The Forgotten Fat You're Probably Not Getting Enough Of
The Forgotten Fat You're Probably Not Getting Enough Of
C15:0, Paul Saladino, and the Case for Eating Like Your Ancestors
By Dr. Toni Varela, NMD | drtonivarela.com
For decades, we've been told that saturated fat is the enemy. Avoid butter. Skip the whole milk. Choose low-fat everything. But what if that advice has been costing us something we can't afford to lose?
Enter C15:0 — also known as pentadecanoic acid — a naturally occurring fatty acid found in grass-fed dairy, ruminant meat, and certain fish. It won't appear on a cereal box or in a mainstream nutrition guideline anytime soon. But the science behind it is quietly rewriting the fat conversation, and practitioners like Dr. Paul Saladino, MD have been connecting the dots between this overlooked fat, ancestral eating, and long-term vitality.
What Is C15:0 and Why Should You Care?
C15:0 is an odd-chain saturated fatty acid — and unlike the even-chain saturated fats found in processed junk food, this one behaves very differently inside your body.
Research shows C15:0 activates AMPK and inhibits mTOR — two of the most important biological switches involved in cellular repair, energy regulation, and longevity. In plain terms: it signals your cells to clean house, burn fuel more efficiently, and calm down chronic inflammation.
Large population studies have linked higher C15:0 blood levels to:
Lower risk of type 2 diabetes
Fewer cardiovascular events
Less non-alcoholic fatty liver disease (NAFLD)
Reduced chronic inflammation and hypertension
Greater overall longevity
Some researchers now consider C15:0 an essential fatty acid — meaning your body can't make meaningful amounts on its own, so it must come from what you eat. Sound familiar? That's the same category omega-3s fall into. Yet almost no one is talking about C15:0 at the dinner table.
Paul Saladino and the Animal-Based Diet
Dr. Paul Saladino is a physician and one of the loudest voices in the ancestral health movement. He began as a strict carnivore advocate and evolved into what he now calls an "animal-based" diet — a framework that centers nutrient-dense animal foods while welcoming select carbohydrates from low-toxin sources like fruit, honey, and root vegetables.
The philosophy is simple: eat the foods humans evolved eating. Foods that are rich in bioavailable nutrients, free from industrial seed oils, and packed with the fats and proteins our biology actually recognizes.
C15:0 sits at the heart of this approach — and it's one of the most compelling scientific arguments for why full-fat, grass-fed animal foods deserve a place back on your plate.
What Does a Day of Eating Actually Look Like?
Here's a realistic snapshot of an animal-based day:
Morning
Pasture-raised eggs cooked in grass-fed butter
Raw honey
Fresh fruit — mango, berries, papaya, or orange slices
Midday
Grass-fed ground beef or ribeye
Fresh-squeezed juice or coconut water
Sweet potato or another root vegetable
Evening
Grass-fed steak, wild-caught salmon, or sardines
Full-fat grass-fed dairy — whole milk, raw cheese, or more butter
More seasonal fruit or a drizzle of raw honey
A few times a week:
Organ meats — especially liver — one of the most nutrient-dense foods on the planet
What's notably off the plate:
Seed oils (canola, soybean, sunflower, corn oil)
Ultra-processed and packaged foods
Grains of any kind
High-lectin or high-oxalate plants (legumes, raw spinach, raw cruciferous vegetables)
Refined sugars and added sweeteners
How Much C15:0 Do You Actually Need?
Research points to 100–300 mg of C15:0 per day to maintain active, beneficial levels in the bloodstream. Since C15:0 makes up roughly 1–3% of dairy fat, reaching that range through food means regularly eating full-fat, grass-fed dairy — not the fat-free or low-fat versions that strip it away.
For those who avoid dairy or want to ensure optimal levels, supplemental C15:0 is available — the most well-known being Fatty15. It's a simple addition that makes the benefits accessible even outside of a fully animal-based approach.
As a naturopathic doctor, I find this especially relevant for patients who've spent years avoiding saturated fat out of habit or outdated fear — many of whom may unknowingly be running low on a nutrient their body genuinely needs.
How to Test Your C15:0 Levels
C15:0 won't show up on a standard metabolic or lipid panel. To measure it, you need a fatty acid profile — look for pentadecanoic acid (C15:0) listed within a comprehensive fatty acid analysis.
Two specimen types are available: A plasma fatty acid panel reflects recent dietary intake over days to weeks and is useful as a quick snapshot. A red blood cell (RBC) fatty acid profile reflects longer-term status, much like HbA1c does for blood sugar over 90 days. For a true picture of where a patient actually stands, RBC is the more clinically meaningful option.
Standard labs like LabCorp and Quest offer fatty acid panels, but functional medicine labs such as Genova Diagnostics, Doctor's Data, and Vibrant America provide more detailed individual fatty acid breakdowns that are better suited for clinical decision-making. The supplement company Fatty15 also offers a direct-to-consumer finger-prick home test worth knowing about.
Research suggests beneficial circulating C15:0 levels fall between roughly 0.2-0.4% of total fatty acids. Patients coming off the Standard American Diet and especially those who've spent years on low-fat diets often come in at or below the low end of that range.
I recommend pairing C15:0 with an omega-3 index on the same panel. Together they give you a comprehensive baseline of the two most commonly deficient essential fatty acids and a concrete number patients can retest after dietary changes or supplementation.
Where I Part Ways: The Case Against Vegetables
Saladino argues that bitter compounds in plants — oxalates, lectins, phytates, polyphenols — are evolutionary defense mechanisms. The plant's way of saying "don't eat me." By that logic, bitterness is a warning signal, and most vegetables should be minimized or avoided entirely.
This is where, as a naturopathic doctor, I respectfully disagree.
The missing concept here is hormesis — the well-established biological principle that mild, low-dose stressors make us stronger. Many bitter plant compounds don't harm us; they train us. Polyphenols, glucosinolates, and flavonoids found in vegetables activate powerful detoxification and antioxidant pathways in the body (notably Nrf2), and decades of research associate them with reduced cancer risk, better gut health, and lower cardiovascular disease
Using bitterness as evidence of toxicity is a bit like saying exercise is harmful because it damages muscle tissue. Technically true in isolation — but it completely misses the adaptive response that follows.
My clinical take: Bitter compounds are often the medicine, not the warning. A plate of steamed broccoli, arugula, or roasted beets is not your enemy. Where I do agree with Saladino is that not all plants are created equal — raw high-oxalate foods in large quantities, or a diet built on processed grains and legumes, is a very different conversation than whole, cooked, colorful vegetables eaten in balance.
The goal isn't to fear plants. It's to be intentional about which ones, how they're prepared, and how much.
How Much Protein Do You Actually Need?
The popular fitness rule of 1 gram of protein per pound of body weight is everywhere — but it has no strong clinical foundation as a universal target, and for patients actively trying to reduce inflammation, it may actually work against them.
Here's why: protein — particularly in large doses per meal — activates mTOR, the same cellular pathway involved in growth and inflammation. Research suggests that meals exceeding roughly 25-30 grams of protein cross a threshold that stimulates mTOR-driven inflammatory signaling in immune cells. This doesn't mean protein is bad. It means dose and distribution matter.
A more clinically useful framework:
Target 0.7–1g of protein per pound of lean body mass — not total body weight — spread evenly across meals. Here's what that looks like in practice:
A 180 lb woman with 20% body fat has approximately 144 lbs of lean body mass. Her optimal protein range is roughly 100–144g per day, distributed across 3–4 meals — not 180g, which the blanket rule would suggest.
For comparison:
RDA (bare minimum): ~0.36g per lb of body weight
Functional medicine sweet spot: ~0.54–0.73g per lb of body weight
Active adults or muscle preservation: up to 1g per lb of lean body mass
The popular "1g per lb" rule: overshoots for most people and may drive unnecessary inflammation
2 grams per lb for weight loss: The people doing this and seeing results are most likely losing weight despite the excess protein, not because of it. At that level, satiety kicks in and overall calorie intake drops naturally — that's the real mechanism. Beyond roughly 1g per lb of lean body mass, excess amino acids convert to glucose via gluconeogenesis, mTOR stays chronically elevated, and the liver and kidneys carry an unnecessary burden. More protein is not always better. Smarter protein is.
Source matters as much as amount. Grass-fed beef, wild-caught fish, pasture-raised eggs, and quality organ meats provide complete amino acid profiles with far less metabolic noise than processed protein powders or conventional factory-farmed meat.
The goal is enough protein to build, repair, and thrive — not so much that you're chronically stimulating inflammatory pathways with every meal.
Weight Loss, GLP-1 Medications, and the Root Cause Question
No conversation about diet and weight loss in 2024 is complete without addressing the elephant in the room: GLP-1 medications like semaglutide (Ozempic, Wegovy).
Saladino is openly critical of them — and in certain contexts, his criticism is clinically sound. His core argument: these medications suppress appetite without addressing the root cause of why someone is struggling with weight in the first place. Poor food quality, seed oils, ultra-processed ingredients, and metabolic dysfunction driven by decades of the Standard American Diet don't get fixed by a weekly injection. And when the medication stops, the weight almost universally returns — because nothing upstream has changed.
He also raises a legitimate concern about muscle mass loss. Rapid weight loss through appetite suppression alone, without a high-quality protein foundation and resistance training, risks losing lean muscle alongside fat — which worsens metabolic rate long-term.
Where the clinical evidence supports GLP-1s
That said, the data on semaglutide in patients with genuine obesity and cardiometabolic risk is significant. Large clinical trials have shown meaningful reductions in body weight, cardiovascular events, and metabolic markers in this population. For patients with significant metabolic disease who have struggled to make dietary changes despite support, GLP-1 medications can be a legitimate bridge — not a shortcut.
The problem isn't the medication itself. It's the increasingly common off-label use by otherwise healthy individuals seeking aesthetic weight loss, often driven by social media trends rather than clinical need. Used without a dietary foundation, it's a temporary fix at best.
Where I Stand on GLP-1s:
The question I ask every patient considering a GLP-1 medication is this: "What would need to change in your diet and lifestyle for you to not need this?" That question alone is often more therapeutic than any prescription.
If a patient is already on a GLP-1, a whole-food, grain-free, animal-based approach is actually an excellent complement — it addresses the root cause while the medication provides a metabolic bridge. Pair it with adequate protein distribution to protect lean muscle, resistance training, and the lab panel we discussed, and you have a genuinely comprehensive strategy.
Medications can open the door. Food quality is what keeps it open.
Is This Diet Right for You? Keto, Animal-Based, or Something Better?
If you're coming from the Standard American Diet — processed food, refined grains, fast food, seed oils — the idea of overhauling everything at once is overwhelming. And frankly, it rarely works.
In my practice, I don't hand patients a rigid meal plan and send them home. I use a phased, whole-food approach that meets people where they are and builds from there.
Phase 1 — Remove the worst offenders
Seed oils, ultra-processed food, sugary drinks, and refined grains go first. This single step alone moves the needle dramatically — and it's achievable without patients feeling deprived.
Phase 2 — Upgrade quality, not just category
Swap conventional proteins for grass-fed, pasture-raised, and wild-caught options. Same familiar foods — just better sourced. Organic produce where possible. This is where the foundation of real nourishment starts.
Phase 3 — Shift carbohydrates intentionally
Out go the grains entirely. In come fruit, root vegetables, and sweet potatoes — whole food carbohydrates that come packaged with fiber, vitamins, and minerals instead of empty calories.
Phase 4 — Add therapeutic fats
Grass-fed butter, olive oil, avocado, full-fat dairy. This is where C15:0 enters the picture naturally, and where patients often notice the most dramatic shifts in energy and satiety.
Phase 5 — Personalize and optimize
Organ meats, targeted supplementation, meal timing, stress and sleep support. This is the fine-tuning phase — and it looks different for every person.
How does this compare to keto?
Keto is therapeutically powerful — particularly for insulin resistance, neurological conditions, and rapid metabolic reset. But strict carbohydrate restriction eliminates fruit, which has genuine nutritional value, and is difficult to sustain long-term for most people.
The animal-based approach is less restrictive — it welcomes fruit and honey as carbohydrate sources — but still eliminates grains and processed foods. My approach sits in a similar space: whole food, grain-free, quality-first, and personalized by what your labs actually show.
I don't prescribe diets. I use your biology to figure out what your body is asking for — then we build from there.
Using Labs to Personalize Your Diet
Not every dietary approach is right for every body. This is exactly why I use functional lab markers to guide my recommendations rather than applying a one-size-fits-all protocol.
Here's what I look at:
Metabolic and insulin markers
Fasting insulin and HOMA-IR are the most underutilized markers in conventional medicine. They reveal how insulin resistant someone is long before glucose or HbA1c shifts — and they directly determine how low-carb a patient actually needs to go.
Lipid particle sizing (NMR LipoProfile)
Standard cholesterol panels miss too much. LDL particle number, small dense LDL, and HDL particle size give a far more accurate picture of cardiovascular risk. Triglycerides, in particular, are a key signal for how well someone is metabolizing carbohydrates — high triglycerides almost always mean carbs need to come down.
Inflammation markers
hs-CRP and ferritin (often overlooked as an inflammation signal beyond iron status) reveal the degree of systemic inflammation driving chronic disease.
Fatty acid status
Omega-3 index and C15:0 levels via a fatty acid panel tell us directly whether the patient is getting enough of the fats their cells need to function — or whether they're running on empty.
Other key markers
ApoB, homocysteine, vitamin D, a full thyroid panel (TSH, free T3, free T4), and liver enzymes (ALT/AST) round out the picture — especially for patients coming off years of a Standard American Diet where NAFLD, subclinical hypothyroidism, and nutrient deficiencies are common findings.
These markers, taken together, tell a story. And that story determines the dietary strategy — not the other way around.
How to Actually Track What You're Eating
Knowing what to eat is one thing. Knowing whether you're actually hitting your targets is another. Tracking macros — protein, fat, and carbohydrates — doesn't have to be complicated, and for most patients it's one of the most eye-opening things they can do in the first few weeks of a dietary change.
Here are the tools I recommend:
Cronometer — the best option for patients focused on nutrient density, not just calories. It breaks down micronutrients, fatty acid profiles, and amino acid content, so you can see not just how much you're eating but what you're actually getting from your food. Free version is excellent.
MyFitnessPal — the most beginner-friendly option. Massive food database, easy barcode scanning, and a familiar interface. Less detailed on micronutrients but ideal for patients just getting started who need simplicity.
Carb Manager — well-suited for lower-carb and grain-free approaches. Intuitive and visually clear on carbohydrate breakdown.
My recommendation for patients new to tracking: Start with protein only for the first 2–4 weeks. Hit your protein target consistently before layering in awareness of carbs and fats. Tracking everything at once from day one is overwhelming — and overwhelm leads to abandonment. Build the habit first, then build the detail.
Frequently Asked Questions
Is C15:0 the same as other saturated fats I've been told to avoid?
No. Most of the saturated fat research that generated the "fat is bad" narrative focused on even-chain saturated fats found in processed and fried foods. C15:0 is an odd-chain fatty acid with a distinctly different metabolic profile and a growing body of evidence supporting its benefit — not its harm.
Do I need to go fully carnivore or animal-based to benefit?
Not necessarily. Incorporating full-fat grass-fed dairy, quality meats, and fatty fish into an otherwise balanced whole-food diet can meaningfully raise your C15:0 levels. The goal isn't perfection — it's consistent improvement.
What about cholesterol? Won't eating more fat raise my numbers?
This is one of the most common concerns I hear, and the answer is nuanced. Dietary fat affects different cholesterol subtypes in different ways. Many patients who shift to whole-food, animal-based fats see improvements in their lipid profiles — particularly in particle size and triglycerides. This is something we look at individually, not through a one-size-fits-all lens.
Should I really avoid vegetables?
In my practice, no — not categorically. I align with the emphasis on quality animal foods and C15:0, but I don't subscribe to the idea that vegetables are inherently harmful. Bitter plant compounds can be powerful medicine when the right foods are chosen and prepared well. Context and individuality always matter.
Is 1 gram of protein per pound of body weight the right target?
For most people, no — especially if inflammation is a concern. A better target is 0.7–1g per pound of lean body mass, distributed across meals and capped at roughly 25–30g per sitting to avoid over-activating mTOR inflammatory pathways. Quality of protein source matters just as much as quantity.
What's my take on Ozempic and GLP-1 medications?
They have a legitimate clinical role for patients with significant metabolic disease and cardiometabolic risk. But used as a shortcut without addressing diet and lifestyle, the weight returns when the medication stops — because nothing upstream has changed. The better question is always: what needs to change so you don't need this long-term? That's the conversation I have with every patient.
Can I just take a C15:0 supplement instead of changing my diet?
A supplement like Fatty15 can help fill a gap, but it works best alongside a nutrient-dense, whole-food diet. Food first is always the foundation — supplements are exactly that: supplemental.
Is this approach safe for everyone?
Most people do well with a whole-food, grain-free approach, but individual health history, metabolic goals, and underlying conditions all matter. This is exactly why personalized guidance from a naturopathic doctor makes all the difference.
My Take as a Naturopathic Doctor
The animal-based framework resonates deeply with naturopathic medicine because it honors a foundational principle: the body knows how to heal when given the right raw materials. Whole, nutrient-dense, ancestrally appropriate foods are some of the most powerful tools we have.
I take what's compelling from Saladino's work — the C15:0 science, the emphasis on grass-fed animal foods, the rejection of seed oils and ultra-processed ingredients — and I integrate it with a broader naturopathic lens that still honors the healing potential of the plant kingdom, uses labs to guide individualization, and meets patients where they actually are.
Not every protocol fits every person. That's exactly the point.
Your great-grandparents ate butter without apology and grew vegetables in the backyard. Maybe it's time we did the same.
Ready to Optimize Your Nutrition from the Inside Out?
If you're curious whether an animal-based approach, C15:0 optimization, or a personalized whole-food nutrition strategy is right for you — I'd love to help you figure that out.
Book a consultation with Dr. Toni Varela, NMD and let's use your labs to build a plan that works with your biology, not against it.
Because the best diet isn't the one that's most popular — it's the one that's right for you.
This post is for educational purposes only and does not constitute personalized medical advice. Always consult with a qualified healthcare provider before making significant changes to your diet.