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Carbs for long endurance: what an amateur can borrow from elite fueling strategies

The elite load up to 120 grams of carbs per hour. We break down how much fuel you really need for long races, why glucose and fructose are worth mixing, and how to train your gut to handle it.

DV
Dmitry Volkov

Gels, sports drinks, chewable carb candies — the arsenal on the aid-station tables of elite marathoners and triathletes grows with every season. Today's top ultramarathoners load up to 120 grams of carbs per hour — a number that just ten years ago looked like a straight road to a stomach upset. What drives the trend isn't fashion but physiology: the more fuel you can absorb, the longer you hold your pace. Let's figure out what from the elite playbook actually works for an amateur, and what is better left to the pros.

How many carbs, and when

The right amount depends on how long the race is, not on your competitive level:

  • Up to 60 minutes — you barely need fuel; a mouth rinse with a carb drink is enough: receptors in the mouth "trick" the brain and lower the sense of effort.
  • 60–150 minutes — 30–60 g/h.
  • Longer than 150 minutes — 60–90 g/h.

Those 120 g/h are an ultramarathon story: reviews note that such a dose delays the onset of fatigue over ultra-long distances. But for races longer than 150 minutes, going above 90 g/h usually brings no added benefit — unless glycogen is completely depleted.

The amateur's paradox is that the typical mistake isn't overeating but under-fueling. Many people eat a single gel during a three-hour race and then wonder about the "wall" at the finish.

Two transporters: why a blend absorbs better

The gut moves glucose via the SGLT1 protein, and its throughput is limited: pure glucose is oxidized at a rate of 1.0–1.2 g/min (about 60 g/h) — that's the "ceiling." But fructose has its own channel — GLUT5. Add it in, and the total oxidation rate climbs to roughly 1.5 g/min — the very same ~90 g/h.

Hence the fashion for blends. The classic glucose-to-fructose ratio is 2:1, and some studies suggest closer to 1:0.8 for better tolerance. During exercise the advice is a 6% glucose solution or an 8–10% glucose-fructose blend. The form — gel, drink, or chew — is a matter of convenience: what matters is that it gets absorbed, not the texture.

The practical takeaway: read the ingredients. If you want to absorb more than 60 g/h, look for both maltodextrin/glucose and fructose on the label, not a single source.

A trained gut is a skill

The stomach, like muscles, responds to training. Taking carbs regularly during workouts "tunes" the GI tract: the activity of those very SGLT1 and GLUT5 transporters rises, absorptive capacity grows, and the risk of distress drops.

A review cites a telling protocol: 10 sessions over two weeks, running at 60% of VO2max for 60 minutes with a gel of 30 g of carbs at minutes 0, 20, and 40. The result — a marked reduction in gastrointestinal discomfort.

The main mistake is testing new nutrition on race day. A "race" stomach is prepped in advance, with the same gels and the same routine you plan to use on the course.

How to put it into practice

Let's pull it together into a plan for a long race (longer than 150 minutes):

  1. Loading. For events longer than 90 minutes — 10–12 g/kg of carbs per day, starting 36–48 h before the start. The last meal — no more than 75 g of carbs and at least 2 h before you head out.
  2. On the course. Start with 60 g/h from a glucose-fructose blend; if your GI tract is trained — move toward 90 g/h. Don't forget sodium (30–50 mmol/L in the drink aids absorption) and caffeine (6–9 mg/kg 60 minutes before the start), if it suits you.
  3. Recovery. The first 4 hours — 1–1.2 g/kg/h, for a daily total of 8–10 g/kg to restore glycogen.

And most importantly — rehearse the whole plan on long training runs, not on race day.

Key points

  • Fuel amounts are set by duration: up to 60 min — mouth rinse, 60–150 min — 30–60 g/h, longer — 60–90 g/h.
  • 120 g/h is an elite-ultramarathon story; a solid 60 g/h is enough for most amateurs.
  • A glucose-fructose blend (2:1 or ~1:0.8) raises oxidation from ~1.0–1.2 to ~1.5 g/min — that's the key to high doses.
  • The gut is trainable: regular carbs during workouts improve tolerance.
  • The amateur's mistakes are under-fueling on carbs and trying new nutrition on race day.

Source: Cao W., He Y., Fu R., Chen Y., Yu J., He Z. — Carbohydrate Supplementation Approaches, Nutrients, 2025. https://www.mdpi.com/2072-6643/17/5/918

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