Why 120 g/h Carb Intake Works - And What It Means for Triathletes, Cyclists and Runners

For years, endurance fueling guidelines have stayed conservative: “60–90 g of carbs per hour.” But a new study on elite marathoners, paired with expert commentary on the Science of Sport podcast, suggests we may be under-fueling - especially in high-intensity endurance events like marathons, long rides, 70.3, and full-distance Ironman.

This article breaks down what the science really shows, why carb ratios matter, and how athletes can apply this safely.

The New Study: What They Actually Tested

Ravikanti et al., 2025: ¹³C-labelled glucose-fructose oxidation in elite marathoners

Research paper: Journal of Applied Physiology - Ravikanti et al. 2025

Eight elite male marathoners (average marathon time ~2:22:54) ran at marathon pace while consuming three different carbohydrate intakes.

The Three Fueling Conditions (with exact ratios)

This 1:1 ratio is what allows the gut to transport very high amounts of carbohydrate per hour. It is the same dual-pathway principle MetriqFuel products are designed around.

Finding 1: More Carbs = More Usable Energy

Exogenous carbohydrate oxidation increased as intake rose:

• 60 g/h - about 0.89 g/min
• 90 g/h - about 1.31 g/min
• 120 g/h - about 1.68 g/min (during the second hour)

Some individuals reached peaks around 1.64–1.99 g/min, which are among the highest values ever recorded in a running study.

Finding 2: 120 g/h Improved Running Economy

Compared to 60 g/h, 120 g/h reduced oxygen cost by roughly 2.6 percent. That means runners used less oxygen at the same pace, which is a real metabolic advantage over the marathon distance.

Finding 3: Only 120 g/h Prevented the Shift to Fat Metabolism

During the second hour of running, the contribution from carbohydrate was:

• 60 g/h - about 46 percent carbs, 54 percent fat
• 90 g/h - about 51 percent carbs, 49 percent fat
• 120 g/h - about 66 percent carbs (no major shift toward fat)

Why this matters: at race intensity - marathon pace, high tempo running, strong riding, 70.3 and Ironman race power - relying more on fat makes the effort feel harder and less efficient. Staying more carb-dependent helps you hold higher speeds for longer.

Finding 4: The Limiting Factor Is The Gut

The big downside is gastrointestinal distress. At all doses, athletes experienced some GI symptoms, but 120 g/h was clearly the worst:

• Higher rates of nausea
• More stomach fullness
• More abdominal cramps
• All runners reported moderate to severe stomach fullness at each intake level

It is important to note that the study used fluid only, and at very high concentrations: 12 percent, 18 percent, and 24 percent carbohydrate solutions. That is a tough format for the gut to tolerate, especially while running.

In the real world, most runners, cyclists and triathletes will spread intake across drinks, gels, chews and sometimes solids, which usually feels much easier on the stomach.

What The Podcast Adds (Science of Sport)

The Science of Sport podcast did a deep dive on this study and the bigger picture around high carbohydrate intake:

• Apple Podcasts: A deeper insider look at fatigue and pacing - why high carbohydrate intake works
• Spotify: A deeper insider look at fatigue and pacing - why high carbohydrate intake works

Key points from their discussion:

• High carbohydrate intake works not just because of glycogen, but because it helps with pacing, neuromuscular control and central fatigue.
• For elite runners, cyclists and triathletes, traditional 60–90 g/h may be lower than ideal if the goal is maximal performance.
• The GI system is trainable, but you have to train it gradually, just like your muscles and cardiovascular system.
• There is strong metabolic evidence, but we still need more full performance trials at 120 g/h.

Why This Matters For Running, Cycling and Triathlon

Running

Running places a lot of mechanical stress on the gut. Higher carb intakes are harder to tolerate when everything is bouncing. Moderate concentrations, spreading intake between gels and drinks, and proper gut training are essential if you want to push above 90 g/h.

Cycling

Cycling is where very high carbohydrate intakes are most realistic. You are more stable, digestion is easier, and you can take on more volume. This is why many professional cyclists now fuel at 100–130 g/h during key race phases.

Triathlon, 70.3 and Full Ironman

In long-course triathlon, the bike leg is your main fueling window. You can push closer to the 90–120 g/h range on the bike, then slightly lower intake on the run where GI stress is higher.

As a practical guide:

• Bike leg - around 90–120+ g/h if you have trained for it
• Run leg - around 60–90+ g/h, adjusted for individual tolerance

Why The Carb Ratio Matters (And Where MetriqFuel Fits In)

The highest performing condition in the study used a 1:1 glucose:fructose ratio at 120 g/h.

MetriqFuel PRO is the only product on the market with this golden 1:1 Ratio

Your body absorbs carbs through two main transporters in the gut:

• SGLT1 - transports glucose and glucose polymers (like maltodextrin), topping out around 60 g/h
• GLUT5 - transports fructose, and can add another 30–60 g/h on top of that

By using both pathways with a glucose plus fructose blend, you can push total intake toward 100–120 g/h without overwhelming a single transporter. This is the same dual-pathway fueling principle behind MetriqFuel formulations.

In other words, this study directly supports the idea that for very high carb intakes, you should use a glucose:fructose mix, not glucose alone.

Practical Guidelines - How To Use This As An Athlete

1. Start Where You Are

If you currently take in 40–60 g/h, do not jump straight to 120 g/h. That is a fast track to GI issues.

2. Build Gut Training Into Your Week

Use long runs, long rides and race-pace sessions to gradually increase carb intake. Progress something like:

• 60 g/h → 75 g/h → 90 g/h → 100–110 g/h → 120 g/h (if you tolerate each step)

3. Mix Formats

Use a combination of drink mix, gels, chews and maybe small solid snacks on the bike. Avoid relying only on very strong drinks.

4. Target Ranges By Sport

• Running: 60–90 g/h for most, slightly higher only if well trained and tolerant.
• Cycling: 90–120 g/h, especially in long or high-intensity rides.
• 70.3 and Ironman: 90–120 g/h on the bike, then 50–80 g/h on the run as tolerated.

5. Use A 1:1 Glucose:Fructose Blend For 100–120 g/h Strategies

This matches the research, and it is the most efficient way to actually absorb very high carbohydrate intakes without overloading the gut.

Bottom Line

The Ravikanti et al. 2025 study and the Science of Sport discussion both point to the same idea:

120 g/h of carbohydrate, using a 1:1 glucose:fructose blend, offers clear metabolic advantages for performance - but only if your gut is prepared for it.

For most runners, cyclists and triathletes, a realistic goal is to work towards 90–110 g/h with smart product choices and a structured gut training approach.

For elites or athletes chasing big results in marathons, 70.3 and full Ironman, 120 g/h can be a powerful tool - but it has to be practiced, not guessed on race day.

With a dual-pathway fueling system like MetriqFuel, you are already aligned with the same physiology that made this study so interesting. The next step is to personalise your intake, train your gut, and match your fueling strategy to the demands of your race.

We are of the strong belief that fueling a middle and full distance triathlon needs a combination of different ratios for you to perform to your peak and needs to be practised at race intensity and gut trained to be able to fuel at these high rates. 

Hear from Daniel about his mixed ratio fueling strategy below

Get your MetriqFuel Bundle With A Mixture Of PRO 1:1 and PURE 2:1 so you can level up your fuelling and performance.

MetriqFuel Bundle Deal