Fatty15 is a dietary supplement containing a single active ingredient: pentadecanoic acid, a 15-carbon saturated fatty acid also known as C15:0. The supplement delivers a pure, concentrated form of this fatty acid, which is found naturally in trace amounts in whole-fat dairy, beef, lamb, and some fish. Researchers have proposed that C15:0 may be an essential fatty acid, meaning the body needs it but cannot produce enough on its own, placing it in the same category as the omega-3 and omega-6 fatty acids most people are already familiar with.
What C15:0 Actually Is
Pentadecanoic acid is a straight-chain saturated fatty acid with 15 carbon atoms. Unlike omega-3s, which are polyunsaturated fats with multiple double bonds that make them liquid at room temperature and vulnerable to oxidation, C15:0 has no double bonds. That structural difference matters: it makes C15:0 chemically stable, resistant to a type of damage called lipid peroxidation that can harm cells. This stability is a core part of the argument for why C15:0 behaves differently in the body than other supplemental fats.
C15:0 is classified as an odd-chain fatty acid, which is unusual. Most fatty acids in our diet have even numbers of carbon atoms (think of the 16-carbon palmitic acid or 18-carbon stearic acid). Odd-chain fatty acids are broken down through a different metabolic pathway, and that difference turns out to have meaningful biological consequences.
How It Works in the Body
C15:0 appears to act on cells through several distinct mechanisms, which is part of why it has attracted attention from longevity researchers.
First, it integrates directly into cell membranes. Because it’s a stable saturated fat, it reinforces the structural integrity of the membrane and reduces its susceptibility to oxidative damage. By stabilizing membranes this way, C15:0 may slow premature cellular aging.
Second, it supports mitochondrial function through a pathway unique to odd-chain fatty acids. When C15:0 is broken down for energy, the final product feeds into the cell’s main energy cycle at a specific entry point called complex II. This replenishes key intermediates that keep energy production running smoothly. In cell studies, optimal C15:0 supplementation reduced levels of harmful mitochondrial byproducts (reactive oxygen species) by roughly 20% to 30% compared to unsupplemented cells, suggesting the mitochondria were running more efficiently with less “exhaust.”
Third, C15:0 interacts with several cellular signaling pathways that are well-studied targets in aging and metabolic health. It activates AMPK, a cellular energy sensor that triggers repair and recycling processes. It inhibits mTOR, a growth-signaling pathway whose suppression is linked to longer lifespan in animal studies. These are the same two pathways targeted by metformin and rapamycin, two drugs that dominate longevity research. C15:0 also activates receptors involved in regulating metabolism and lipids, and it dials down inflammatory signaling pathways.
What Clinical Research Shows
A randomized controlled trial in young adults with overweight and obesity tested C15:0 supplementation over 12 weeks. The most striking results appeared in participants whose blood levels of C15:0 rose above a certain threshold. In that group, a key marker of liver stress dropped by 29 units, while it stayed flat in the placebo group. A second liver enzyme marker dropped by 6 units. Hemoglobin levels also increased by 0.6 g/dL in the threshold group, compared to a slight decline in both the placebo and the group that didn’t absorb enough C15:0 to cross the threshold.
Across all supplemented participants, another liver enzyme called GGT decreased by an average of 11 units relative to placebo, even after adjusting for body weight changes. These liver markers are commonly elevated in people with metabolic stress, fatty liver, or early metabolic syndrome, so the reductions are clinically meaningful.
How C15:0 Compares to Omega-3
The comparison to omega-3 fatty acids (specifically EPA, the type found in fish oil) comes up frequently in C15:0 research, and the differences are notable. In a head-to-head study using 12 human cell systems designed to model different diseases, C15:0 was non-toxic to cells at every concentration tested. EPA, by contrast, was toxic to four of the 12 cell systems at the highest concentration.
This difference traces back to chemistry. EPA’s multiple double bonds make it prone to lipid peroxidation, especially at higher doses and in older individuals. C15:0, with zero double bonds, doesn’t carry that risk. While EPA does have well-established anti-inflammatory benefits, the peroxidation vulnerability is a meaningful tradeoff. C15:0’s stability at high concentrations, combined with its membrane-strengthening properties, is part of why some researchers frame it as a complement or even an alternative to omega-3 supplementation for certain outcomes.
Where C15:0 Occurs in Food
You can get small amounts of C15:0 from diet, but the concentrations are low. Dairy fat contains about 1% pentadecanoic acid. Beef, veal, lamb, and mutton fat contain it at similar levels. It also shows up in chicken fat, lard, marine and freshwater fish, fish oils, canola oil, and even a few vegetables like cabbage and cucumber, as well as seaweed.
The practical challenge is that you’d need to consume a substantial amount of whole-fat dairy or red meat daily to reach the blood levels associated with benefits in clinical trials. This is the core rationale behind a concentrated supplement: it delivers a meaningful dose of pure C15:0 without the calories, saturated fat load, or dietary constraints that come with trying to get it from food alone. The clinical trial data suggests that simply eating some butter or whole milk may not raise blood levels enough to cross the effectiveness threshold.
What Makes It “Essential”
The case for classifying C15:0 as an essential fatty acid rests on a few pillars. Population-level studies have consistently linked higher circulating C15:0 levels with lower rates of type 2 diabetes, cardiovascular disease, and metabolic syndrome. Blood levels of C15:0 have been declining in populations that shifted away from whole-fat dairy over the past several decades, paralleling rises in metabolic disease. The body produces very little C15:0 on its own, meaning dietary intake is the primary source. And deficiency in C15:0 appears to correlate with worse health outcomes across multiple organ systems.
This framing is still relatively new in nutritional science, and C15:0 hasn’t received official essential fatty acid designation from regulatory bodies. But the accumulating evidence has been enough to shift the conversation about odd-chain saturated fats from “irrelevant trace nutrient” to “potentially important gap in modern diets.”