f you train for endurance events, you've heard the same carb loading advice on repeat for thirty years. Eat a giant bowl of pasta the night before. Cut carbs first to "trick" your body into storing more later. Don't bother for ultras because you can't store enough glycogen anyway. Most of this is outdated, oversimplified, or just wrong.
So is carb loading a myth? No. Carb loading is real, it works, and it's one of the most well-studied practices in sports nutrition. It might also be the most misrepresented. The version that actually works looks nothing like the advice your high school cross-country coach handed down: it's one to three days of genuinely high carbohydrate intake, around 10 to 12 grams per kilogram of body weight per day, while you taper your training (Burke et al., 2011; Thomas et al., 2016). No depletion phase. No single heroic pasta dinner.
Here are five carb loading myths worth retiring before your next race, with the actual physiology behind why they need to go.
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Join the YDS community on PatreonDoes Carb Loading Actually Work?
Yes, for events longer than about 90 minutes. The research goes back to the 1960s, when Scandinavian researchers showed that a high-carbohydrate diet raised muscle glycogen and dramatically extended how long people could cycle before exhaustion, compared with a low-carbohydrate diet (Bergström et al., 1967). Decades of work since then have refined how to do it, but the core finding has held up: more stored glycogen at the start line means more fuel available before fatigue sets in. For shorter events, normal fueling on the day before is usually enough, and a full load buys you little.
Myth 1: A Big Pasta Dinner the Night Before Is Carb Loading
The pre-race pasta party is a cultural ritual, not a fueling strategy.
A trained endurance athlete stores a few hundred grams of glycogen in muscle and roughly another 100 grams in the liver. Filling those stores to the brim takes time, and it takes a sustained high intake, not one meal. A single pasta dinner adds maybe 100 to 200 grams of carbohydrate to your day. That's not nothing, but it's not "loading." It's just dinner. Let dinner be dinner!
The current guidance for events over 90 minutes is 10 to 12 grams of carbohydrate per kilogram of body weight per day for the 36 to 48 hours before the race, paired with a taper (Burke et al., 2011; Thomas et al., 2016). For a 60-kilogram runner, that's 600 to 720 grams of carbohydrate a day. For comparison, a plate of fettuccine is maybe 100. Cramming one giant plate the night before your marathon will mostly leave you bloated, gassy, and contemplating your life choices at the 4 a.m. start line.
Myth 2: You Need a Depletion Phase Before Carb Loading
The original protocol involved several days of hard training on a low-carb diet to "deplete" glycogen, followed by several days of high-carb refeeding. This idea still floats around the internet like a bad meme. For most athletes it's unnecessary, and frankly counterproductive.
The depletion-then-load model came from early research in which emptying glycogen stores seemed necessary to trigger "supercompensation." But in 1981, Sherman and colleagues showed that trained runners reached similarly high glycogen levels with a far gentler approach: a taper with moderate carbohydrate intake, then three days of high carbohydrate intake, and no depletion phase at all (Sherman et al., 1981). Later work went further. Endurance-trained athletes who ate about 10 g/kg of high-glycemic carbohydrate while resting reached near-maximal muscle glycogen within a single day (Bussau et al., 2002).
The depletion phase adds metabolic stress, makes your last hard workouts feel terrible, increases GI risk, and offers no clear performance benefit for athletes who already train regularly. Skip it. Eat the carbs.
Myth 3: Carb Loading Doesn't Matter for Ultramarathons
This one comes up constantly in ultra circles, and it deserves a careful response. The premise contains a kernel of truth: at hard efforts, you can burn through a large share of your muscle glycogen within the first couple of hours. But the conclusion that carb loading is therefore pointless for a 15-hour event is dead wrong.
Carb loading doesn't exist to fuel hour 12 of your race. It exists to maximize your starting reserves, so you draw from a fuller tank before you lean more heavily on fat and on the carbs you eat during the race (which you should obviously be doing in any event longer than about 90 minutes).
Here's the underappreciated piece of physiology: your gut can only absorb so much carbohydrate per hour. Glucose alone tops out around 60 grams per hour because its intestinal transporter (SGLT1) saturates. You can push that to roughly 90 grams per hour by combining glucose with fructose, which uses a separate transporter (GLUT5) (Jeukendrup, 2014). Some athletes now train their guts to handle more, but there's still a ceiling.
That ceiling matters. At race effort, your working muscles can burn carbohydrate faster than your gut can deliver it. The gap has to come from somewhere, and that somewhere is stored glycogen. Starting with low stores means dipping into that buffer earlier. Starting topped off means more runway before things get hard, which matters most early in the race, when intensity tends to run a little high.
Myth 4: If Zone 2 Burns Fat, Ultrarunners Don't Need Carbs
This is the myth that's spread fastest through endurance running in the last few years, and it confuses two different things. Yes, fat supplies a bigger share of your energy at lower intensities. No, that doesn't mean you're running on fat alone.
In trained men, fat burning peaks at moderate intensity, around 64% of VO2max in one classic study, and at that peak averages roughly 0.6 grams of fat per minute, with a wide range between individuals (Achten & Jeukendrup, 2003). That's somewhere around 300 calories an hour from fat, which doesn't cover the total energy demand of most people at ultra race effort. Carbohydrate fills the gap.
Even dedicated low-carb athletes don't escape this. In a study of elite ultrarunners who'd followed a ketogenic diet for nearly two years, the keto group burned fat at more than twice the peak rate of their high-carb peers. But during a three-hour run, both groups broke down about the same amount of muscle glycogen (Volek et al., 2016). And when elite race walkers switched to a high-fat diet, they burned more fat but became less economical, and their race performance didn't improve the way it did for walkers eating plenty of carbohydrate (Burke et al., 2017). The ratio shifts. The need for carbs doesn't disappear.
There's also your brain, which relies heavily on glucose for fuel (Mergenthaler et al., 2013). At hour 10 of a 100K, cognitive function shapes every decision you make, including the decision to keep moving: navigating the course, timing your fueling, deciding whether that ankle pain is a real injury or just regular ultra suffering. Low blood sugar is one reason your brain can feel like soup at mile 50. A fueled brain makes better calls than an underfueled one.
Myth 5: Carb Loading Is Only for Elite Athletes
Back-of-pack runners get told constantly that fueling protocols don't apply to them because they aren't fast enough to need optimizing. This is nonsense, and you're missing out on real performance gains AS WELL AS PIZZA.
The energy cost of covering a distance on foot is roughly similar whether you run it fast or slow. A 15-hour 100K and a 9-hour 100K burn a comparable total amount of fuel; the slower runner just spreads it over more hours. That means more hours of eating on the move, more cumulative GI stress, and more hours of decision-making on a tired brain. Starting with full glycogen stores helps with all of it. Mid-pack and back-of-pack athletes should arguably take carb loading more seriously, not less.
How to Carb Load Without Giving Up After One Attempt
Here's the pattern we see all the time on the podcast and in Kylee's practice. Someone reads about carb loading. They eat what they think is a lot of carbs for a couple of days. They feel different in their body, the scale moves, and they decide carb loading doesn't work for them. They never checked how many grams they actually ate, what kind, or whether what they noticed was the protocol working as designed.
A few things to know up front.
Expect water weight. It's the point. Glycogen is stored with water, roughly 3 grams of water for every gram of glycogen (Olsson & Saltin, 1970). Load a few hundred extra grams of glycogen and you'll carry an extra kilogram or so of water in your muscles. That's not bloat, and it's not fat. It's fuel and fluid you'll use during the race. The fullness, the slight heaviness, the small movement on the scale: those are signs the protocol is working. If race-week scale numbers aren't useful information for you, this is a fine week to step away from weighing yourself entirely. You don't need that data to execute the plan well.
Know your baseline. Almost nobody eats as many carbs as they think they do. Before deciding carb loading doesn't work for you, track your normal intake for three to five days using whatever tool you tolerate (apps, paper, voice memos). Convert your typical daily carbs to grams per kilogram of body weight. Plenty of endurance athletes who think they "eat a lot of carbs" land well below what a real load requires. Without a baseline, you're loading blind and probably undershooting.
Do a dress rehearsal. Pick a key long run two to four weeks before your goal race and practice the full load in the days leading up to it. Same grams per day, same foods, same timing. You'll learn which carb sources sit well, how much volume you can actually eat, and how your body responds, all in lower-stakes conditions. The first time you try a full carb load should not be the night before a goal race.
Choose easy carbs. White rice, white bread, regular pasta, potatoes, bananas, pretzels, bagels, low-fiber cereals, juice, and sports drinks are the workhorses. Pull back on high-fiber and high-fat foods for those few days. Less fiber gives your gut less to process and lowers the odds of a race-morning bathroom emergency. Spread carbs across every meal and snack instead of back-loading into one dinner. Eight smaller carb-rich snacks go down easier than three giant meals.
Then keep eating. On race morning, eat a carb-forward breakfast 2 to 3 hours before the start, low in fat and fiber. The goal is topped off, not stuffed. And then the part most people still get wrong: keep eating during the race. For events longer than about two and a half hours, the guidance is up to 90 grams of carbohydrate per hour (Burke et al., 2011). Carb loading is the foundation. In-race fueling is the building. (If you're wondering whether you need gels for a shorter race, here's our take on fueling a half marathon. And if the internet has convinced you all those race-day carbs will give you diabetes, they won't.)
The Bottom Line: Is Carb Loading a Myth?
No. Carb loading works for events longer than about 90 minutes. It just isn't the giant pasta dinner of 1985, and it isn't irrelevant for ultras. The current evidence supports 36 to 48 hours (up to about three days) of high carbohydrate intake, around 10 to 12 g/kg/day, paired with a taper, with less fiber and fat while you load. No depletion phase required. It applies to every endurance athlete regardless of pace, and it works best paired with consistent in-race fueling. Track your baseline, expect water weight, practice once before race week, and stop trusting Reddit's metabolic takes.
We talk fueling, carbs, and the myths around both all the time on the Your Diet Sucks podcast. And if you want to run your own numbers past an actual dietitian, the Nutrition Question Thread in the YDS community on Patreon is where Kylee answers exactly this kind of thing, and where "wait, how many grams is that in bagels" gets asked more than you'd think.
References
Achten, J., & Jeukendrup, A. E. (2003). Maximal fat oxidation during exercise in trained men. International Journal of Sports Medicine, 24(8), 603–608. https://doi.org/10.1055/s-2003-43265
Bergström, J., Hermansen, L., Hultman, E., & Saltin, B. (1967). Diet, muscle glycogen and physical performance. Acta Physiologica Scandinavica, 71(2–3), 140–150. https://doi.org/10.1111/j.1748-1716.1967.tb03720.x
Burke, L. M., Hawley, J. A., Wong, S. H. S., & Jeukendrup, A. E. (2011). Carbohydrates for training and competition. Journal of Sports Sciences, 29(Suppl. 1), S17–S27. https://doi.org/10.1080/02640414.2011.585473
Burke, L. M., Ross, M. L., Garvican-Lewis, L. A., Welvaert, M., Heikura, I. A., Forbes, S. G., Mirtschin, J. G., Cato, L. E., Strobel, N., Sharma, A. P., & Hawley, J. A. (2017). Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers. The Journal of Physiology, 595(9), 2785–2807. https://doi.org/10.1113/JP273230
Bussau, V. A., Fairchild, T. J., Rao, A., Steele, P., & Fournier, P. A. (2002). Carbohydrate loading in human muscle: An improved 1 day protocol. European Journal of Applied Physiology, 87(3), 290–295. https://doi.org/10.1007/s00421-002-0621-5
Jeukendrup, A. (2014). A step towards personalized sports nutrition: Carbohydrate intake during exercise. Sports Medicine, 44(Suppl. 1), S25–S33. https://doi.org/10.1007/s40279-014-0148-z
Mergenthaler, P., Lindauer, U., Dienel, G. A., & Meisel, A. (2013). Sugar for the brain: The role of glucose in physiological and pathological brain function. Trends in Neurosciences, 36(10), 587–597. https://doi.org/10.1016/j.tins.2013.07.001
Olsson, K. E., & Saltin, B. (1970). Variation in total body water with muscle glycogen changes in man. Acta Physiologica Scandinavica, 80(1), 11–18. https://doi.org/10.1111/j.1748-1716.1970.tb04764.x
Sherman, W. M., Costill, D. L., Fink, W. J., & Miller, J. M. (1981). Effect of exercise-diet manipulation on muscle glycogen and its subsequent utilization during performance. International Journal of Sports Medicine, 2(2), 114–118. https://doi.org/10.1055/s-2008-1034594
Thomas, D. T., Erdman, K. A., & Burke, L. M. (2016). American College of Sports Medicine joint position statement: Nutrition and athletic performance. Medicine & Science in Sports & Exercise, 48(3), 543–568. https://doi.org/10.1249/MSS.0000000000000852
Volek, J. S., Freidenreich, D. J., Saenz, C., Kunces, L. J., Creighton, B. C., Bartley, J. M., Davitt, P. M., Munoz, C. X., Anderson, J. M., Maresh, C. M., Lee, E. C., Schuenke, M. D., Aerni, G., Kraemer, W. J., & Phinney, S. D. (2016). Metabolic characteristics of keto-adapted ultra-endurance runners. Metabolism, 65(3), 100–110. https://doi.org/10.1016/j.metabol.2015.10.028
