120 g/hr Carbs: The Secret Fuel Strategy of Elite Marathoners or Overhyped Trend?
Estimated read time: 5.4 minutes (about as far into your marathon as it takes to realize you should’ve carb loaded). 😉
Hey Performance Nerds! Jonah here. 🤓
What if the carbs you’re taking in never actually make it to your muscles?
This week is a deep dive for the true nerds. I’ve been talking with PhDs running isotope studies, reviewing the elite data we’re collecting, and digging into the newest research.
Today:
✅ The 5-step journey from gel to performance (most runners fail at Step 3)
✅ Why the 90 g/hr “ceiling” exists — and when breaking it helps
✅ The oxidation vs absorption gap behind mid-race GI blowups
✅ A framework to find your sweet spot (spoiler: it’s probably not what the pros use)
(Augie still thinks bacon is a fueling plan. All confidence, zero science.)
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Stryd — 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.
🧬 The 5 Steps From Gel to Glory (Most Runners Miss Step 3)
Bonking despite crushing gels? That’s because fueling is a five-step relay and most runners drop the baton at Step 3.
Step 1: Intake — What You Swallow
The raw number of carbs per hour. Every gel, drink, chew.
Everyone obsesses over this ("I'm at 90 g/hr!" "I'm pushing 120!").
But here's the truth: swallowing more doesn't mean running faster. Intake just gets you in the game.
Step 2: Tolerance — What Your Gut Holds
How many carbs your stomach handles without revolt.
Running's pounding makes this harder than cycling. You can tolerate high intake without absorbing it. Hello, mile 20 disaster.
Step 3: Absorption — The Real Bottleneck
What actually crosses from gut to bloodstream.
Your intestines have two transporters (think subway turnstiles):
SGLT1 for glucose (~60 g/hr capacity)
GLUT5 for fructose (~30-40 g/hr capacity)
Using both (2:1 or 1:0.8 mixes) opens extra lanes. But there's still a ceiling.
Step 4: Oxidation — What Your Muscles Actually Burn
The performance endpoint: how many grams truly power your run.
Scientists track this with stable isotope tracers—following your carbs until they appear as CO₂ in your breath. Most runners oxidize 60-90 g/hr. Some genetic freaks hit 120+.
Step 5: Utilization — Does It Keep You Fast?
The final boss: do those oxidized carbs maintain your pace?
Carbs deliver 5-7% more ATP per oxygen than fat. At marathon pace, every bit of oxygen is precious. Staying carb-fueled helps you hold speed instead of fading.
Analogy: Carbs are like cars on a highway.
Intake: cars leaving the toll booth
Tolerance: how many lanes the road can handle
Absorption: how many cars get through the gates
Oxidation: how many reach the factory and get turned into energy
Utilization: whether that output wins the race
The 5 Steps Breakdown
Step | 60 g/hr Athlete | 90 g/hr Athlete | 120 g/hr Athlete |
1. Intake | 60 g | 90 g | 120 g |
2. Tolerance | ✓ No issues | ✓ No issues | ⚠️ Needs training |
3. Absorption | 60 g (100%) | 85 g (94%) | 95 g (79%) |
4. Oxidation | 51 g (85%) | 72 g (80%) | 84 g (70%) |
5. Utilization | Baseline | +41% more fuel | +65% more fuel |
📊 Why the 90 g/hr "Ceiling" Is Cracking
The 90 g/hr rule everyone followed? It's breaking.
Now? Athletes are hitting 120+ g/hr. Why?
Better glucose:fructose ratios (1:0.8)
Smarter gut training
New products that actually absorb
But research is mixed. 120 g+ doesn’t guarantee faster times.
What it does do: reduce fat oxidation without sparing glycogen. Athletes can use more than 90 g/hr, but it doesn’t save glycogen — it just shifts fuel toward carbs instead of fat.
In my opinion, that’s the goal in a marathon. Carbs give more energy per oxygen, and the more you burn (vs fat), the more efficient you can be late in the race.
👉 More carbs = more efficiency = stronger finish.
🎯 Who Actually Benefits From >90 g/hr?
Not everyone needs to join the carb arms race. Individual variability is huge.
Two runners, same size. One maxes at 70 g/hr. Another hits 120+. Genetics, gut transporter capacity, and training history all play a role.
Here's the key: Absolute beats relative.
Relative oxidation = % of carb intake you burn
Absolute oxidation = total carb grams you burn
The math:
90 g/hr at 80% efficiency = 72 g oxidized
120 g/hr at 70% efficiency = 84 g oxidized
Lower percentage, but more total carbs.
12 extra grams per hour? Over 2.5 hours, that's a gel of extra energy
✅ Push past 90 g/hr if you:
Race 2:00–2:45 near threshold with sky-high ATP demand
Gut-trained 8+ weeks progressively
Have basics dialed (pacing, training, recovery)
Accept GI risk for 1-2% gains
❌Stay at 60-90 if you:
Race 3:00+ at lower intensities
Have any GI history
Haven't gut-trained systematically
Still working on fundamentals
Those extra grams might be the difference between holding pace and fading in the final 10K.
Or a porta-potty stop.
Choose wisely.
💪 The Durability Secret: Why Carb Oxidation Late Matters Most
What separates elites? They don't fade.
Durability isn't who starts fastest, it's who resists the slowdown at mile 20 when everyone else breaks.
The traditional pattern:
Mile 20 hits → glycogen dips → you shift to fat → economy tanks → you slow
The New Finding:
Higher in-race carb intake (>90 g/hr) may help elites maintain carb oxidation late — when most runners are running on fumes.
Early research (promising) shows runners who keep burning carbs longer:
Slow 2-3% less
Hold better economy under fatigue
Lower perceived effort at the same pace
👉 The real benefit of >90 g/hr isn’t always the extra early fuel.
I think the real edge is still burning a ton of carbs when others can’t. That helps elites hold efficient economy late, a key to durability.
That’s the difference between:
Holding 5:30s vs. shuffling 7:30s.
Passing people at mile 23 who passed you at mile 10.
That’s durability.
It’s not the only factor, but it might be the edge between a PR and another wall.
🗂️ The Verdict
What this means for your running:
90 g/hr remains the reliable sweet spot for most.
>90–120 g/hr may help a subset—only with trained tolerance and proven oxidation.
More ≠ better. Beyond your ceiling, it’s GI roulette.
Durability gains likely come from sustaining carb oxidation late
Personalize, don’t copy pro fueling plans.
Runner Profile | Carb Target | Why |
Most marathoners | 60–90 g/hr | Reliable, well-supported, lower GI risk |
Advanced & gut-trained | 90–120 g/hr | Potential durability gains late in race |
Stage race / multi-day | Stay conservative | Budget carbs across days, avoid depletion |
💬 One last thing before you go.
After the NFL, I wasn’t sure if diving this deep into fueling science still mattered — until I started helping this community.
Your questions about gels, gut training, and race-day fueling brought that fire back.
If you’re second-guessing your carb strategy or just want to share what’s worked (or failed) for you—hit reply. I read every message and I’m here to help however I can.
Fuel smart,
Jonah
Are You a True Running Nerd? Prove it.. 🧐
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.
Why are lifting and plyometrics better for building bone strength than just logging more miles?
- A. They create higher strain rates (forces applied quickly), which bones need to adapt ⚡🦴
- B. Because they last longer and accumulate more total load on bone ⏱️📈
- C. Because they mainly fatigue muscles, and bones get stronger from that 💪➡️🦴
- D. Because they boost hormones like growth hormone and testosterone, which directly drive bone growth 🧬📈
Last Week’s Results: Durability Isn’t Just Miles 🧩🔥
When the wall hits at mile 22, it’s not supplements or “grit” that saves you. Real durability comes from fueling, strength, and marathon-pace work—and most of you nailed it.
The correct answer?
A. Fueling with 50–90g carbs per hour + heavy lifting & plyos + long marathon-pace runs (≥75 min) 🧩🔥 ✅
This combo targets every weak link late in the race: carbs keep glycogen up, heavy/plyo lifts toughen bones and tendons, and marathon-pace blocks harden legs for the exact stress of 26.2.
Here’s how the votes shook out:
🟩 A. Fueling with 50–0g carbs per hour + heavy lifting & plyos + long marathon-pace runs (≥75 min) 🧩🔥 – 231 ✅
⬜️ B. Doing most long runs fasted 🥑🚫 – 1
⬜️ C. Just adding more weekly mileage 📈🏃♂️ – 13
⬜️ D. Focusing on hydration & electrolytes 💧🧂 – 7
Bottom line?
Durability isn’t built on miles alone. Fuel, lift, and rehearse marathon pace until your body stops flinching at it. 🏃♂️🔒
🏃♂️ Stryd Training Tip — Spot Fatigue Before It Stops You
Why do most marathoners fade late? Not just fueling — fatigue quietly changes your mechanics. That’s durability: the ability to hold efficient form through mile 26.
My favorite way to track it outside a lab? With Stryd.
🔑 3 metrics to watch:
Leg Spring Stiffness (LSS): A 10% drop = stride losing “spring.”
Ground Contact Time (GCT): Rising GCT or left–right imbalance = higher energy cost.
Impact Loading Rate: Spikes = mounting fatigue and injury risk.
📊 How to use: Compare runs at the same pace/terrain. Spot dips or spikes early, then adjust training (calf strength, progressive long runs, or recovery) before fatigue wrecks your race.
💡 Bottom line: Without Stryd, these durability metrics stay invisible. With it, you can measure, train, and outlast the fade.