What is the best source of C15, and why does it matter?

November 22, 2025 •

2 min read

Recent studies in Navy dolphins linked higher C15:0 levels to healthier aging outcomes, bringing attention to this unique fatty acid. This sparked wider interest in pentadecanoic acid, leading many to ask: what is the best source of C15 for human health?

Quick Summary

Full-fat dairy is the primary dietary source of C15, but modern farming practices may have reduced its content. Supplements offer a concentrated and highly bioavailable form of C15, providing an alternative to consuming large quantities of dairy fat.

Key Points

Source Varies by Diet: The best source of C15 depends on your goals, with full-fat dairy and certain meats serving as natural sources and supplements providing a concentrated alternative.
Supplements Offer Efficiency: For a potent and highly bioavailable dose without the excess calories of food, C15 supplements are the most effective method.
Dairy Fat is a Primary Natural Source: Whole milk, butter, and cheese from ruminant animals are the richest natural food sources, though content may vary with farming practices.
Food Levels are Declining: Shifts toward low-fat dairy and modern agricultural methods using grain feed have reduced the natural C15 content in many foods.
Health Benefits Are Promising: Research suggests C15 is correlated with better metabolic, liver, and cardiovascular health, but more human trials are needed to confirm these benefits.
Not an Officially 'Essential' Nutrient: Although some research suggests C15 is a candidate for essential status, it is not yet recognized as such by major nutrition authorities.

Understanding C15: The Odd-Chain Saturated Fatty Acid

Pentadecanoic acid, or C15:0, is an odd-chain saturated fatty acid found in the fat of ruminant animals. It has gained attention for its potential role in cellular health and longevity pathways, unlike many even-chain saturated fats.

Dietary Sources of C15: Food vs. Supplements

Increasing C15 levels can be done through diet or supplementation, each with pros and cons.

Food Sources

The primary dietary sources of C15 are fats from ruminant animals. These include:

Full-fat dairy: Products like whole milk, butter, and cheese are the richest natural sources. However, C15 levels in dairy may have decreased due to modern farming and a preference for low-fat products.
Ruminant meat: Grass-fed beef and lamb contain smaller amounts.
Certain fish: Fatty fish also provide C15.

Supplementation

C15 supplements, often in a free fatty acid form, offer a direct and concentrated way to increase intake. This can be a practical option to achieve a specific dose without excessive calories or fat, and many pure C15 supplements are vegan. Note that some research on these supplements is linked to their manufacturers.

Natural Sources vs. C15 Supplements: A Comparison

Here is a comparison to help determine what is the best source of C15 for your needs:


Feature	Dietary Sources (Full-Fat Dairy/Meat)	C15 Supplements (e.g., FA15)
C15 Concentration	Requires high intake for meaningful levels.	High concentration provides a meaningful daily dose in a small amount.
Absorption	C15 is bound in food and requires digestion.	C15 is in a more readily absorbed free fatty acid form.
Additional Nutrients	Contains other nutrients from whole foods.	Offers C15 in isolation.
Associated Calories	High caloric load for a meaningful dose.	Very low caloric impact.
Saturated Fat Profile	Includes other saturated fats.	Pure C15.
Source Dependence	C15 content can vary based on factors like animal feed.	Consistent, controlled dosage.
Cost	Cost of high quantities can be significant.	Typically more expensive per milligram, but efficient for higher doses.

How to Increase C15 Intake

To increase C15 intake through whole foods, focus on grass-fed, full-fat dairy and incorporate ruminant meats and fatty fish. For a consistent and targeted dose, a pure C15 supplement is the most direct approach, especially for those with dietary restrictions or who prefer not to consume large amounts of dairy.

Conclusion: Which Source is Best for You?

While dietary sources like full-fat dairy and meat provide C15, supplementation is generally the most effective way to achieve and maintain optimal levels. This is particularly relevant given the potential decline of C15 in modern food sources and concerns about the caloric intake from large quantities of dairy. For those prioritizing a targeted increase in C15 without significant dietary changes, a pure C15 supplement is often the preferred choice. The "best" source ultimately depends on individual dietary needs, health goals, and preferences. Regardless of the source, ongoing research highlights the potential importance of this unique fatty acid for cellular health.

Outbound link: {Link: NIH https://pmc.ncbi.nlm.nih.gov/articles/PMC10649853/}

Frequently Asked Questions

The highest natural sources of C15 fatty acid are full-fat dairy products from ruminant animals, including butter, whole milk, cream, and aged cheeses like cheddar, Swiss, and Parmesan.

C15 supplements provide a concentrated, bioavailable dose of pure C15 without the additional calories and saturated fat found in whole foods. For achieving a specific, optimized C15 level, a supplement is often more efficient than relying solely on food sources.

C15 levels in food sources have declined due to several factors. These include a widespread consumer shift towards low-fat and plant-based diets, and changes in animal farming that favor grain-based feed over grass.

The scientific community is still debating C15's status. While some studies, often linked to supplement manufacturers, promote it as an essential nutrient, major nutritional authorities have not yet officially recognized it as such.

Emerging research suggests C15 may have anti-inflammatory properties, improve metabolic function, and support liver and cardiovascular health. It's also been shown in cellular studies to strengthen cell membranes and activate longevity pathways.

While C15 is predominantly found in animal products, small amounts have been detected in some plant-based foods, though not enough to significantly boost circulating levels. The primary C15 supplement on the market is vegan-friendly.

Recommended daily intake varies in studies, but researchers typically suggest aiming for a dose between 100 and 300 mg to achieve and maintain meaningful circulating levels. This is most easily accomplished through supplementation.