Should Endurance Athletes Still Carb Load? What the Research Says (and What the Pasta Party Gets Wrong)

Last week I told a client her carb load target for the day before her race: 834 grams of carbohydrate. One day. She stared at me on Zoom for a solid three seconds before asking if I had accidentally added a digit.

I get that reaction almost every race season, and I understand it. Somewhere between the 1960s and your local running club, “carb loading” got translated into “eat a big bowl of pasta the night before.” That is not carb loading. That is dinner.

So let’s talk about what carb loading actually is, whether it still works, who it works for, and the four myths I find myself busting on client calls every single week.

Where carb loading came from (two Swedish scientists and a lot of needles)

In 1966, Jonas Bergström and Eric Hultman ran one of my favorite experiments in sports science history, on themselves. Each of them pedaled one leg to exhaustion while the other leg rested, then they ate a high carbohydrate diet and took repeated muscle biopsies from both legs (Bergström and Hultman, 1966). The exercised leg did not just refill its glycogen, it supercompensated to roughly double the normal level. The rested leg barely changed.

A year later, the same group showed that cyclists eating a high carbohydrate diet after depletion could nearly triple their muscle glycogen, and that time to exhaustion tracked right along with how much glycogen they started with (Bergström et al., 1967). Worth noting: that study was 9 healthy men on cycle ergometers, which describes a lot of the classic literature in this field, and we will come back to that when we talk about female athletes.

That research spawned the classic 7 day protocol some of you may have heard from an older coach: a brutal depletion run, then three or four days of almost no carbs, then three or four days of loading.

Myth 1: You need a depletion phase

This one was put to bed in 1981 and somehow still shows up in my inbox.

Sherman and colleagues compared the classic depletion protocol against a simple version: just taper your training and eat high carb for the final three days. Muscle glycogen came out virtually identical, 207 versus 203 mmol/kg, and race performance over 20.9 km did not differ (Sherman et al., 1981). The depletion week added nothing except fatigue, irritability, and a miserable week of training on empty legs.

Applicability caveat: that study was trained male runners. But this is one of the most consistent findings in the field, and no modern guideline recommends a depletion phase for anyone (Burke et al., 2011).

What a real carb load looks like in 2026

The current consensus guidelines, led by researchers like Louise Burke (whose work I trust about as much as anyone’s in this field), are clear:

• For events longer than about 90 minutes: 10 to 12 g of carbohydrate per kg of body weight per day, for 36 to 48 hours before the race (Burke et al., 2011; Thomas et al., 2016).
• For events under about 90 minutes: you do not need a formal load. Normal daily fueling of roughly 7 to 12 g/kg in the final 24 hours covers you (Thomas et al., 2016).

Run the math and you will see why my client thought I mistyped. For a 70 kg athlete, 10 g/kg is 700 grams of carbohydrate in a day. That is roughly nine cups of cooked rice plus juice, pretzels, bananas, and a bagel or two. It is a genuine eating project.

There is also a legitimate one day version. Bussau and colleagues had endurance trained men eat 10 g/kg of high glycemic carbs for one day while resting, and muscle glycogen nearly doubled in 24 hours, from 95 to 180 mmol/kg, with no further gain by day three (Bussau et al., 2002). Small study, 8 trained men, fully inactive that day, so if your race week includes real training sessions, the 2 to 3 day version gives you more margin for error.

In my practice we use both. Right now I have gravel and ultra athletes running 3 day loads at around 445 g/day minimum with the biggest day front loaded early, and athletes who hate feeling full for days doing a single day load in the 670 to 834 gram range, a lot of it from liquids. One client tried the one day version specifically because three days of high volume eating left her feeling puffy, and for her the single big day was mentally much easier. That is the kind of individual detail no guideline will give you, and it is exactly what race week rehearsals are for.

Myth 2: The pasta party covers it

A plate of pasta is 80 to 100 grams of carbohydrate. If your target is 700, the pre race dinner is a rounding error, roughly 15 percent of the job. Field research backs this up: when scientists have measured what athletes actually eat during “carb loading,” many never get anywhere near the intakes needed to maximize glycogen (Burke et al., 2011).

And there is a second problem with outsourcing your load to one dinner: your liver. Liver glycogen, which defends your blood sugar while you race, drains substantially overnight even if you ate well the evening before (Gonzalez et al., 2016). A recent review by Podlogar and Wallis found no clear evidence that the liver can be supercompensated in advance the way muscle can (Podlogar and Wallis, 2022). Translation: race morning breakfast is not optional. The pasta party plus a carb rich breakfast 2 to 4 hours before the gun is how the whole system gets topped up.

Myth 3: Everyone should carb load for every race

Carb loading is event specific, and the research on this is older and stronger than most people realize.

For events over 90 minutes, elevated starting glycogen postpones fatigue by around 20 percent in time to exhaustion tests and improves real world performance by roughly 2 to 3 percent (Hawley et al., 1997). At marathon pace, 2 to 3 percent is minutes.

Under 90 minutes? Sherman’s runners saw zero performance benefit at 20.9 km even with supercompensated glycogen (Sherman et al., 1981). You simply do not run out of fuel in a well fed hour of racing.

And here is my favorite complication. Burke’s group ran the first placebo controlled carb loading trial: well trained male cyclists, 100 km time trial, properly fueled during the ride. The loaded group started with significantly more glycogen and finished no faster (Burke et al., 2000). When you fuel well during a 2.5 hour race, pre race loading matters less than the textbooks implied. Caveats: 7 trained men, and longer or hillier events with less in race fueling opportunity (hello, gravel racing) are a different story. But it is a useful corrective to the idea that loading is magic rather than one lever among several.

Myth 4: Carbs will make you heavy and bloated on race day

Two different fears here, so let’s take them separately.

The scale fear is real but misread. Every gram of glycogen is stored with roughly 3 grams of water (Olsson and Saltin, 1970; confirmed experimentally by Fernández-Elías et al., 2015, in 9 trained men rehydrating after cycling in the heat). A full load adds roughly 1 to 2 kg of scale weight. That weight is fuel plus a built in hydration reserve that you will be very glad to have at hour four. When my athletes see the scale jump 1.5 kg the morning before a race, that is confirmation the load worked, not a problem to fix. I have this conversation weekly, because day to day weight swings from water, sodium, and carb intake spook athletes who are watching the scale during race week.

The bloat fear is legitimate and manageable. Three fixes from both the literature and my client roster:

1. Go lower fiber and lower FODMAP for the load window. Lis, Stellingwerff and colleagues showed a low FODMAP approach meaningfully reduced GI symptoms in runners in just six days (Lis et al., 2018). That was 11 recreationally competitive runners, 5 men and 6 women, and short term, but it matches what I see in practice constantly. White rice, potatoes, bananas, maple syrup, rice cereal, and sourdough do the job without the fermentable load of huge whole wheat and legume portions.
2. Use liquids. Juice, sports drink mix, and maltodextrin based mixes carry hundreds of grams of carbs without the physical volume of solid food.
3. Front load. Put your biggest carb day 2 to 3 days out, not the night before, so race morning you feel light.

My clients’ current favorite load foods, for the record: white rice, pretzels, apple juice, mochi waffles, and dehydrated sweet potato sticks (about 58 grams of carbs a bag, and weirdly addictive apparently).

The influencer corner: no, fat adaptation does not exempt you

If you spend any time on endurance Instagram you have seen the claim: become fat adapted and you will not need all those carbs. The research here is brutal, and the funniest part is that the study keto advocates cite most actually undermines the pitch.

The FASTER study compared keto adapted ultrarunners to high carb ultrarunners and found the keto group burned fat at extraordinary rates. It also found their muscle glycogen stores, and their glycogen use during a 3 hour run, were essentially the same as the high carb group (Volek et al., 2016). Cross sectional, 20 male ultrarunners, no performance test. Glycogen still mattered to bodies that had spent months training it away.

Then Louise Burke’s Supernova trials did what influencers rarely do: measured performance in elite athletes. Elite race walkers on a ketogenic diet massively increased fat burning, and got slower. Their oxygen cost at race pace went up, and while the high carb groups improved their 10 km times by 5 to 7 percent after intensified training, the keto group did not improve at all (Burke et al., 2017). When people questioned the result, her group ran it again and reproduced it (Burke et al., 2020). Applicability caveat: elite race walkers are not weekend gravel racers, and there may be a niche for low carb approaches in very low intensity ultra events (Burke, 2021). But for anything raced at intensity, the fuel that wins is still carbohydrate.

The part the guidelines were not built for: women

Here is a number that should bother you: across 60 years of glycogen loading studies, a 2025 meta analysis counted 319 participants, and only 48 of them were women (Solem et al., 2025).

The classic finding was that women “could not” carb load: in a 1995 trial, men increased muscle glycogen 41 percent while women on the same relative diet increased zero percent (Tarnopolsky et al., 1995). The follow up work found the real explanation: the women were prescribed carbs as a percentage of a smaller energy intake, so they simply were not eating enough. When women increased total energy intake about 30 percent alongside the high carb percentage, they loaded just fine (Tarnopolsky et al., 2001). Dose it per kilogram with adequate calories and the sex difference largely disappears (James et al., 2001).

Practically, for my female athletes this means the load is often a bigger eating project relative to appetite, it cannot be done half heartedly on top of an energy deficit, and race week is the wrong week to be cutting. I have had this exact conversation with athletes tempted to chase race weight into the final days: protecting the load beats saving a few hundred grams of body weight, every time.

The moment that made a client say “wow”

One of my runners recently described her legs going heavy and dead near the end of a long effort, then coming back to life after a couple of energy chews. She asked how that was possible, since the chews could not have digested that fast.

Here is the fun part: fatigue is not just an empty tank, it is also your brain being protective. When carbohydrate availability drops after a few lighter eating days, your brain starts pulling the brake on your muscles before you are anywhere near true empty, and when it senses incoming fuel, it eases off. She had been eating light on carbs for two days before that session. Her legs were not broken. Her glycogen was low and her brain was negotiating.

That is what carb loading actually buys you: not just fuel in the muscle, but a brain that lets you keep pushing.

What I would do this weekend

If your race is under about 90 minutes, skip the formal load, eat normally with 7 to 12 g/kg of carbs the day before, and put your energy into a good breakfast.

If your race is longer, pick a lane. Either 10 to 12 g/kg for the final 36 to 48 hours, or a single rest day load at around 10 g/kg if the shorter window suits your stomach and schedule better. Go lower fiber, lean on liquids, front load the biggest day, expect the scale to jump, and rehearse the entire thing before a key training day so race week is not your first attempt.

And if you want the numbers done for you, this is literally what I do all day. My 1 on 1 coaching includes a personalized race week carb load, gut training plan, and race day fueling strategy built off your actual training data. If you are more of a DIY athlete, grab the free guides and cheat sheets on our free resources page, they are the same frameworks we use with clients.

Fuel like it matters, because it does.

References

Bergström J, Hultman E (1966). Muscle glycogen synthesis after exercise: an enhancing factor localized to the muscle cells in man. Nature 210:309-310.

Bergström J, Hermansen L, Hultman E, Saltin B (1967). Diet, muscle glycogen and physical performance. Acta Physiologica Scandinavica 71:140-150.

Burke LM, Hawley JA, Schabort EJ, St Clair Gibson A, Mujika I, Noakes TD (2000). Carbohydrate loading failed to improve 100-km cycling performance in a placebo-controlled trial. Journal of Applied Physiology 88:1284-1290.

Burke LM, Hawley JA, Wong SHS, Jeukendrup AE (2011). Carbohydrates for training and competition. Journal of Sports Sciences 29(S1):S17-S27.

Burke LM, Ross ML, Garvican-Lewis LA, et al. (2017). Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers. Journal of Physiology 595:2785-2807.

Burke LM, et al. (2020). Crisis of confidence averted: impairment of exercise economy and performance in elite race walkers by ketogenic low carbohydrate, high fat diet is reproducible. PLoS ONE 15:e0234027.

Burke LM (2021). Ketogenic low-CHO, high-fat diet: the future of elite endurance sport? Journal of Physiology 599:819-843.

Bussau VA, Fairchild TJ, Rao A, Steele P, Fournier PA (2002). Carbohydrate loading in human muscle: an improved 1 day protocol. European Journal of Applied Physiology 87:290-295.

Fernández-Elías VE, Ortega JF, Nelson RK, Mora-Rodriguez R (2015). Relationship between muscle water and glycogen recovery after prolonged exercise in the heat in humans. European Journal of Applied Physiology 115:1919-1926.

Gonzalez JT, Fuchs CJ, Betts JA, van Loon LJC (2016). Liver glycogen metabolism during and after prolonged endurance-type exercise. American Journal of Physiology, Endocrinology and Metabolism 311:E543-E553.

Hawley JA, Schabort EJ, Noakes TD, Dennis SC (1997). Carbohydrate-loading and exercise performance: an update. Sports Medicine 24:73-81.

James AP, et al. (2001). Muscle glycogen supercompensation: absence of a gender-related difference. European Journal of Applied Physiology 85:533-538.

Lis DM, Stellingwerff T, Kitic CM, Fell JW, Ahuja KDK (2018). Low FODMAP: a preliminary strategy to reduce gastrointestinal distress in athletes. Medicine and Science in Sports and Exercise 50:116-123.

Olsson KE, Saltin B (1970). Variation in total body water with muscle glycogen changes in man. Acta Physiologica Scandinavica 80:11-18.

Podlogar T, Wallis GA (2022). New horizons in carbohydrate research and application for endurance athletes. Sports Medicine 52(S1):5-23.

Sherman WM, Costill DL, Fink WJ, Miller JM (1981). Effect of exercise-diet manipulation on muscle glycogen and its subsequent utilization during performance. International Journal of Sports Medicine 2:114-118.

Solem K, Clauss M, Jensen J (2025). Glycogen supercompensation in skeletal muscle after cycling or running followed by a high carbohydrate intake the following days: a systematic review and meta-analysis. Frontiers in Physiology 16:1620943.

Tarnopolsky MA, Atkinson SA, Phillips SM, MacDougall JD (1995). Carbohydrate loading and metabolism during exercise in men and women. Journal of Applied Physiology 78:1360-1368.

Tarnopolsky MA, Zawada C, Richmond LB, Carter S, Shearer J, Graham T, Phillips SM (2001). Gender differences in carbohydrate loading are related to energy intake. Journal of Applied Physiology 91:225-230.

Thomas DT, Erdman KA, Burke LM (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: nutrition and athletic performance. Medicine and Science in Sports and Exercise 48:543-568.

Volek JS, et al. (2016). Metabolic characteristics of keto-adapted ultra-endurance runners. Metabolism 65:100-110.