I’ve been lactose intolerant for five or six years, and I’ve cut almost all dairy out of my life. (Pizza is the exception. It’s pizza!!) I take calcium pills to make up for the milk and cheese.
What I didn’t know until recently is that dairy fat is also one of the main sources of C15:0, a saturated fatty acid researchers are studying for healthy aging. So I tested fatty15, the best-known C15:0 supplement, for 60 days before writing this Fatty15 review.
I also read the research behind it, including the cell study the company loves to cite and the small human trials that get a lot less airtime.
My Quick Fatty15 Review Verdict
I like it, and I’m going to keep taking it. I’ve had more energy in the mornings (I’m on the treadmill hours earlier than I used to be), and I love the refill system. But fatty15’s website makes it sound like a magic pill, and the human data isn’t there yet.
If you avoid dairy like I do, it’s a low-risk thing to try. If you drink a ton of milk, skip it. You’re likely already getting C15:0 from your food.
I’m taking it for a full year and will update this post with my 12-month results.
| Dose | 100 mg C15:0 (pentadecanoic acid) per capsule, one a day |
| Capsule | Vegan, dairy-free |
| Price | $119.95 every 90 days on subscription (about $1.33 a day) |
| Packaging | Glass bottle on your first order, refill pouches after that |
| Where to buy | fatty15’s website |
What Is Fatty15?
Fatty15 is a once-a-day pentadecanoic acid supplement: 100 mg of pure C15:0 in a small vegan capsule. The company behind it, Seraphina Therapeutics, was cofounded by Dr. Stephanie Venn-Watson, who got interested in C15:0 while caring for Navy dolphins. Some of the older dolphins were aging healthier than others, and their C15:0 levels turned out to be part of the story.
What is C15:0 (pentadecanoic acid)?
C15:0 is an odd-chain saturated fat with 15 carbon atoms. You get small amounts from dairy fat and some fish. It’s so tied to dairy that scientists use blood C15:0 levels as a marker of how much dairy fat someone eats.
One thing to know before you buy: fatty15 calls C15:0 an essential fatty acid. That’s the company’s position, not settled science. The two fatty acids nutrition experts have long recognized as essential are linoleic acid (an omega-6) and alpha-linolenic acid (an omega-3). C15:0 isn’t an omega-3, so don’t toss your fish oil for it.
Why I Started Taking a C15:0 Supplement
When I quit dairy, I added calcium pills and called it a day. It never occurred to me that I was cutting out a fatty acid too.
The cell membrane pitch is what got me. Fatty15’s argument is that C15:0 helps strengthen cell membranes against lipid peroxidation (fats in your cells getting damaged by oxidation), one of the ways cells break down as we age. I wanted to see if I could feel a difference.
This isn’t my first supplement review (my Live It Up greens powder review was a lot more fun to taste test), but it’s the first one I tried to fill a gap I created by cutting something out of my diet.
My 60-Day Fatty15 Results
The biggest change I’ve noticed is energy. My cat wakes me up around 6 a.m. some mornings (she’s cute, so I allow it), and lately I’m on the treadmill by 7. Before fatty15, I usually didn’t get on it until somewhere between 9 and 11 a.m.
I can feel a difference in my body. I can’t prove the capsule is the only reason, since two months is short and energy has a lot of inputs. That’s why I’m keeping this going for a full year.
What the Science Says About C15:0
Fatty15 says it’s backed by a ton of studies and patents, and that’s true. What matters is what kind of studies they are.
The cell study everyone cites
The big one is a 2023 paper in the journal Nutrients by Dr. Venn-Watson and Dr. Nicholas Schork, comparing C15:0 to rapamycin, metformin and acarbose, drugs being studied for longevity. The researchers ran each one through 12 human cell-based systems that mimic different diseases, measuring 148 biomarkers at four doses.
C15:0 had 36 clinically relevant activities across 10 of the 12 cell systems. Rapamycin, the drug longevity researchers are most excited about, had 32. At their best doses, C15:0 and rapamycin shared 24 activities, including anti-inflammatory and antifibrotic ones.
That’s a cool result. It was also done on cells in a lab, not in people, and the lead author cofounded the company that sells fatty15. Neither of those makes the study wrong. But “it acts like rapamycin in a dish” is a long way from “it’ll slow your aging.”
What happened when people took it
The human trials are smaller and more modest. In a 2024 trial out of UC San Diego and Rady Children’s Hospital, 20 young adults with overweight or obesity took 200 mg of C15:0 a day for 12 weeks, and 10 took a placebo. The supplement raised their blood C15:0 levels and improved one liver blood test (GGT). It made no significant difference in weight, LDL cholesterol, blood sugar or the inflammation marker CRP.
Nobody had a significant side effect. The trial was supported by the NIH and by Seraphina Therapeutics, which supplied the capsules.
A second trial, called TANGO, followed 88 women with fatty liver for 12 weeks. Women on a Mediterranean-style diet lost weight and liver fat whether or not they added C15:0, though the C15:0 group got an extra drop in LDL cholesterol. The diet did most of the heavy lifting.
There’s also a large study led by Cambridge and Tufts researchers that linked higher blood levels of dairy-fat markers, C15:0 included, to a lower risk of type 2 diabetes. People with high levels aren’t necessarily healthier because of the C15:0, though. A pill needs its own trials to prove that.
So does fatty15 work?
For raising your C15:0 levels, yes. That part’s proven. For the bigger promises like longevity and disease prevention, the evidence is early, and I wouldn’t let anyone tell you it’s settled.
Fatty15 Pros and Cons
Pros
- The refill system. Your first order comes with a reusable glass bottle, and after that your capsules arrive in refill pouches, so you’re not stockpiling empty pill bottles. I LOVE this.
- One tiny vegan capsule a day, no powder to mix.
- More morning energy over my first 60 days.
Cons
- It’s pricey, roughly $1.26 to $1.67 a day depending on how you buy.
- Most of the research comes from the founder or is funded by the company.
- The human trials are small and short, so long-term benefits and safety are unproven.
- The 30-day trial kit automatically rolls you into a 90-day subscription.
Fatty15 Ingredients and How I Take It
The ingredient list is short. Each capsule has 100 mg of FA15, fatty15’s patented pure form of pentadecanoic acid, in a vegan capsule. You take one a day, with or without food.
I take mine first thing in the morning before breakfast, alongside my allergy pills. Pairing it with pills I already take every day means I haven’t missed a dose.
How Much Does Fatty15 Cost?
I’m on the subscription, which is $119.95 every 90 days as I’m writing this (about $40 a month). If you’d rather test it first, the 30-day trial kit is $49.95, and it rolls into that same subscription unless you cancel. A 90-day starter kit without a subscription is $149.95, and the annual kit brings it down to about $1.26 a day. Shipping is free.
Worth it if you’ve cut out dairy and want to cover that gap. Skip it if money’s tight, because the evidence doesn’t justify stretching your budget for it.
Who Should Take Fatty15 (and Who Should Skip It)
Worth trying if you avoid dairy (lactose intolerant or vegan) and you’re interested in healthy aging. Skipping dairy doesn’t make you deficient, since there’s no official C15:0 requirement. It does mean you’re missing one of the main food sources, which is why I think this group gets the most out of it.
Skip it if you already eat a lot of whole-fat dairy. Also skip it if you’re hoping to lose weight or fix your blood sugar, since the trial that tested those didn’t find a difference.
Talk to your doctor first if you’re pregnant or breastfeeding, have a liver or metabolic condition, or take several medications. The trials so far were too small and short to say how it plays with those. And be a little skeptical of any at-home test that says your C15:0 is “low.” There’s no official deficiency cutoff.
Fatty15 FAQ
Is fatty15 legit?
Yes. It’s a real product from a real company with published research behind it. The fair criticism is that much of that research comes from the company’s own founder, and the big longevity claims are ahead of the human evidence.
Does fatty15 work?
It reliably raises blood C15:0 levels, and one small trial found it improved a liver blood test. The longevity and healthy aging claims come mostly from cell and animal studies. I’ve felt more energetic over 60 days, but that’s one person’s experience.
What does fatty15 do for you?
The theory is that C15:0 helps protect cell membranes and calm inflammation, which could support cell health as you age. In people, the proven effect so far is higher C15:0 levels, with early signals for liver enzymes and LDL cholesterol.
Is C15:0 an essential fatty acid?
Fatty15 says yes. Mainstream nutrition science hasn’t officially recognized it as one. The established essential fatty acids are linoleic acid and alpha-linolenic acid.
What are the most common fatty15 complaints?
Price is the big one, and it’s mine too. The other is the trial kit auto-enrolling you in a 90-day subscription, so check your account settings after you order. You can cancel or change your subscription from your account on the fatty15 website.
When should I take fatty15?
Fatty15 says you can take it with or without food. I take mine in the morning before food, with my allergy pills, because it’s easiest to remember with something I already do.
Where can I buy fatty15?
Fatty15 sells direct on its website, which is also the easiest way to get the refill pouches.
How long does it take fatty15 to work?
The UC San Diego trial ran for 12 weeks. I noticed more energy within my first 60 days, but I’m giving it a full year before I call it.
My Final Fatty15 Review
I’d recommend fatty15, with my eyes open. If you’ve cut out dairy like I have, it’s an easy way to get C15:0 back in your diet. I’ve felt the difference in my energy, and the refill pouches mean I’m not drowning in empty bottles. If you were hoping for a magic anti-aging pill, the science isn’t there yet on these products.
If you want to try it, grab fatty15 here. I’ll be back with my one-year update, and in the meantime you can find the rest of my wellness reviews here. Have you tried fatty15 or another C15:0 supplement? Drop a comment below and tell me how it went.
