Carbohydrate During Exercise: How Much and When

Whether to take any

For a run or race that ends inside 90 minutes, eat well beforehand and carry nothing. The one place a little carbohydrate helps is just before a short race or a hard workout: David Roche has runners from high school to pro take at least 20 grams, up to a 30 to 40 gram gel, after the warm-up and openers, in workouts as well as races so the habit holds. Part of why is the signal carbohydrate sends from the mouth: swishing sports drink gave small gains across a 2026 analysis of 90 trials, mostly in men¹.

Past 90 minutes, carbohydrate you take in spares your own stores and keeps blood glucose up, so you can hold your pace longer before fatigue sets in². Take the first gel before you feel empty, at 60 to 75 minutes, and one about every 30 minutes after that. If your stomach is touchy, start with a gel every 35 to 40 minutes and shorten the gap over time.

How much an hour

Start from the range for how long you will be out, then let practice move you up. Grams per gel vary, so read the label and multiply by the gels you take in an hour.

• 90 minutes to about 2.5 hours: 30 to 60 grams an hour. Most runners do well starting near 50 to 60. If you have a history of stomach trouble, start nearer 30 to 40.
• Longer than about 2.5 hours, which includes most marathons: 60 to 90 grams an hour for a road marathon, built up with practice.
• Ultras: Johnson, a sports dietitian for Western States runners, sees most of his athletes race at 70 to 90 grams an hour, the highest near 110 to 115, and holds them lower in heat or at altitude. David Roche says rates above 90 take high output and gut training.

What 120 grams an hour has and has not shown

In eight elite male marathon runners (personal best around 2:23) running two hours, the more carbohydrate they took the more they burned, and their oxygen cost of running was lower at 120 grams an hour than at 60. Moderate or severe stomach symptoms were common at every dose, and nausea, fullness and cramps peaked at 120. Whether it makes a race faster is not yet known, and the authors say gut training should come first³.

Well-trained runners who work up to these rates often say efforts feel easier and they recover faster the next day, which lets them stack more quality in a block. That is a reason to practice, and not yet a reason to expect a faster race. A runner doing 30 miles a week can easily take in more than a session needs, so match the rate to the session: runs under 90 minutes need nothing, and the high rates belong to long runs and hard sessions.

Which sugars

Up to about 60 grams an hour, one sugar, glucose or maltodextrin, is absorbed well. Above that the single-sugar route fills, and a blend of glucose (or maltodextrin) and fructose lets the gut absorb more, because fructose uses a different transporter, as a 2014 review explains⁴. In the 2025 marathoner study the blend changed with the dose: maltodextrin alone at 60, two parts maltodextrin to one of fructose at 90, and equal parts at 120³.

David Roche prefers glucose to fructose at about 1 to 0.8, and notes that 2 to 1 may overwhelm the gut's transporters at very high rates. A position statement also found that premium hydrogel products did no better than standard ones for symptoms⁵. Homemade gels and drink mixes of maltodextrin and fructose hit the same targets at a fraction of the cost, so buy the rate and the form, not a brand.

How to take it

Gels, drinks, chews, solid food and homemade mixes all work. Use the ones you tolerate. Plan the amount per hour, not per bottle, and split the hour into equal feeds every 20 to 30 minutes on a watch alert: at 90 grams an hour that is 30 grams every 20 minutes. Regular windows beat a big dose less often.

What raises the risk of stomach symptoms, in the strongest grade of evidence in a 2025 position statement, is a larger intake volume, a more concentrated carbohydrate solution and a move from liquid to solid, and larger doses taken less often raised it too⁵. Keep drinks dilute as runs get longer: very concentrated bottles are poor hydration and can slow stomach emptying.

Check the number against your own runs

Write down, for every long run, the grams an hour, the form, how your stomach felt and how you felt the next day. Hold each new rate for a couple of weeks of long runs before you step up. A runner who has raced well on 50 grams an hour should not raise it because a review says to, and a runner who handles 100 in training should not cap at 90 because an older table did.

Stomach symptoms are common at every rate, so practice is part of the plan and not a sign you did it wrong. See the guide on training your gut. For the race morning meal, the clock and the plan on paper, see the guide on race-day fueling. For drinks and sodium, see hydration and electrolytes.