Carb Loading for Training, Not Just Race Day

• Key Takeaways
• Recovery Is Where Training Fuel Does Its Work
• Carb Loading for Training Is a Weekly Tool, Not a Race-Week Ritual
• Most GI Trouble Traces Back to a Few Foods
• Building Carb Loading for Training Into the Week
• Fuel Belongs on the Same List as Load
• Suggested References

You plan and periodize load down to the session. You know the difference between a threshold day and an easy day, and you know why the easy day has to stay easy. Then the athlete’s nutrition gets treated like a switch that flips on during race week.

Carb loading for training is the piece that often falls through that gap. Consider an athlete three weeks into a heavy build. Her sessions look right on paper, but her power on the second hard day of the week keeps sliding and her long-run pace drifts by the final hour. More often than not, the cause is fuel. If she is recovering with a carbohydrate deficit, each quality day starts a little emptier than the last.

This article looks at fueling for endurance training as a daily driver of adaptation, not a race-week ritual. We will cover why training fuel matters for recovery, how to use carb loading across a training week, where GI issues come from and how low-FODMAP fueling helps, and how to build all of it into a plan you already run.

Recovery Is Where Training Fuel Does Its Work

Training fuel matters because adaptation happens during recovery, and recovery runs on carbohydrates. When an athlete finishes a hard session, muscle glycogen sits depleted. The body refills those stores over the next day or two, and the speed of that refill sets how strong the next quality session feels. Under-fuel the recovery, and the next hard day starts on a lower tank.

That refill is not instant. With enough carbohydrate, muscle glycogen returns to pre-exercise levels within about 24 hours; with too little, you are at the start of a fuel deficit. In a 2022 study using magnetic resonance spectroscopy, Namma-Motonaga and colleagues tracked endurance athletes across a full day of recovery. Intakes of 7 and 10 grams of carbohydrate per kilogram of body mass restored muscle glycogen within 24 hours, while 5 grams per kilogram fell short. For an athlete running two key sessions 48 hours apart, that window decides how session two goes. Fuel it well, and session two lands at full quality. Fuel it poorly, and the numbers slide.

Researchers have a useful phrase for this: fuel for the work required. Impey and colleagues (2018) framed carbohydrate availability around the demands of each session rather than a flat daily target. In practice, that means the carbohydrate around a hard day should rise to meet it, while the day after should support the repair still underway. A coach who thinks this way stops seeing nutrition as a background constant and starts treating it as another variable to program.

Here is where it compounds. A single under-fueled day is recoverable. Three weeks of them, stacked across a build, are what turn a promising block into a plateau. The athlete feels fine on the easy days, so nothing seems wrong. The cost shows up only on the days that matter, when the legs will not produce the power the training called for. Fuel recovery well across the block, and the hard days show up at full quality instead of feeling flat.

Carb Loading for Training Is a Weekly Tool, Not a Race-Week Ritual

Carb loading has a race-week reputation. The classic image is the night-before pasta dinner, a one-time top-off before the start line. That version is real, yet it is the narrowest use of the idea.

The athlete training ten to fifteen hours a week faces a version of the same demand every week, not once a season. A back-to-back weekend of a long ride Saturday and a long run Sunday asks nearly as much of glycogen stores as some races do. If Saturday empties the tank and Sunday starts before it refills, Sunday is compromised before the athlete laces up.

For these athletes, carb loading for training means raising carbohydrate intake in the day or two ahead of the heaviest sessions, not only before events. Take a masters athlete building for a spring marathon. Her peak weeks include a Thursday threshold session and a Saturday long run with quality in the final third. Loading carbohydrate on Wednesday and Friday, rather than eating the same amount every day, gives both sessions a full tank. The flat-intake version leaves Saturday underpowered, and the quality miles at the end, the ones that matter most, are the first to suffer.

Coaching tip: On weeks with back-to-back key sessions, cue the athlete to raise carbohydrate intake the day before each one, not just the night before a race. The Friday plate matters as much as the Saturday session.

This is not about eating more all the time. Instead, it is about matching intake to the week’s shape. Lighter days can run leaner. The days that carry the load get the fuel that lets the athlete actually complete the work as prescribed.

Most GI Trouble Traces Back to a Few Foods

Ask a room of endurance athletes about race-day stomach problems and most hands go up. The trigger is often not the effort itself. Instead, it is what went in during the hours and days before, and a large share of it comes down to a specific group of carbohydrates.

Those carbohydrates are called FODMAPs, short for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. They are poorly absorbed in the small intestine, so they draw in water and ferment in the gut. At rest, most people handle them fine. Hard endurance work is different. During prolonged intense exercise, blood is diverted away from the gut toward the working muscles, and Costa and colleagues (2017) describe how that drop in gut blood flow, along with the mechanical stress of hard training, compromises how the gut works. Add a heavy FODMAP load on top, and the cramping, bloating, and worse follow.

A low-FODMAP approach in the days before key sessions and races eases those symptoms. The useful part for a coach is that it rarely requires a full diet overhaul. It is mostly a set of swaps. For example, maple syrup replaces honey. A high-FODMAP energy bar trades for a lower-FODMAP option. Onion and garlic get eased back the day before a long effort. Small changes, and yet they can be the difference between an athlete who finishes strong and one who spends the last hour managing their gut instead of their pace.

Our fueling partner NooMinds put together a low-FODMAP fueling guide that lays out these swaps for endurance athletes. It is a practical starting point for any athlete whose training keeps getting interrupted by GI issues.

Building Carb Loading for Training Into the Week

None of this works as a separate nutrition project bolted onto training. It works when it lives inside the plan the athlete already follows. The simplest way is to map carbohydrate emphasis onto the week you have already built during base training and the blocks that follow.

Look at where the hard days fall. Raise carbohydrate the day before each one and on the day itself. Let the genuine easy days run a little leaner. As a result, the fueling follows the training instead of working against it. 

Sample training week showing how carb loading for training maps onto key sessions.

The table is an illustration, not a prescription. The amounts depend on body size, session length, and the athlete’s own tolerance, which is why the day-before-a-long-effort meals are worth rehearsing in training rather than testing for the first time on race week.

Two habits make this stick. First, treat the pre-session meal as part of the session, planned with the same care as the workout itself. Second, log how the gut felt alongside how the legs felt, so patterns show up over a block instead of staying anecdotal. An athlete who notes that a particular pre-long-run breakfast sits badly has just handed the coach a fix worth more than another interval.

Fuel Belongs on the Same List as Load

Coaches already track load, intensity, and recovery. Fuel belongs on that same list. It is not a separate discipline so much as another input into the same goal, getting the athlete to the next quality session ready to work.

Start small. Pick the two hardest days in an athlete’s week and get the carbohydrate right around them. Then watch what happens to the quality at the end of the long sessions. The change is usually visible within a single block.

If you want ready-made tools, the NooMinds low-FODMAP fueling guide and its NooCoach Hub, which includes a carb calculator built for training, not just race day, are good places to start to get your fueling on par with your training demands.

Good fueling follows good structure. Build your athletes’ training weeks in EndoGusto, see the key sessions at a glance, so you know which days to fuel around. 

Suggested References

• Namma-Motonaga, K., Kondo, E., Osawa, T., Shiose, K., Kamei, A., Taguchi, M., & Takahashi, H. (2022). Effect of Different Carbohydrate Intakes within 24 Hours after Glycogen Depletion on Muscle Glycogen Recovery in Japanese Endurance Athletes. Nutrients, 14(7), 1320. https://doi.org/10.3390/nu14071320
• Impey, S.G., Hearris, M.A., Hammond, K.M., Bartlett, J.D., Louis, J., Close, G.L., & Morton, J.P. (2018). Fuel for the Work Required: A Theoretical Framework for Carbohydrate Periodization and the Glycogen Threshold Hypothesis. Sports Medicine, 48(5), 1031–1048. https://doi.org/10.1007/s40279-018-0867-7
• Costa, R.J.S., Snipe, R.M.J., Kitic, C.M., & Gibson, P.R. (2017). Systematic review: exercise-induced gastrointestinal syndrome, implications for health and intestinal disease. Alimentary Pharmacology & Therapeutics, 46(3), 246–265. https://doi.org/10.1111/apt.14157
• Gaskell, S.K., Taylor, B., Muir, J., & Costa, R.J.S. (2020). Impact of 24-h high and low fermentable oligo-, di-, monosaccharide, and polyol diets on markers of exercise-induced gastrointestinal syndrome in response to exertional heat stress. Applied Physiology, Nutrition, and Metabolism, 45(6), 569–580. https://doi.org/10.1139/apnm-2019-0187