The Fat Your Brain Might Be Missing: Essential Fatty Acids, Mood, and the Surprising Story of C15

Hi there—and welcome back. I’m Dr. Cindy Libert, and today we’re diving into something that’s close to home for me… and honestly something I think more people need to hear about.

If you care about your brain, want to optimize your mood, and you want to age well—you’re in the right place.

My “pause and take a deeper look” moment

Like so many of you, the early days of the pandemic stretched me thin. I was holding a lot—trying to keep my medical practice going, attempting to homeschool my children, staying anchored and grounded… and in the midst of it all, I hit a wall.

I was crying easily. Exhausted. Irritable. My PMS was out of control. My skin was dry. My mood was all over the place. And I seriously considered going on an antidepressant.

But something in me said: “Pause, take a deeper look.”

So I did what I often encourage my patients to do. I ran functional medicine labs on myself—and what came back was a big red flag: my omega-3 fatty acid levels were bottomed out.

I started supplementing right away, and it was like a light switch flipped. Within a few months my symptoms completely turned around (and honestly, I was feeling better much sooner). No meds—just targeted nutrition.

And going through that personally shifted something in me. I’ve always known food and nutrients are foundational, but this made it real on a whole new level. It reminded me that healing doesn’t have to start with a prescription pad. So often it starts at the cellular level—when we give our bodies the raw materials they need to thrive.

That’s what led us to today’s conversation: essential fatty acids… and a lesser-known one that’s getting a lot of attention lately.

Essential fatty acids 101 (and why “healthy people” can still feel off)

When we say essential, we mean fats your body can’t make on its own. You have to get them through food or supplements.

Most people have heard of:

• ALA (an omega-3)
• LA (an omega-6)

These fats matter for everything from skin health and immune function to mental clarity and emotional resilience.

But here’s the kicker: even if you’re “doing everything right,” you can still feel like something’s missing. That’s where newer research is starting to point toward additional fatty acids that may be more important than we realized.

And one of the most interesting ones is a little-known fat called C15 (pentadecanoic acid).

Meet C15: the “odd-chain” saturated fat with an even stranger origin story

In this episode of the Rethink Aging Podcast, I sat down with Danielle Cole from Fatty15, and we talked about what makes C15 so fascinating.

C15 is an odd-chain saturated fat—and yes, saturated fat has had a bad reputation in conventional circles. But not all saturated fats behave the same way, and Danielle explained that odd-chain fats like C15 may act differently than the “usual suspects.”

She shared that the origin story starts with… dolphins.

Discovering C15: the dolphin story

Danielle described how Dr. Stephanie Van Watson worked with the U.S. Navy on dolphin health. After a fish supply change, the dolphins began developing human-like metabolic issues—things like insulin resistance and fatty liver changes.

The team assumed omega-3s were the problem (after all, dolphins eat fish). But metabolomic testing pointed elsewhere.

According to Danielle, the dolphins weren’t missing omega-3s—they were missing C15, and when C15 was added back in, the dolphins’ issues began resolving within about a month.

It’s a wild story—and it opened the door to asking a bigger question: Could humans be missing this too?

Why would humans be low in C15?

Danielle explained that historically, humans have gotten C15 primarily from full-fat dairy, and that levels may be higher in grass-fed dairy than conventional.

But in modern life:

• Many people avoid dairy (intolerance, preferences, dietary patterns)
• Full-fat dairy has been reduced in many diets
• Farming practices differ
• Even people who eat dairy may not reliably reach “optimal” levels

In other words, you can be living a “healthy lifestyle” and still be low.

And that’s important, because when your cells are missing key building blocks, it can show up in surprising ways—mood, energy, skin, inflammation, metabolic markers, and more.

The core concept: cell membranes need the right fats

One part of our conversation I loved was how Danielle described the cell membrane.

Every cell in your body has a lipid (fatty) layer. And your goal isn’t just “more fat” or “less fat”—it’s the right balance of fats.

She explained it like this:

• Omega-3s (unsaturated fats) help cell membranes stay flexible
• Saturated fats help cell membranes stay stronger and more stable

She also shared that omega-3s, because of their double bonds, can be more vulnerable to oxidative stress—while saturated fats are less vulnerable in that specific way.

Now, to be clear: this is nuanced biochemistry, and you don’t need to memorize it. The takeaway is simply this:

If you’re missing an essential building block, your cells can become more fragile—and your health can reflect that.

“Cellular fragility syndrome”: a newer lens

Danielle and I discussed a term that’s been used to describe low C15 states: cellular fragility syndrome.

She shared that this concept is tied to weakened cell membranes and may be connected to patterns that show up on labs—sometimes even things like shifts in red blood cell markers (like RDW) and iron-related patterns.

This is still an emerging area, and I want to be responsible here: not every fatigue, mood issue, or lab abnormality is caused by one nutrient. But in functional medicine, we always ask: What’s missing? What’s driving this? What’s the root cause?

And the fact that C15 can be measured brings us to a practical question.

Can you test C15 levels?

Yes.

I mentioned that C15 can be tested in the blood, and that I’ve seen it included through Genova Diagnostics in broader fatty acid or nutrient panels. That means you can move beyond guessing and actually get data.

And as always, testing is most powerful when it’s paired with interpretation in the context of your symptoms, history, and goals.

What people report noticing first: mood and sleep

One of the most interesting parts of our conversation was Danielle’s comment that, in their experience, some people notice positive mood and deeper sleep within a couple of weeks.

She attributed this (from her perspective) to a mechanism involving MAO-B inhibition and dopamine support—again, a more technical pathway, but the lived experience is what many people care about first:

Do I feel calmer? More steady? Do I sleep better? Do I have more energy?

She also shared that people often report an energy lift, and referenced mitochondrial support as part of the proposed explanation.

Important note: these are statements shared in an interview context, and research is still evolving. If you’re navigating mood symptoms, insomnia, cognitive decline concerns, or fatigue, please work with a qualified clinician to personalize your plan.

My favorite healthy aging habit from Danielle (and why it matters)

When I asked Danielle about her top healthy aging habit, her answer was beautifully simple:

A morning walk.

She described getting outside early, getting sunlight in her eyes (without sunglasses in the early morning), and using that rhythm to support circadian biology and sleep.

I love this because it’s so aligned with what we teach:
clean air, clean food, clean water, sleep, and sunlight—the basics that move the needle more than most people realize.

Supplements can be helpful, yes. But they work best when they’re layered onto a solid foundation.

So… is C15 the missing piece for you?

Maybe. Maybe not.

But if any of these feel familiar, it’s worth exploring:

• You’re doing a lot “right” but still feel off
• Mood feels more reactive than it used to
• Sleep is lighter, less restorative
• Skin is drier, inflammation is higher, energy is lower
• You avoid dairy (or don’t tolerate it)
• You want to be proactive about brain health and resilience

The most functional medicine answer I can give is:

Don’t guess—test, interpret, and personalize.

Next steps and resources

If you want to go deeper into the science story, we discussed The Longevity Nutrient, and I also encouraged listeners to explore educational resources and Danielle’s background story about the dolphins.

And if you want to stay connected with what we’re doing at Caring for the Body—brain protection, resilience, and aging with purpose—I invite you to join us in the community at caringforthebody.org.

Until next time: be well and be blessed.

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