Pentadecylic acid

Pentadecanoic acid (C15:0, also called pentadecylic acid; C15H30O2) is a saturated fat. It has 15 carbons in a straight chain. The common saturated fats in the FAO and WHO list all have an even number of carbons, so an odd count makes this one unusual. FAO and WHO (the UN food and health agencies) class fatty acids with 14 to 20 carbons as long-chain.

It is a minor fat. A review puts the two main odd-chain fatty acids together at only 1.5% to 2.5% of milk fat. They are C15:0 and margaric acid (heptadecanoic acid, C17:0). It is a close neighbor of palmitic acid (C16:0), but a different molecule with a different story.

Its main source is the stomach of ruminant animals such as cows. Microbes in the rumen make odd-chain fatty acids, and these pass into milk fat and meat. So blood C15:0 has long served as a marker of how much dairy fat a person eats.

It is a leaky marker. People make some C15:0 themselves. In a trial in 16 healthy adults, a week of inulin, a fiber, raised blood C15:0 by about 17%.

The health story is why people search for it. In large cohort studies (studies that follow big groups of people over time), people with higher blood C15:0 had less type 2 diabetes. They had less heart disease in some studies but not in others. One 2026 analysis using genetic data found no sign that C15:0 causes a change in blood pressure.

Researchers at Seraphina Therapeutics, which sells a C15:0 supplement, proposed in 2020 that it is an essential fatty acid. FAO and WHO name only linoleic acid and alpha-linolenic acid as indispensable. We found no C15:0 claim in the EU Register of nutrition and health claims. Two small randomized trials of C15:0 have been published.

Health benefits of pentadecanoic acid (C15:0)

• ★C15:0 capsules raised blood C15:0 levelsIn 30 young adults with overweight or obesity, 200 mg a day raised blood C15:0 by 1.88 µg/mL more than placebo over 12 weeks. No significant adverse events occurred, and the maker supplied the capsules.
• ★Dairy and inulin fiber raised blood C15:0In 30 young adults, a dairy-rich diet raised blood C15:0 more than meat or grain diets. In 16 healthy adults, 7 days of inulin fiber raised it by about 17%.
• Population studyLinked to less type 2 diabetesHigher blood C15:0 went with 0.80 times the risk of type 2 diabetes in 16 cohorts (63,682 people), comparing the 90th with the 10th percentile. In EPIC-InterAct, each standard deviation higher gave 0.79 times the risk.
• Population studyLinked to less cardiovascular disease in some studiesIn 4,150 Swedish adults, higher blood C15:0 went with 0.75 times the risk of cardiovascular disease. A pooled analysis of 13 studies found no clear total link (0.94 times) but less heart failure (0.72 times).
• Population studyLinked to slightly lower blood pressureIn 3,196 US adults, each standard deviation higher C15:0 went with a lower top blood pressure number (1.47 mm Hg). A genetic analysis found no evidence that C15:0 causes this.

Foods high in pentadecanoic acid (C15:0)

Fat from ruminant animals is the main food source. In our USDA ranking per serving, ground beef leads with 0.11 g in 4 oz (113 g). Semi-skimmed cow’s milk follows at 0.05 g in a cup (246 g), then farmed Atlantic salmon at 0.04 g in 3 oz (85 g). Shrimp, chia seeds and a chicken drumstick follow at 0.01 g, and one large egg holds 0.004 g.

The order changes with the measure. Per 100 g, ground beef leads with 0.1 g, then salmon with 0.05 g and chia seeds with 0.03 g. Per 100 kcal, milk and ground beef are close at 0.04 g. Vegetables such as cauliflower and zucchini show only traces, 0.002 g and 0.001 g in a cup.

Butter, cheese and yogurt are not in our ranking, so it understates dairy fat. A review reports that odd-chain fatty acids make up 1.5% to 2.5% of milk fat. C15:0 is about twice as abundant as C17:0. By our arithmetic that puts C15:0 at roughly 1% to 1.7% of milk fat.

What the cow eats changes it. In a feeding study of dairy cows, more grass silage in the diet raised milk C15:0 and C17:0. A study of retail whole milk found more odd- and branched-chain fatty acids per serving in organic milk than in conventional milk. But the abstract does not single out C15:0.

Food is not only dairy and beef. In the China Kadoorie Biobank, where people eat little dairy, red cell C15:0 also tracked wheat, coarse grains, fish and seafood. Part of that is the gut route: fiber feeds bacteria that make propionate, which the liver turns into C15:0 (see below).

For scale, a supplement trial used 200 mg a day. That is what about 4 cups of semi-skimmed milk would give at the ranking values. Nearly 2 four-ounce portions of ground beef would give the same (our arithmetic from 0.05 g and 0.11 g).

How pentadecanoic acid (C15:0) works

Most of what is known about what C15:0 does inside the body comes from cells and animals. Much of it comes from authors tied to a C15:0 supplement maker. The solid human findings are about where blood C15:0 comes from and how well it tracks dairy.

This section covers the sources, the fiber route and how loosely blood levels follow dairy. It then covers how it is absorbed, what cell and animal studies suggest, and what has been seen in people.

Ruminant microbes make it, and so can your own body

A review explains how ruminant animals come to carry C15:0. Microbes in the rumen build fatty acids and can make odd-chain ones. They do it from propionate, or by removing the first carbon of palmitic or stearic acid (alpha-oxidation). In some bacteria, odd-chain acids reach up to 40% of the cell’s fatty acids.

The animal takes them up, and the mammary gland puts them into milk fat.

The review reports a C15:0 to C17:0 ratio of about 2 to 1 in ruminant milk fat. In human plasma the ratio is about 1 to 2, the reverse. The review reads this as a sign that people make some odd-chain fat themselves, possibly by the same alpha-oxidation. That second part is a proposal, not a measurement.

A second review says C15:0 and C17:0 can be made from propionic acid produced in the gut.

The company paper that proposes C15:0 as essential says the body does not readily make it. The fiber trial in the next section found that the liver does make some. A mouse study traced a gut bacterium turning inulin into C15:0. How much of a person’s blood C15:0 is homemade, and how much comes from food, has not been settled.

Fiber raises it too

In the randomized crossover trial, inulin (30 g a day) and propionate (6 g a day) raised plasma C15:0 in 7 days. The rises were about 17% and 13%, and cellulose did nothing. Human liver cancer cells grown in propionate also made more odd-chain fatty acids as the dose rose (R² = 0.99), while palmitic acid fell. The authors conclude that propionate from the gut feeds the liver’s production of odd-chain fatty acids.

The picture is not uniform. In 869 Dutch patients after a heart attack, C15:0 tracked dairy intake but not fiber intake, while C17:0 tracked both. Two authors of that study work for Unilever. A third received Unilever support for studies of these fatty acids in populations.

Blood levels follow dairy fat only loosely

Smedman and colleagues studied 62 older men. C15:0 in cholesterol esters rose with the amount of milk-product fat they ate (r = 0.46). A review calls it the first study of this kind.

Later studies found weaker links, as the chart shows. They ranged from 0.52 in fat tissue down to 0.15 for the odd-chain group in a large European cohort. In 1,180 people across seven countries, C15:0 separated low from high eaters of high-fat dairy, but it performed poorly for total dairy.

A controlled feeding trial confirms the direction, since a dairy-rich diet raised C15:0 more than a meat or grain diet.

Still, a blood level of C15:0 reflects dairy fat, fiber, the body’s own production and other habits at once. That is the main limit on every cohort result on this page.

It is absorbed as a free fatty acid, without help from lipase

A test of fat digestion used C15:0 as a control. In this blood test for malabsorption, people take free pentadecanoic acid (2.5 g in one meal). They take it with heptadecanoic acid bound in a triglyceride that needs pancreatic lipase, a fat-digesting enzyme.

When lipase was blocked in healthy adults, absorption of the bound fat fell by 65% to 71%. It was minimal in cystic fibrosis without enzymes. The free C15:0 was absorbed normally, so the bound fat could be compared against it.

A model fitted to the data gave C15:0 bioavailability (how much is absorbed) in cystic fibrosis comparable to healthy people. That held with and without enzymes. In rats, the supplement-maker paper reports that labeled C15:0 was partly lengthened to C17:0.

Reviews also propose that C15:0 can be lengthened into very-long-chain fats in brain lipids. They propose it can also be shortened to propionyl-CoA, which feeds the cell’s energy cycle. Those are ideas, not measured effects in people.

What cell and animal studies suggest

Cell studies from the supplement-maker group report that C15:0 acts on pathways of inflammation, energy sensing and cell growth. These include AMPK and mTOR, at around 17 µM. In a panel of human cell systems, it shares 24 activities with the drug rapamycin. The same group’s papers note patents owned by the US Navy or Epitracker and licensed to Seraphina Therapeutics.

Other groups report that C15:0 made by gut bacteria protected mice against fatty liver disease (NASH). A 2026 Nature paper reports that it cut artery plaque by around 50% in mice by inhibiting a cholesterol-making enzyme. Its authors include an inventor on a pending patent application for C15:0.

Two mouse and rat studies bear on safety. In pregnant mice, a diet with 1% C15:0 caused mild insulin resistance. An algal oil rich in C15:0 and C17:0 caused no harm in rats up to 15% of the diet. Cells and mice differ from people in dose, diet and biology.

What has been seen in people

Two randomized trials have tested C15:0 in people. In the first, 30 young adults took 200 mg a day for 12 weeks, with no significant adverse events. Their blood C15:0 rose by 1.88 µg/mL more than on placebo.

In the second, adding C15:0 to a Mediterranean-style diet lowered LDL cholesterol further than the diet alone in 88 women. But most of the weight and liver-fat change came with the diet itself. Neither trial tested diabetes, heart disease or deaths. The chart puts the trial dose next to food amounts from our USDA ranking.

The cohort links between blood C15:0 and lower diabetes risk are consistent. But the one genetic analysis we found, for blood pressure, gave no sign of a causal effect. Trial evidence on disease outcomes does not exist. The honest summary is that C15:0 is a well-studied marker and a poorly tested nutrient.

How much pentadecanoic acid (C15:0) do you need?

No health body sets a daily amount of pentadecanoic acid. The FDA has set no Daily Value for it and the EU no EU Reference Intake. We found no mention of it in the 2010 FAO and WHO report on fats. That report names only linoleic acid and alpha-linolenic acid as indispensable fatty acids.

The only target we found comes from supplement research. The authors of the 12-week trial chose 200 mg a day to reach a blood level of at least 5 µg/mL. They derived that level from cell and population evidence, and no health body has endorsed it.

For scale, 200 mg is what about 4 cups of semi-skimmed milk give at our USDA ranking values. Nearly 2 four-ounce portions of ground beef give the same (our arithmetic). We found no disease named for a lack of C15:0 and no accepted blood threshold.

The idea of a C15:0 deficiency comes from the supplement-maker authors. They say circulating odd-chain fatty acids have been declining. They suggest that decades of lower intake may add to chronic disease, and no trial has tested that.

Is C15:0 an essential fatty acid?

Not by the usual definition. FAO and WHO call linoleic acid and alpha-linolenic acid indispensable because humans cannot make them, and set requirements for them. The 2020 proposal uses a looser three-part definition. In it, an essential fatty acid is needed for health, is not made at adequate levels in the body, and must come from the diet.

Its authors, tied to the maker of a C15:0 supplement, say C15:0 fits. The evidence does not settle it. The liver makes some C15:0 from fiber-derived propionate. In rats that lacked essential fats, C15:0 raised early growth, which is suggestive but not a deficiency disease.

We found no study in people or animals that withheld C15:0 and produced a deficiency disease. A 2024 mini-review from French researchers calls its essentiality controversial and says more work is needed on both criteria.

Forms of pentadecanoic acid (C15:0): absorption and effects

C15:0 reaches people in several forms. It comes bound in the fat of milk and ruminant meat, and it is made in the body from fiber. It also comes as the pure free fatty acid in capsules, and as an odd-chain food product in one trial. Animal tests used an odd-chain algal oil.

The honest bottom line is that no trial has compared one form with another, or a supplement with dairy fat. What we know about forms comes from single trials. Free C15:0 capsules raise blood C15:0. A dairy-rich diet raises it, and so does fiber.

The studies of key outcomes above used these forms. Free C15:0 capsules (200 mg a day) were tested on blood levels and liver enzymes. An odd-chain food product added to a diet was tested on LDL cholesterol in women with fatty liver. Fiber and propionate were tested on blood levels, and the cohort studies used no form at all, since they measured what the body held.

Claims that a supplement is absorbed better or works better than dairy fat have no trial behind them.

Form	What it is	What studies show	Source
Dairy and ruminant fat	C15:0 bound in milk fat and meat fat, with many other fats	Odd-chain acids are 1.5% to 2.5% of milk fat. A dairy-rich diet raised blood C15:0 in 30 adults. Butter raised LDL cholesterol in a trial, and we found no trial of the C15:0 in dairy fat on its own.	1, 2, 3
Made in the body	Built by the liver from propionate, which gut bacteria make from fiber; alpha-oxidation of palmitic acid is proposed	Inulin raised blood C15:0 by about 17% in a week in 16 adults, and propionate by 13%. The share of homemade versus dietary C15:0 is unsettled.	1, 4
Free C15:0 capsules	The pure free fatty acid, as in the trial that supplied capsules from a supplement maker	200 mg a day raised blood C15:0 by 1.88 µg/mL more than placebo in 30 adults for 12 weeks. A single 2.5 g dose was absorbed with or without lipase in a pilot. No head-to-head trial against dairy or other forms.	5, 6, 7
Odd-chain food product	A food product containing odd-chain fatty acids, added to a diet	Lowered LDL cholesterol further than the diet alone in 88 women. The abstract gives no dose, and the registry calls the item an odd-chain fatty acid food product.	8, 9
Odd-chain algal oil	A microalgal oil made mostly of C15:0 and C17:0	No adverse effects in rats up to 15% of the diet over 13 weeks. We found no human trial. The authors are at Burdock Group Consultants and Heliae Development.	10

Here are the form-specific studies, strongest evidence first, 3 in all.

Is pentadecanoic acid (C15:0) safe? Supplements, dose and interactions

At the amounts in food, pentadecanoic acid is not described as a safety concern in any source we found. No authority sets an upper limit or a recommended intake. PubChem lists it as a flavoring agent added to food. It records a 2023 evaluation by the Joint FAO/WHO food additives committee that found no safety concern at current intake for flavoring use.

Those amounts are tiny, so this says little about supplements. The 12-week placebo-controlled trial gave 200 mg a day to 30 young adults. No significant adverse events occurred, and the supplement maker supplied the capsules.

• Little long-term data. The trials ran 12 weeks and enrolled 30 and 88 people. We found no trial in children, pregnancy, breastfeeding, older adults or people with kidney or liver disease, and no study of interactions with drugs. Ask a doctor first if you are pregnant, breastfeeding, have liver disease or take medicines.
• Pregnancy. In pregnant mice, 1% C15:0 in the diet caused mild insulin resistance and oxidative stress during lactation. That is a mouse result, but it is the only pregnancy study we found. It is a reason not to start a supplement in pregnancy without advice.
• Animal safety tests. A 13-week rat study tested an algal oil rich in C15:0 and C17:0. It found no adverse effects up to 15% of the diet, equal to over 7,500 mg/kg a day of the oil. The authors are at Burdock Group Consultants and Heliae Development. A mixture of two fatty acids is not the same as C15:0 alone.
• It is a saturated fat. FAO and WHO advise that total saturated fat should not exceed 10% of energy. The report’s findings on LDL name lauric, myristic and palmitic acids, not C15:0. Cohort studies find odd-chain fats go with lower risk and even-chain ones with higher risk. But no trial has tested C15:0 for heart disease. The foods that carry it add other saturated fats. In one trial, 50 g a day of butter raised LDL 0.42 mmol/L more than coconut oil.

How to get more pentadecanoic acid (C15:0) wisely

• Eat the foods that carry it as you would anyway. Ground beef, semi-skimmed milk and farmed salmon lead our ranking. But full-fat dairy and meat bring other saturated fats, so C15:0 is not a reason to eat more of them.
• Feed the gut bacteria with fiber. Inulin raised blood C15:0 by about 17% in a week in 16 adults. The dose of 30 g a day is more than the whole 28 g Daily Value for fiber. So it is a trial dose, not an everyday target.
• Ask before a supplement. Capsules raise blood C15:0, but the two trials are small, the first was supplied by the maker, and none tested disease. A doctor can say whether a supplement fits your health and medicines.

History of pentadecanoic acid (C15:0)

Pentadecanoic acid is an old molecule in biochemistry. A 1951 paper in the Journal of Biological Chemistry followed a carbon-14 labeled version. It studied how the acid is absorbed and carried in the lymph.

For decades after that, labs used C15:0 and C17:0 as internal standards in fat analyses. They were thought to be too rare in people to matter, according to a 2015 review.

The marker story began in 1999. That year Smedman and colleagues in Sweden showed in 62 men that C15:0 in serum tracked milk fat intake. Cohort studies then linked higher levels to less coronary heart disease (EPIC-Norfolk, 2012). They also linked them to less type 2 diabetes (EPIC-InterAct, 2014; a 16-cohort pooled analysis, 2018).

In 2017 the fiber trial added another source, propionate from gut bacteria.

The essential-fatty-acid story began in dolphins. In 2020 Venn-Watson and colleagues reported on bottlenose dolphins moved to a modified fish diet. The dolphins had lower insulin and cholesterol and higher hematocrit. C15:0 was the highest-prioritized odd-chain fat among the markers of the new diet.

The lead author is a shareholder in and employee of Epitracker and Seraphina Therapeutics. Later in 2020 a paper from the same group proposed C15:0 as essential, and the first human trials followed in 2024. In 2026 an analysis of two US cohorts with genetic data concluded that the evidence is not consistent with a causal heart benefit.

Frequently asked questions about pentadecanoic acid (C15:0)

What is pentadecylic acid, and is it the same as pentadecanoic acid?

Yes. Pentadecylic acid is an older name for pentadecanoic acid. It is also written C15:0 or 15:0, with the formula C15H30O2. It is a saturated fat with 15 carbons in a straight chain, found in small amounts in dairy fat, ruminant meat and some fish.

Gut bacteria and the liver also make it, and margaric acid (C17:0) is its odd-chain neighbor.

Is C15:0 an essential fatty acid?

Not by the usual definition. FAO and WHO name only linoleic acid and alpha-linolenic acid as indispensable, because humans cannot make them. In 2020, authors tied to a C15:0 supplement maker proposed a looser definition and said C15:0 fits.

But the liver makes some C15:0 from fiber, and we found no study that withheld it and produced a deficiency disease. A 2024 mini-review calls its essentiality controversial.

Does C15:0 lower the risk of type 2 diabetes?

Higher blood C15:0 goes with a lower risk, but that does not show that C15:0 does it. A pooled analysis of 16 cohorts (63,682 people) found 0.80 times the risk, and an umbrella review found 0.82. The same blood levels rise with dairy fat, fiber and other habits. We found no randomized trial of C15:0 on diabetes.

Do C15:0 supplements work?

They raise blood C15:0, and that is all the trials show so far. In 30 young adults, 200 mg a day for 12 weeks raised it by 1.88 µg/mL more than placebo. In 88 women with fatty liver disease, adding C15:0 to a diet lowered LDL further than the diet alone. But the diet drove most of the weight and liver-fat change.

No trial has tested diabetes, heart disease or deaths, and a supplement maker supplied the capsules in the first.

How much C15:0 should you take per day?

No health body sets an amount. The 12-week trial used 200 mg a day. That is about what 4 cups of semi-skimmed milk or nearly 2 four-ounce portions of ground beef give (our arithmetic from the USDA ranking). We found no study showing that more than food gives is needed.

Ask a doctor before starting a supplement, especially in pregnancy.

Which foods have the most C15:0?

In our USDA ranking per serving, ground beef leads with 0.11 g in 4 oz. Semi-skimmed milk follows at 0.05 g in a cup, then farmed Atlantic salmon at 0.04 g in 3 oz. Butter, cheese and yogurt are not in the ranking, but odd-chain acids make up 1.5% to 2.5% of milk fat according to a review. Fiber helps too, since gut bacteria turn it into propionate and the liver builds C15:0 from that.

Is C15:0 the same as C17:0 (margaric acid)?

No. Both are odd-chain saturated fats found in dairy fat and linked in cohorts to lower diabetes risk. But C17:0 has two more carbons than C15:0, and the links differ. In the pooled cohort analysis, diabetes risk was 0.65 times as high for 17:0 and 0.80 for 15:0. In older US adults, 17:0 but not 15:0 went with fewer cardiovascular deaths (0.77).

See margaric acid for its page.

Is C15:0 bad for you because it is a saturated fat?

Not on the evidence so far, but it has not been tested the way heart advice is. FAO and WHO say total saturated fat should not exceed 10% of energy. Their findings on LDL name lauric, myristic and palmitic acids, not C15:0. Cohorts find odd-chain fats go with lower risk and even-chain ones with higher risk.

The foods that carry C15:0 add other saturated fats. In one trial, 50 g a day of butter raised LDL by 0.42 mmol/L more than coconut oil.