease overall (RR 0.94, 95% CI 0.77 to 1.15), though a subgroup analysis found less heart failure (RR 0.72, 95% CI 0.55 to 0.95)3. In 3,196 adults in CARDIA, replicated in 3,889 in ARIC, higher C15:0 went with lower blood pressure and less new hypertension (HR 0.86 per SD) but not with new cardiovascular disease, and a Mendelian randomization analysis found no evidence that C15:0 causes the blood pressure difference4. All of this is observational.

Early C15:0 isn't a clean marker of dairy fat. In a 12-week diet trial of 62 people eating dairy-limited, low-fat dairy, or full-fat dairy diets, blood C15:0 and C17:0 didn't track dairy fat intake once liver fat was accounted for14. That matters because the large studies above use these fatty acids as markers of dairy fat2,3. Whether a purified capsule acts like the C15:0 that comes with food is a separate, open question.

Early Cells and mice. See "Why it works" above. None of that work measured a health outcome in people11,12,13.

What's still unknown: the only registered trial I found in older adults, with a red blood cell measure (red cell distribution width) as its main outcome, was not yet recruiting as of its October 5, 2026 update, and its sponsor is a company, ReCellience15, Inc.9. I found no trial that has tested fatty15 against heart attacks, diabetes, or any other disease endpoint.

Rhonda Patrick on C15:0

Rhonda Patrick took a listener question, "Does pentadecanoic acid offer any health benefits?", at 00:24:43 of FoundMyFitness Q&A #64, a members-only episode posted November 2, 202415. The show notes link three papers for it: the 12-week supplement trial, the TANGO trial, and the 2022 cell study15. The public page has no transcript, so I couldn't read her answer and I'm not attributing a view to her. Her taking the question doesn't mean she endorses me, this supplement, or this site.

About Seraphina Therapeutics

Seraphina, based in San Diego, was co-founded by Stephanie Venn-Watson, a veterinary epidemiologist whose Navy dolphin research led to its C15:0 work, and Eric Venn-Watson, a physician and Navy veteran16,7. Seraphina and Epitracker financed the 2020 studies she led that proposed C15:0 as essential, and Seraphina supplied the capsules for the 30-person trial1,5. The full profile, including its quality claims, is on the companies page.

Where I buy it

Prices aren't listed because they change.

Cautions

  • The FDA doesn't approve dietary supplements, and fatty15's pages carry the standard statement that its claims haven't been evaluated by the FDA8,10.
  • The longest human data run 12 weeks, so long-term safety isn't established5,6.
  • The FAQ says customers may take fatty15 instead of fish oil, citing the company's own cell study, while telling customers to keep taking any omega-3 their doctor prescribed8. That swap rests on cells in a dish, not a trial in people11.
  • The 5 µg/mL finding is an exploratory comparison inside one small trial, not a target to chase5.
  • More C15:0 in the blood isn't the same as taking a capsule: the cohort data are observational, and the genetic analysis in the 2026 study found no causal effect on blood pressure4.
  • The FAQ encourages talking with a healthcare provider before starting any supplement8.

References

  1. Venn-Watson S, Lumpkin R, Dennis EA. Efficacy of dietary odd-chain saturated fatty acid pentadecanoic acid parallels broad associated health benefits in humans: could it be essential?. Scientific Reports. 2020;10(1):8161.Lab or mechanistic studyPubMed 32424181 · DOI

    What it found: Research paper proposing C15:0, an odd-chain saturated fatty acid present in trace levels in dairy fat and some fish and plants, as a potential essential fatty acid: in animal studies C15:0 attenuated inflammation, anemia, dyslipidemia, and fibrosis, and the authors pair this with evidence that C15:0 is not readily made in the body and that lower intake and blood levels are associated with higher mortality.

    Limits: Animal and cell work plus a hypothesis, not a trial of the supplement; the lead author co-founded and works for Seraphina Therapeutics and Epitracker, which the paper's competing-interest statement says financed the studies and hold exclusive licensing rights from the U.S. Navy.

  2. Imamura F, Fretts A, Marklund M, Ardisson Korat AV, Yang WS, Lankinen M, et al. Fatty acid biomarkers of dairy fat consumption and incidence of type 2 diabetes: A pooled analysis of prospective cohort studies. PLoS Medicine. 2018;15(10):e1002670.Cohort studyPubMed 30303968 · DOI

    What it found: Pooled analysis of 16 prospective cohorts from 12 countries (63,682 participants, 15,180 new type 2 diabetes cases, about 9 years of follow-up): higher circulating or adipose-tissue 15:0 went with lower diabetes risk (HR 0.80, 95% CI 0.73 to 0.87, per 10th to 90th percentile range), as did 17:0 (0.65) and trans-palmitoleic acid (0.82).

    Limits: Observational, the markers cannot tell milk from cheese or yogurt, residual confounding is possible, and several authors report ties to Unilever and dairy industry associations.

  3. Liang J, Zhou Q, Kwame Amakye W, Su Y, Zhang Z. Biomarkers of dairy fat intake and risk of cardiovascular disease: A systematic review and meta analysis of prospective studies. Critical Reviews in Food Science and Nutrition. 2018;58(7):1122-1130.Meta-analysisPubMed 28001085 · DOI

    What it found: Meta-analysis of 13 prospective studies with 7,680 cardiovascular disease cases: comparing the top with the bottom third of blood levels, 15:0 was not linked to cardiovascular disease overall (RR 0.94, 95% CI 0.77 to 1.15), though a subgroup analysis linked it to less heart failure (RR 0.72, 0.55 to 0.95), and 17:0 was linked to less disease (RR 0.82, 0.68 to 0.99).

    Limits: Pooled observational cohorts using blood markers of dairy fat, so it cannot show that raising C15:0 with a supplement would change risk.

  4. Steffen BT, Jacobs DR, Li A, Tang W, Duprez D, Mathew M, et al. Plasma pentadecanoic acid is modestly related to cardiovascular health in CARDIA and ARIC cohorts: observational associations without evidence of causality. Frontiers in Nutrition. 2026;13:1720975.Cohort studyPubMed 41743064 · DOI

    What it found: Cohort analysis of 3,196 CARDIA participants, replicated in 3,889 ARIC participants: higher plasma C15:0 went with lower blood pressure and lower 10-year hypertension risk (HR 0.86 per SD) but not with incident cardiovascular disease or echocardiographic measures, and two-sample Mendelian randomization found no evidence of a causal effect on blood pressure, resting heart rate, or hypertension.

    Limits: Observational, measuring blood C15:0 from diet and metabolism rather than a supplement, and the authors conclude the evidence does not support a causal cardiovascular benefit.

  5. Robinson MK, Lee E, Ugalde-Nicalo PA, Skonieczny JW, Chun LF, Newton KP, et al. Pentadecanoic Acid Supplementation in Young Adults with Overweight and Obesity: A Randomized Controlled Trial. The Journal of Nutrition. 2024;154(9):2763-2771.Randomized trialPubMed 39069269 · DOI

    What it found: Double-blind randomized trial of 200 mg/day of C15:0 versus placebo for 12 weeks in 30 young adults with overweight or obesity (20 on C15:0, 10 on placebo). Blood C15:0 rose 1.88 µg/mL more on C15:0 (P = 0.003) with no significant adverse events; in the half who reached a level above 5 µg/mL, ALT fell more (-29 U/L, P = 0.001) and hemoglobin rose more (0.60 g/dL, P = 0.010) than in those who did not.

    Limits: Thirty people for 12 weeks; the main result is only that the supplement raised blood C15:0, the liver-enzyme and hemoglobin findings come from an exploratory comparison by the level people reached, and Seraphina Therapeutics, which sells fatty15, supported the trial and supplied the C15:0 and matching placebo (full text, Funding section), alongside an NIH grant.

  6. Chooi YC, Zhang QA, Magkos F, Ng M, Michael N, Wu X, et al. Effect of an Asian-adapted Mediterranean diet and pentadecanoic acid on fatty liver disease: the TANGO randomized controlled trial. The American Journal of Clinical Nutrition. 2024;119(3):788-799.Randomized trialPubMed 38035997 · DOI

    What it found: Double-blind trial of 88 Chinese women with fatty liver disease for 12 weeks: an Asian-adapted Mediterranean diet with C15:0 (31), the same diet without C15:0 (28), or habitual diet (29). Weight fell 4.0, 3.4, and 1.5 kg and liver fat fell 33%, 30%, and 10%; C15:0 added a further LDL-cholesterol reduction and raised Bifidobacterium adolescentis.

    Limits: The diet, not C15:0, drove most of the benefit, the abstract gives no numbers for the LDL change, the record does not say who supplied the C15:0, and it is 12 weeks in women of one ethnic group.

  7. Seraphina Therapeutics. Fatty15 Ingredients: A Full Breakdown of What's Inside. fatty15 (Seraphina Therapeutics), October 27, 2026.Product pageRead

    What it found: The maker's own ingredients post: each Original Capsule has 100 mg of C15:0 and nothing else (no fillers or oil), the company recommends starting with 1 or 2 capsules a day, adult gummies have 50 mg per gummy at 2 to 4 gummies a day, kids gummies have 25 mg per gummy, each batch is tested to confirm 98% or higher purity, and the page names Stephanie Venn-Watson and Eric Venn-Watson as co-founders.

    Limits: Company marketing copy, so the purity and third-party testing statements are the seller's own and I did not see a certificate; the page does not name who manufactures the C15:0.

  8. Seraphina Therapeutics. FAQs. fatty15 (Seraphina Therapeutics), 2026.Product pageRead

    What it found: The maker's FAQ says fatty15 is sold on its own website and on Amazon, that the FA15 ingredient is tested for 98% or higher purity and made under cGMP, that the recommended starting dose is one capsule a day (some customers take two, and it cites safety studies up to 250 mg), that customers may use it in place of fish oil but keep any omega-3 a doctor prescribed, and that FDA does not approve dietary supplements.

    Limits: Company statements; the page is undated, and its GRAS and testing claims are the seller's own, not checked against a regulator or certifier.

  9. ReCellience15, Inc. Effect of Pentadecanoic Acid Supplementation on Red Blood Cell Health and Biological Aging in Healthy Older Adults. ClinicalTrials.gov (NCT07812792), October 5, 2026.ArticleRead

    What it found: Registry record, not yet recruiting as of its October 5, 2026 update: a planned placebo-controlled trial of 93 adults aged 55 and older, randomized 1:1:1 to C15:0 at 200 mg/day, 300 mg/day, or placebo for about 12 weeks, with change in red cell distribution width as the primary outcome and a start date of January 2027.

    Limits: A plan, not a result; the sponsor is an industry company (ReCellience15, Inc, with Nutrasource as collaborator), and the registry says nothing about whether the trial will find anything.

  10. Seraphina Therapeutics. fatty15 Starter Kit 90-day Supply MHS. fatty15 (Seraphina Therapeutics), 2026.Product pageRead

    What it found: A fatty15 product page that links the company's lines: Original Capsules, Gummies for Adults, Gummies for Kids, a practitioner-only Advanced Formula sold through approved healthcare practitioners and Fullscript, and a book; it carries the standard statement that the claims have not been evaluated by the FDA.

    Limits: The supplement facts on this page are an image I could not read, and the page is undated.

  11. Venn-Watson SK, Butterworth CN. Broader and safer clinically-relevant activities of pentadecanoic acid compared to omega-3: Evaluation of an emerging essential fatty acid across twelve primary human cell-based disease systems. PLoS One. 2022;17(5):e0268778.Lab or mechanistic studyPubMed 35617322 · DOI

    What it found: Cell-based screen of pure C15:0 at four concentrations against EPA across 12 primary human cell systems and 148 biomarkers: C15:0 was not cytotoxic at any tested dose, while EPA was cytotoxic in four systems at the highest dose.

    Limits: Cells in a dish, not people; the work was funded by an Office of Naval Research award to Epitracker, the lead author is paid by Epitracker and Seraphina Therapeutics, and the authors disclose patents owned by the U.S. Navy or Epitracker and licensed to Seraphina, which sells a C15:0 product.

  12. Venn-Watson S, Schork NJ. Pentadecanoic Acid (C15:0), an Essential Fatty Acid, Shares Clinically Relevant Cell-Based Activities with Leading Longevity-Enhancing Compounds. Nutrients. 2023;15(21):4607.Lab or mechanistic studyPubMed 37960259 · DOI

    What it found: Cell-based comparison of C15:0 with acarbose, metformin, and rapamycin: C15:0 and rapamycin had the most dose-dependent activities, and the two shared 24 activities at their optimal doses, including anti-inflammatory and anticancer effects.

    Limits: Cell-based, so it says nothing about clinical outcomes, and the authors are co-founders of Seraphina Therapeutics (Venn-Watson is also employed there; Schork consults for it), which sells fatty15.

  13. Yin C, Chen Y, Lin G, Cai M, Pang C, Xiao X, et al. A gut microbial odd-chain fatty acid alleviates atherosclerosis in mice. Nature. 2026.Lab or mechanistic studyPubMed 42844473 · DOI

    What it found: Mouse atherosclerosis study of pentadecanoic acid (C15:0): supplementation reduced plaque burden by around 50%, and the authors' mechanistic work found it inhibits HMG-CoA reductase and lowers hepatic cholesterol synthesis; patients with dyslipidemia were reported to be markedly depleted in it.

    Limits: Mostly mice with no human trial, published ahead of print as of the record I opened, and one author is an inventor on a pending patent application for its use against atherosclerosis.

  14. Bethancourt HJ, Schmidt KA, Cromer G, Burhans MS, Kuzma JN, Hagman DK, et al. Assessing the validity of plasma phospholipid fatty acids as biomarkers of dairy fat intake using data from a randomized controlled intervention trial. The American Journal of Clinical Nutrition. 2022;115(6):1577-1588.Randomized trialPubMed 35134818 · DOI

    What it found: Secondary analysis of a 12-week randomized diet trial of 62 people given a dairy-limited (0.3 g/day dairy fat), low-fat dairy (8.7 g/day), or full-fat dairy (28.5 g/day) diet: trans-C16:1n-7 plus iso-C17:0 explained 35.4% of the variation in dairy fat intake, while C15:0 and C17:0 were not associated with dairy fat intake after adjusting for liver fat.

    Limits: A secondary analysis of one small diet trial that tests whether blood C15:0 is a good marker of dairy fat, not any health outcome.

  15. Patrick R. Q&A #64: Peptide Therapies—BPC-157, TB-500, & GHK-Cu. FoundMyFitness, November 2, 2024.PodcastListen

    What it found: Rhonda Patrick's members-only Q&A episode; its show notes list a listener question at 00:24:43, "Does pentadecanoic acid offer any health benefits?", with links to the Robinson 2024 trial, the TANGO trial, and the 2022 Venn-Watson cell study, but give no answer and the page has no transcript.

    Limits: I could confirm only that she took the question; I could not read what she said, so nothing here is her view of C15:0.

  16. Daniells S. Fatty15: New supplement brand brings good saturated fat from US Navy dolphins to consumers. NutraIngredients, November 19, 2020.ArticleRead

    What it found: Trade profile of the launch of fatty15 as a San Diego-based brand led by Stephanie Venn-Watson, whose Navy dolphin health research led to the company's C15:0 work.

    Limits: A launch-era trade article that does not give the company's founding year, its other founders, or any license terms with the Navy.