What is C15 Fatty Acid?

Original Date of Publication: November 13, 2024

Original Author: Judy Blatman is OmegaQuant’s consumer health writer. Her blogs tee-up practical suggestions for health, with an emphasis on omega-3s and omega-3 testing, so readers can decide their own path to good health. Judy’s knowledge about dietary supplements developed during her 16 years spearheading communications for the Council for Responsible Nutrition, where she led an award-winning healthy lifestyle consumer education initiative focused on diet, dietary supplements and exercise. Learn more 

Date of Review/Update: June 22, 2026

Reviewer: Stacy Cappadona MS, RD, CSSD, CSCS, TSAC-F

Stacy Cappadona is OmegaQuant’s science writer and reviewer. She is a registered dietitian and board-certified specialist in sports dietetics. Stacy has spent most of her career supporting the health and performance of United States military communities, applying evidence-based nutrition strategies to meet the demands of high-stress, high-performance environments. Learn more

 

Key Points:

• C15 is a saturated fat found mainly in dairy products.
• Some studies link higher C15 levels to better health, including lower risks of diabetes and heart disease.
• Most evidence is observational, so it doesn’t prove C15 causes these benefits.
• More human research is needed before C15 supplements can be recommended.

 

You may have seen some sexy headlines touting a nutrient you might not have heard of, accompanied by health claims that make you want to know more. The nutrient is C15, and the claims suggest it can “reverse cellular aging,” “lower the risk of obesity and early death,” and “enhance longevity.” One article even called it a “do-it-all nutrient.”

Sounds great, right? Well, you know the saying: if it sounds too good to be true, it probably is.

That’s not to say C15 doesn’t have health benefits. It’s simply to say that these claims are lofty and, at this point, more likely to be marketing hype than to be scientifically supported. Let’s start with the basics.

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What is C15 and What Does it Do?

Fatty acids perform various functions that depend on their characteristics, such as the length of their carbon chain, their level of saturation, and the location and number of double bonds (1). There are 3 primary types of dietary fats: trans-fat, unsaturated fat, and saturated fat.

• Trans fats, also known as “partially hydrogenated” fats, are the worst type of fat for you and have negative effects on your health (2). We won’t spend too much time on trans fats here because they were found to be so harmful that a series of policy initiatives led to their near elimination from the U.S. food supply by 2018. If you’re reading this from outside the United States, though, keep your eyes peeled. Trans fats are most commonly found in fried, baked, or highly processed snack foods, as well as in margarine.
• Unsaturated fats, on the other hand, are known as the “good” or “healthy” fats. These fats contain at least one double bond and are associated with health benefits, including improved cardiovascular health (3), reduced inflammation (4), and improved brain function (5). There are two primary types of unsaturated fats: monounsaturated and polyunsaturated. These fats are found in high amounts in plant sources such as vegetable oils, nuts, seeds, and avocados, as well as in The well-known omega-3 fats, EPA and DHA, are polyunsaturated fats.
• Saturated fats have no double bonds, so they are “saturated” with hydrogens. Their effects on health fall somewhere in the middle—not as “good” as unsaturated fats, but not as “bad” as trans fats. For this reason, experts recommend limiting saturated fat intake to less than 10% of your daily calories (6). In the U.S., the biggest sources of saturated fat come from pizza, cheese, whole-fat dairy, meat products (sausage, bacon, beef), cookies and other desserts, and fast food (2).

Although the general message from the scientific community still seems to be that cutting back on saturated fat can be good for health if you replace it with unsaturated fats, there has been some debate on this topic. Like unsaturated fats, saturated fats come in different forms, and the argument is that while some may be harmful, others may be helpful.

C15:0, also known as pentadecanoic acid (PDA), is a 15-carbon saturated fatty acid (hence the number 15 in the name) with zero double bonds (and the number 0) (7). Also referred to as an “odd-chain fatty acid,” it’s a major source of odd-chain fatty acids in cow’s (and other bovine) milk, followed closely by C17:0, or heptadecanoic acid (HDA) (7).

PDA is a byproduct of bacterial fiber fermentation in the cow’s rumen—the first large compartment of the animal’s multi-chambered stomach (7). While bovine milk seems to be the richest source of C15 fats, they have also been found in lesser amounts in meat and fish products (7).

Some have called C15 an “essential” fat, meaning our bodies don’t produce it on their own. In other words, the only way to get C15 fatty acids is through the foods we eat. However, there is a second criterion for being labeled “essential,” and that is that it’s required to maintain a healthy physiological state—and this is where the controversy lies. To hear more about this conversation, you can watch our video podcast. Or keep reading. Or both!

VIDEO: C15, A-Fib and More: Ask Us Anything Part 1

 

What is the State of the Science for C15 benefits?

So, this is where things get a little dicey. First, some argue that the health benefits associated with dairy, such as a decreased risk of type 2 diabetes (8) and non-alcoholic fatty liver disease (9), could be due to increased intake of C15. While this may be true, dairy products also contain other nutrients (such as vitamin D, calcium, protein, and more) that provide health benefits. So, there is no way to tell whether C15 is the nutrient responsible for the improved health outcomes observed in dairy studies.

Next, there are relatively few human studies investigating this nutrient. While studies in cell cultures and animals are valuable for advancing nutrition research, their findings need to be confirmed in humans before we know whether they apply to people. You can’t simply generalize findings from animal and cell culture studies, assuming they apply to living, breathing humans.

Finally, most human studies report associations or correlations with health—not causation—particularly regarding type 2 diabetes and metabolic syndrome. Association (correlation) means that two things tend to occur together. Causation means that one thing directly causes the other to happen.

A clear example illustrating the difference is comparing ice cream sales rates and shark bite rates. Let’s say that as ice cream sales go up, so do shark bites. Does this mean that ice cream sales are causing the shark bites? No. This example demonstrates correlation (both ice cream sales and shark bite rates tend to rise together, probably because it’s summertime and more people are swimming and buying ice cream) but not causation (ice cream intake is not the cause of shark bites).

A 2026 systematic review and meta-analysis of 44 observational studies compared circulating fatty acid profiles in pregnant women with and without gestational diabetes and examined associations between these profiles and the risk of gestational diabetes (10). Regarding C15:0, the researchers found that women with gestational diabetes had lower levels of C15:0 and C17:0 than the control group (10). While this is an interesting finding that warrants future research into this correlation, it does not allow us to conclude that low levels of these odd-chain saturated fats cause this condition.

Similarly, a 2025 cross-sectional study investigated the association between serum levels of odd-chain fatty acids (C15:0 and C17:0) and hypertension (11). They found that both serum C15:0 and C17:0 were inversely associated with the odds of hypertension. Several earlier studies also show associations between PDA (C15:0) levels and health outcomes, including the risk of type 2 diabetes, certain liver diseases, cardiovascular risk, and inflammation (12, 13, 14, 15, 16,17).

Another 2025 analysis examined the association of circulating saturated and unsaturated fatty acids with incident cardiovascular disease (CVD) outcomes. The researchers found that higher concentrations of total saturated fatty acids were associated with increased cardiovascular risk, but the relationships between saturated fats and CVD varied by subtype. Interestingly, they observed that higher levels of even-chain saturated fatty acids were associated with a higher risk, whereas higher levels of odd-chain fatty acids were associated with a lower risk. However, these are associations, and no causal relationship can be determined from this evidence (7).

Still, very few human studies have been conducted that suggest causality. One randomized trial showed that 200 mg/d of C15:0 supplementation increased plasma levels in overweight and obese adults with “potentially relevant” effects on liver function and red blood cell health (18).

Another study examined the effects of a reduced-calorie, Mediterranean-like, culturally contextualized Asian diet, with or without C15:0 supplementation, in Chinese females with nonalcoholic fatty liver disease (19). This was a double-blind, parallel-design, randomized controlled trial.

Eighty-eight participants were assigned to 1 of 3 groups for 12 weeks: diet with C15:0 supplementation, diet without C15:0 supplementation, or a control group (habitual diet with no supplementation). The researchers reported that although all groups achieved reductions in body weight and liver fat, C15:0 supplementation led to further reductions in LDL-cholesterol compared with no supplementation (19). Furthermore, they found that C15:0 supplementation increased beneficial bacteria in the gut (19).

This is one of the only studies to date showing that C15:0 intake can independently provide health benefits, lowering LDL cholesterol and improving the gut microbiome. However, it’s important to note that while this is promising evidence, the study population was small (only 31 participants were included in the C15:0 supplement group) and limited to Asian females with nonalcoholic fatty liver disease. So, before you run to the store to buy a C15 supplement to lower your cholesterol, more research is needed to confirm these findings in other populations.

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Bottomline

In short, the scientific evidence that C15 is independently beneficial for human health is limited.

Does C15:0 challenge the traditional categorization that all saturated fats are harmful? Yes.

Is C15:0 a “good” saturated fatty acid? It’s too soon to say.

While there are associations between C15:0 levels and positive health outcomes, more research is needed to understand the health effects of different saturated fat subtypes, including randomized clinical trials to distinguish causation from correlation.

So, don’t go out and buy any C15:0 supplements just yet. Instead, focus on a well-rounded diet rich in fruits, vegetables, lean proteins, and fiber. Choose unsaturated fats over saturated fats and prioritize whole foods over single nutrients or supplements. In the meantime, continue to watch as evidence in this field grows.

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References:

 

1. Retterstøl K, Rosqvist F. Fat and fatty acids – a scoping review for Nordic Nutrition Recommendations 2023. Food Nutr Res. 2024;68:10.29219/fnr.v68.9980. Published 2024 Jan 12. doi:10.29219/fnr.v68.9980
2. Harvard T.H. Chan School of Public Health. Types of fat. The Nutrition Source. Accessed June 20, 2026.https://nutritionsource.hsph.harvard.edu/what-should-you-eat/fats-and-cholesterol/types-of-fat/
3. Lichtenstein AH, Khera A, Anderson CAM, et al. 2026 Dietary Guidance to Improve Cardiovascular Health: A Scientific Statement From the American Heart Association.Circulation. Published online March 31, 2026. doi:10.1161/CIR.0000000000001435
4. Coniglio S, Shumskaya M, Vassiliou E. Unsaturated Fatty Acids and Their Immunomodulatory Properties.Biology (Basel). 2023;12(2):279. Published 2023 Feb 9. doi:10.3390/biology12020279
5. von Schacky C. Importance of EPA and DHA Blood Levels in Brain Structure and Function.Nutrients. 2021;13(4):1074. Published 2021 Mar 25. doi:10.3390/nu13041074
6. U.S. Department of Health and Human Services; U.S. Department of Agriculture.Dietary Guidelines for Americans, 2025–2030. January 2026. Accessed June 20, 2026.https://cdn.realfood.gov/DGA.pdf
7. Ciesielski V, Legrand P, Blat S, Rioux V. New insights on pentadecanoic acid with special focus on its controversial essentiality: a mini-review.Biochimie. 2024;227(Pt B):123-129. doi:10.1016/j.biochi.2024.10.008
8. Aune D, Norat T, Romundstad P, Vatten LJ. Dairy products and the risk of type 2 diabetes: a systematic review and dose-response meta-analysis of cohort studies.Am J Clin Nutr. 2013;98(4):1066-1083. doi:10.3945/ajcn.113.059030
9. Yuzbashian E, Fernando DN, Pakseresht M, Eurich DT, Chan CB. Dairy product consumption and risk of non-alcoholic fatty liver disease: A systematic review and meta-analysis of observational studies.Nutr Metab Cardiovasc Dis. 2023;33(8):1461-1471. doi:10.1016/j.numecd.2023.04.018
10. Shojaei-Zarghani S, Naziri Z, Nasr M, Rostamian F, Mokhtari Z, Kazemi A. Circulating fatty acids and gestational diabetes mellitus: A systematic review and meta-analysis of observational studies. Diabetes Metab Syndr. 2026;20(3):103398. doi:10.1016/j.dsx.2026.103398
11. Chen T, Luo J, Li S, et al. Associations between serum pentadecanoic acid (C15:0) and heptadecanoic acid (C17:0) levels and hypertension: a cross-sectional analysis of NHANES data. Lipids Health Dis. 2025;24(1):219. Published 2025 Jun 20. doi:10.1186/s12944-025-02640-4
12. Forouhi NG, Koulman A, Sharp SJ, et al. Differences in the prospective association between individual plasma phospholipid saturated fatty acids and incident type 2 diabetes: the EPIC-InterAct case-cohort study. Lancet Diabetes Endocrinol. 2014;2(10):810-818. doi:10.1016/S2213-8587(14)70146-9
13. Imamura F, Fretts A, Marklund M, et al. Fatty acid biomarkers of dairy fat consumption and incidence of type 2 diabetes: A pooled analysis of prospective cohort studies. PLoS Med. 2018;15(10):e1002670. Published 2018 Oct 10. doi:10.1371/journal.pmed.1002670
14. Santaren ID, Watkins SM, Liese AD, et al. Individual serum saturated fatty acids and markers of chronic subclinical inflammation: the Insulin Resistance Atherosclerosis Study. J Lipid Res. 2017;58(11):2171-2179. doi:10.1194/jlr.P076836
15. Yoo W, Gjuka D, Stevenson HL, et al. Fatty acids in non-alcoholic steatohepatitis: Focus on pentadecanoic acid. PLoS One. 2017;12(12):e0189965. Published 2017 Dec 15. doi:10.1371/journal.pone.0189965
16. Kurotani K, Sato M, Yasuda K, et al. Even- and odd-chain saturated fatty acids in serum phospholipids are differentially associated with adipokines. PLoS One. 2017;12(5):e0178192. Published 2017 May 26. doi:10.1371/journal.pone.0178192
17. Shi F, Chowdhury R, Sofianopoulou E, et al. Association of circulating fatty acids with cardiovascular disease risk: analysis of individual-level data in three large prospective cohorts and updated meta-analysis. Eur J Prev Cardiol. 2025;32(3):233-246. doi:10.1093/eurjpc/zwae315
18. Robinson MK, Lee E, Ugalde-Nicalo PA, et al. Pentadecanoic Acid Supplementation in Young Adults with Overweight and Obesity: A Randomized Controlled Trial. J Nutr. 2024;154(9):2763-2771. doi:10.1016/j.tjnut.2024.07.030
19. Chooi YC, Zhang QA, Magkos F, et al. Effect of an Asian-adapted Mediterranean diet and pentadecanoic acid on fatty liver disease: the TANGO randomized controlled trial. Am J Clin Nutr. 2024;119(3):788-799. doi:10.1016/j.ajcnut.2023.11.013