Estimated read time: 5.32 minutes (about as long as reading every fish oil label at the supplement aisle and walking out more confused than you went in 🤔)

Hey Performance Nerds! Jonah here. 🤓

Fish oil is on almost every runner's supplement list. The data has a problem with that pitch.

It probably doesn't move your race times. The recovery and brain story is more interesting.

Here's what you'll learn today:

(Augie eats raw salmon skin when I clean the cutting board. He's set.)

A lot of you replied to last week's email. Most of it was great.

People wanted the deeper paper translation. People shared what they're training for. That meant a lot.

But several replies worried me. Some of you thought this free Thursday newsletter was about to be gated and turned paid.

It's not. Let me say that as plainly as I can.

This free Thursday newsletter stays free. Forever.

The paid membership is a separate thing. It lands on Tuesdays, and it's completely optional.

Reading those replies clarified something for me. I'm fine losing money on Marathon Science.

What I care about is making sure you get the right science. And that you stay connected to the people doing the research.

There is too much hype out there. Too much clickbait. Too many bad tools that just want your money.

I never want to be the barrier between a runner and good science.

I'd rather give the good stuff away than be part of the noise.

So here's what the optional Tuesday membership is.

That's one step of the fueling calculator's setup. The full tool maps your whole race-day plan: carb-loading days, pre-race breakfast, caffeine timing, gut training, and your in-race fueling.

The YouTube series is the part I'm most excited about.

It's where I interview the researchers, travel to them, and build tools alongside them. It's the engine the membership funds.

The pricing is simple, and it never changes.

It's a pay-what-you-want model. $9.99 a month if that's easy for you, and I'll never raise it.

There is a standing 50% off code if $9.99 isn't easy right now. And it's free if you email and ask. No questions, no proof, no awkwardness.

Pay whatever you can. The point is access.

I spent years in the NFL chasing status, money, and standing. I don't want to build anything that way again.

So every dollar the membership makes goes right back out.

The goal is simple. Build the biggest, best-supported community for real science and better tools.

Not a business that stands between you and it.

If any of this raises a question, hit reply. I read every message, and I will answer you myself. Your replies are how I decide what to build next.

Which brings me to today. Fish oil is a textbook case of marketing overselling a supplement.

Cutting through that hype is the whole job. Let's get into it.

The gel I race with (and why):

BETA FUEL: delivers 40g of carbs per serving through a 1:0.8 maltodextrin-to-fructose ratio.

That ratio is why I've never had a GI issue with it in 3 years of racing. Fast absorption, no gut bombs. I don't earn a commission on this. I negotiated 15% off for you because I believe in the science behind it.

Marathon Science subscribers get 15% off one-time purchases with code JONAH26. Live now through May 31.

The running power meter trusted by serious athletes — is now an official performance sponsor of Marathon Science, delivering real-time pacing precision so you can train smarter and race faster.

💡 See this week’s full Stryd training tip at the end of this newsletter.

Fish oil is a special kind of fat. Your body builds it into the outer wall of every cell.

That matters most for the cells doing the most work: heart, brain, and working muscle.

Think of it like rigid versus flexible building material. Cells built with EPA and DHA (fish oil) flex under load and recover faster from damage.

Two of these fats matter: EPA and DHA. You get them from oily fish like salmon, sardines, mackerel, anchovies, and herring.

Algae oil delivers the same EPA and DHA for runners who skip fish.

The plant version, ALA from flax and chia, doesn't exactly count. Your body converts ALA into EPA so badly that almost none gets through.

One lab number tells how much EPA and DHA you've built into your cells. It's called the omega-3 index.

The general health target is ≥8%. Most runners sit at 4-6%.

Race performance is the first place the marketing falls apart.

Lewis and colleagues' 2020 systematic review pulled together 32 athlete trials. No consistent improvement in time-trial performance, race times, or maximal strength.

Blannin and colleagues' 2025 trial ran three arms in 55 trained male amateurs. EPA-rich oil, DHA-rich algae oil, and a coconut placebo.

All three groups improved their 24 km time-trial equally.

That's training talking, not omega-3.

Strength and power? Minimal effect at any dose.

Better physiology and recovery markers don't automatically translate to a faster clock.

That's the line most fish oil brands won't say out loud.

Blannin 2025 measured heart rate and perceived effort at fixed easy-to-moderate cycling workloads.

Across both treatment groups:

Mechanism: once EPA and DHA integrate into membranes, your cardiac and vascular response to submax demand shifts.

Easy pace may feel easier at the same heart rate.

Likely shows on a steady-state Sunday run, not on a race clock.

Tsuchiya and colleagues' 2020 meta-analysis pooled 10 RCTs on muscle damage.

Day-after soreness dropped meaningfully at 24 hours. By 48 hours the effect was barely meaningful on a 0-10 soreness scale.

A 2026 meta-analysis of 41 athlete trials confirmed it. Omega-3 lowers the spike in inflammation and muscle-damage markers (IL-6, TNF-alpha, CRP, creatine kinase) after hard sessions.

Effects are stronger at ≥2 g/day for ≥6 weeks, and stronger in recreational athletes than elites.

Mechanism: EPA and DHA convert into cleanup molecules that shut down inflammation after damage.

Your body has a built-in cleanup crew. Omega-3 hands it better tools.

Higher-dose DHA may protect nerve fibers from damage in collision-sport athletes. Small trials, mostly football and rugby.

For runners, this is a long-term brain bet, not a training-week lever.

If recovery markers improve at 2-3 g/day after 4-6 weeks, can you absorb slightly more training before breakdown?

Sleep, carb availability, and training structure dominate this lever by a wide margin. A runner sleeping 6 hours and undereating carbs has bigger levers to pull before adding a pill.

Personal note: I take SiS fish oil daily. The downside is near-zero, and the long-term brain and recovery case is rationale enough.

I would never tell you it's making me faster. Carbs and sleep do more.

Dose: 2-3 g/day combined EPA+DHA, split across 2-3 doses with meals.

Duration: 4-6 weeks for HR and RPE shifts to show up. 8-12 weeks for your omega-3 index to move meaningfully.

Form: Triglyceride (TG) or re-esterified TG beats ethyl ester for absorption.

Quality: Third-party tested (IFOS or equivalent). Oxidation and label inaccuracy are common.

Food-first option: Two portions of oily fish a week matches several RCT doses, without purity concerns.

Optional biomarker: Test your omega-3 index at week 0 and week 12. Trębacz showed runners can move from roughly 6% to 12%. If yours doesn't budge, the supplement may not be doing its job.

Bottom line: Fish oil earns a niche slot: plant-based runners, heavy-eccentric blocks, long-term brain-health bets. Not the default slot most marketing pretends.

Jonah

Welcome to the prove you’re a nerd section. Each week, I ask a question about a common running science myth.

Answer correctly, and you’ll be entered into a weekly raffle to win a package of Jonah’s favorite supplements.

Fiber is one of the best things you can eat for long-term health, blood sugar control, and even recovery. But 26.2 miles at marathon pace? Different story 😅

The correct answer?
A. Fiber slows digestion and gastric emptying, which can increase bloating and GI distress during hard running 🚽🏃‍♂️ ✅

Fiber deliberately slows digestion. Normally, that’s a huge win because it helps stabilize energy and keeps you fuller longer. But before a race, slower digestion means more food and fluid hanging around in the gut while blood flow is being redirected to working muscles.

That’s basically the perfect setup for bloating, cramps, and emergency porta-potty decisions at mile 8.

Here’s how the votes shook out:
🟩 A. Fiber slows digestion and gastric emptying, which can increase bloating and GI distress during hard running 🚽🏃‍♂️ – 351 ✅
⬜️ B. Fiber prevents your body from storing glycogen before the race 🚫🍝 – 14
⬜️ C. Fiber causes your muscles to absorb less oxygen during exercise 🫁❌ – 2
⬜️ D. Fiber turns carbohydrates into fat instead of usable running fuel 🥑⚡ – 2

Most of you absolutely nailed this one.

There’s one trick worth knowing though: low-fiber before racing does not mean low-fiber all the time. Chronic high-fiber diets are still strongly linked to better health, better microbiome diversity, and improved metabolic function.

The key is timing.

Elite marathoners often reduce fiber only in the final 24–48 hours before a race to lower gut residue and minimize GI risk while still maximizing carb intake.

Bottom line?
Fiber is your friend during training blocks. Just maybe not at 5 a.m. on race morning before six gels and a marathon pace start.

Today's piece lands on a familiar truth: supplements are a small recovery lever. Training structure is the big one.

Here's how I make that big lever visible. I use Stryd's Running Stress Score (RSS), my favorite load score that tracks how much I actually trained.

Zoom out first. My 42-day rolling RSS average climbed from near 0 to about 175 across the 90-day window.

That rise is the macro periodization story. I built capacity gradually, week over week, instead of stacking load too fast.

The slow climb is the proof I didn't shock the system.

Now zoom in. Within those same weeks, peak days hit roughly 500 RSS while the day after dropped to about 50.

That gap is the micro periodization story. The low days are not wasted time.

They're what lets me hit quality on the next hard session.

Both scales matter together. The macro climb proves I added load safely; the micro spike-then-recover proves my easy days actually recover me.

Pull your own 90-day RSS chart in PowerCenter this week. Check two things: is your rolling average climbing smoothly instead of spiking?

And within your weeks, do your hard days have real low days after them?

Periodization beats any pill, and RSS lets you watch it operating at both scales.

👉 Try it on your next run