New book explores how an overlooked saturated fatty acid, C15:0, could play foundational role in maintaining cellular health and resilience. 
A serendipitous discovery made while caring for dolphins has led to a renewed interest in an unexpected nutrient – pentadecanoic acid, or C15:0 – which is now the subject of a new book claiming it may be critical to healthy aging.
In The Longevity Nutrient: The Unexpected Fat That Holds the Key to Healthy Aging, Dr Stephanie Venn-Watson, a veterinary epidemiologist and former US Navy researcher, outlines her path from marine mammal medicine to the identification of a fatty acid that may play a role in mitigating several hallmarks of aging in humans.
The premise of the book rests on a central hypothesis: that C15:0, a long-chain saturated fatty acid found naturally in full-fat dairy and some fish, may be an essential nutrient for human health – one that has been declining in modern diets as public health guidance has encouraged the reduction of saturated fats. Venn-Watson argues that the nutrient’s deficiency may be contributing to a widespread syndrome she terms “Cellular Fragility Syndrome,” which could help explain rising levels of metabolic disease and premature aging, particularly in younger populations.
From helping to improve dolphin health to human aging
The narrative begins with the study of long-lived Navy bottlenose dolphins. Seeking to understand why some dolphins aged more healthily than others, Venn-Watson employed metabolomic analysis on archived blood samples to identify biomarkers associated with slower aging trajectories. Among these markers, C15:0 emerged as a common denominator, and subsequent laboratory and clinical research led to its classification as the first essential fatty acid to be identified in nearly a century.
While historically overlooked – likely due to its presence in foods commonly associated with negative health messaging – C15:0 is described in the book as a nutrient with significant implications for systemic resilience. Venn-Watson and her collaborators found that this fatty acid is involved in a wide range of cellular functions that occur with age: from impaired mitochondrial performance to inflammation, and from epigenetic alterations to increased membrane fragility.
Mechanisms of action and biological plausibility
C15:0 appears to exert its influence via several well-established biological pathways associated with longevity. According to the book and associated studies, it activates AMPK – a protein complex involved in energy sensing and metabolic regulation – and inhibits mTOR, a pathway linked to cellular senescence and aging-associated diseases [1]. These effects align it with other known longevity-associated compounds, though with fewer reported safety concerns compared with pharmacological agents such as rapamycin.
Moreover, C15:0 is reported to improve cell membrane integrity – an effect that supports the so-called Cell Membrane Theory of Aging, which posits that the stability and composition of lipid bilayers play a fundamental role in determining lifespan [2]. By resisting lipid peroxidation and mitigating ferroptosis, a form of cell death driven by oxidative stress, C15:0 may help preserve cellular function under stress and delay age-related decline.
Fatty15 is a pure C15:0 supplement
The molecule also seems to have a role in maintaining immune homeostasis and gut microbiome composition – two areas increasingly recognized for their influence on aging. In clinical trials, oral supplementation with purified C15:0 has been shown to raise C15:0 levels, resulting in improved markers of liver function, lowered LDL cholesterol and improved red blood cell health within a matter of weeks, supporting the plausibility of its healthspan benefits [3].
Addressing a modern dietary deficiency
A key theme of The Longevity Nutrient is the idea that shifts in dietary patterns – particularly the reduction of whole-fat dairy and other natural sources of C15:0 – may have unintended consequences. Venn-Watson presents a compelling case for C15:0 deficiency as a contributing factor to metabolic dysregulation and age-related diseases. This condition, which she names Cellular Fragility Syndrome, may affect up to a third of the global population [4]. While the diagnosis remains conceptual, the clinical markers she associates with it – oxidative stress, inflammation, mitochondrial dysfunction and impaired cell membrane function – are broadly accepted as contributors to age-related pathology.
Dr Stephanie Venn-Watson is the author of The Longevity Nutrient
Importantly, the book does not advocate for a wholesale return to high-fat diets. Instead, it emphasizes the distinction between C15:0 and other saturated fats, highlighting its unique molecular properties and suggesting that moderate, targeted supplementation may be a safer and more effective route than broad dietary changes. Indeed, this is why the US Navy funded Venn-Watson’s work to develop a pure C15:0 supplement.
Scientific caution and the road ahead
Though the book presents a compelling argument and draws on a growing body of peer-reviewed research, some caution is warranted. As with many emerging longevity interventions, long-term outcomes in diverse human populations remain to be fully established. Because C15:0 has been in our food supply for so long, unlike other longevity interventions, there are a good number of meta-analyses (studies including a dozen or more prospective cohort studies that followed tens of thousands of people over more than a decade), which repeatedly showed that people with higher C15:0 levels have a lower risk of developing type 2 diabetes, heart disease and fatty liver disease. The evidence to date – though promising – derives largely from animal models, in vitro studies, large epidemiological studies and relatively short-term human trials. Further validation through larger, longer-duration studies is warranted before C15:0 can be firmly positioned alongside established dietary recommendations.
Nonetheless, The Longevity Nutrient offers a thought-provoking exploration of the intersection between nutrition, cellular biology and aging. Venn-Watson’s unique background in veterinary science provides a distinct vantage point – one that challenges conventional assumptions about saturated fats and invites renewed scrutiny of how nutritional deficits may silently influence the trajectory of human health over the lifespan.
The book is already being well received by the longevity community. Dr Mark Hyman, Co-Founder and Chief Medical Officer, Function Health, 15x New York Times bestselling author of Young Forever, writes: “Dr Stephanie Venn-Watson has made a groundbreaking, once-in-a-century discovery that changes how we can age for the better, at all stages of life. While improving the health of older dolphins, she unexpectedly discovered the crucial ingredient we all need to slow aging and fight chronic aging-associated diseases. The Longevity Nutrient tells the rest of the story. The book entertains as it enlightens, with impressively robust science that has positively affected my own life, and I guarantee you won’t look at saturated fat the same way again.”
In a field often dominated by high-profile molecules such as NAD+, metformin and senolytics, C15:0 emerges here as a quiet but compelling contender – an unassuming nutrient with an expanding portfolio of biological relevance. Whether it will prove to be as influential in long-term health as it is in current studies remains an open question, but the case made in The Longevity Nutrient is one that warrants attention.
The Longevity Nutrient by Dr Stephanie Venn-Watson, DVM, MPH, is available from the fatty15 website, Amazon, Barnes & Noble, Bookshop or all good booksellers.
Photographs courtesy of fatty15
[1] https://www.mdpi.com/2072-6643/15/21/4607
[2] https://www.mdpi.com/2218-273X/11/2/241
[3] https://jn.nutrition.org/article/S0022-3166(24)00411-5/fulltext
[4] https://www.mdpi.com/2218-1989/14/7/355
