Carb Loading Before a Race: A 72-Hour Protocol That Works

Carb loading earned its reputation in the 1970s, when it meant a week of depletion runs, three days of bread and bad moods, and a start line reached bloated. The modern version takes 36-48 hours. It skips the depletion phase, and for events past 90 minutes most evidence puts the gain at a couple of percent. Below is the 72-hour protocol: grams per kilo for each day, the foods that go down without wrecking your gut, and what the scale will do while you eat.

Who should load, and who should skip it

Your body holds a small carbohydrate tank. Roughly 80-100 g of glycogen in the liver and 300-400 g in the muscles, per the ISSN position stand on nutrient timing, and at race intensity it drains. Once it runs low you slow down whatever your heart and lungs have left. In a review of carbohydrate loading studies, Hawley and colleagues found that exhaustion in long events lines up with muscle glycogen falling to about 25 mmol/kg, that starting full postpones that point by around 20% in events longer than 90 minutes, and that where a set distance is covered as fast as possible, high-carbohydrate diets have improved performance by 2 to 3%. Worth knowing: most of those trials ran without carbohydrate during the event. When a placebo-controlled trial gave cyclists a race breakfast and a drink through a 100 km time trial, loading raised muscle glycogen and did not change the finishing time. So treat the load as insurance on the back half rather than a guaranteed number on the clock, and do not let it replace fueling during the race.

For efforts of 60-90 minutes the same review found no benefit. A classic Sherman study showed trained runners with supercompensated glycogen ran a 20.9 km time trial no faster than they did on a normal diet. So:

• Load: marathon, 70.3 and full-distance triathlon, gran fondos, ultras, a half marathon you expect to take over 1:45, a Hyrox past 90 minutes.
• Skip it: 5K, 10K, sprint triathlon, a sub-90-minute half, any strength or CrossFit competition. A normal 5-7 g/kg carb day and a proper breakfast.
• Load and fuel during: anything past 2.5 hours. Loading fills the tank. It does not make the tank big enough for an Ironman, and the Burke review of carbohydrates for competition puts race intake at 30-60 g per hour, and up to 90 g per hour past 2.5 hours. Same numbers you should already be hitting on the long days, covered in fueling around long sessions.

Most people who should load, don't. Among 257 runners at the 2009 London Marathon, those who ate more than 7 g/kg of carbohydrate the day before ran faster and held their speed through the race better, after adjusting for training distance, body size and sex (Atkinson and colleagues). That is an association from a self-reported survey, not a controlled trial, but it points the same way. Of 1,016 endurance athletes quizzed on the loading guideline, 28% got the amount right.

The depletion phase is dead

The original Scandinavian protocol ran three days of near-zero carbs and exhausting exercise before three days of high carbs. It worked. It also wrecked the week that mattered most.

In 1981, Sherman's group compared that protocol with a moderate one (50% carbs for three days, then 70% for three days, all while tapering) and got 207 mmol/kg from the depletion protocol against 203 from the moderate one. Same tank. No depletion.

Then Bussau's 2002 study: eight trained men ate 10 g/kg per day of high-glycemic carbohydrate while resting, and muscle glycogen went from 95 to 180 mmol/kg wet weight in 24 hours and did not climb further over two more days of the same diet. One full day. Eating, no training, and the tank was full. Once full, it stays full: Goforth's group found supercompensated glycogen held for at least 3 days in resting athletes on a moderate 60% carb diet.

So the load is short. Rest is half of it, because every session on a load day burns what you are stacking, and a well-fed rest day two days out does not wear off by the start.

The 72-hour protocol

Guidelines converge on the same band: 10-12 g/kg per day for the 36-48 hours before competition for events over 90 minutes, or 8-10 g/kg for 1-3 days, with training volume cut for 3-4 days. The 72-hour version below uses day three as a bridge, so full loading does not land on a gut that was eating salad on Wednesday.

Read the table like this. Find the row for where you are in the countdown, multiply the target by your bodyweight in kilos, check the example columns for a 60 kg and an 80 kg athlete, and read the training column as part of the protocol, not a suggestion. The evening-meal row sits inside the day-before total. Not on top of it.

Two days at 8-10 g/kg is deliberate. Bussau's data say one can, but the second day covers the athlete who under-ate on day one and tops up the liver. The race-morning meal exists because an overnight fast draws the liver down while muscle glycogen sits tight, and the Mata review puts it at 1-4 g/kg, 1-4 hours before the start: closer to 4 hours and the top of the range for a marathon, closer to 2 hours and 1 g/kg if you cannot eat early.

What to eat so 700 grams goes down

A 70 kg athlete at 10 g/kg needs 700 g of carbohydrate in a day, and that takes a full day of eating with carbs in every slot. Roughly, a 700 g day:

• Breakfast, about 150 g. A large bowl of oats or cornflakes with milk, a sliced banana and a spoon of honey, plus 300 ml of orange juice.
• Mid-morning, about 100 g. A bagel with jam and 500 ml of sports drink.
• Lunch, about 150 g. A big plate of white rice with a small portion of chicken or fish, plus fruit juice.
• Afternoon, about 100 g. Rice cakes with honey, a banana and a second bottle of sports drink.
• Dinner, about 150 g. Pasta with a tomato-based sauce, white bread on the side, a small piece of lean meat.
• Evening, about 50 g. Low-fat yogurt with honey, or a glass of juice.

The principles behind the menu:

• Low fiber. From 48 hours out: white rice over brown, white bread over seeded, peeled potatoes, juice over whole fruit. In Rehrer's survey of 55 male half-Ironman triathletes, every athlete who had intestinal cramps had eaten fiber-rich food in the pre-race meal. Of those without cramps, 10% had.
• Low fat, moderate protein. Fat slows digestion and fills you up before you reach the grams, and in the same survey, fat and protein intake was higher in the athletes who vomited. A palm of lean protein at meals, and no cheese, cream, pizza or fried food.
• Liquids for volume. Juice, sports drink and smoothies put down 30-60 g a glass without the chewing.
• Some fructose. Fruit, juice, honey and table sugar bring fructose, which goes mainly to the liver, and Gonzalez and colleagues report that pairing glucose with fructose or galactose doubles post-exercise liver glycogen repletion. Whether the same holds on a rest day has not been tested, but the fructose is worth having either way.
• Salt. You are about to store a liter or so of water. Salt the rice.

The scale goes up, and that is the point

Every gram of glycogen is stored with water. A 2015 biopsy study measured at least 3 g of water per gram of glycogen during refueling, older body-water research puts it at 3-4 g, and a 2023 review of glycogen and hydration puts the typical bodyweight gain during a load at 1.0-1.5 kg, mostly water, while noting that how much of that water is bound to glycogen is still unsettled.

That is the load working. Your legs may feel heavy and full on the shakeout jog. Normal. Do not respond by cutting the rice on the last day, and weigh in on the morning of day three and on race morning to learn your own delta. Some of that water is thought to come back out as the glycogen burns, though how much is not settled. If race day will be warm, pair the load with your own numbers from a sweat rate calculator and the hydration tracking guide.

Women, big athletes, and the low-carb crowd

Women need to eat more, not swap. Tarnopolsky's lab fed trained women 75% carbohydrate at their usual energy intake and got no rise in muscle glycogen, then the same 75% with total energy up about a third, and their glycogen went up. The old "women cannot load" finding was an energy problem. A female athlete on 2,000 kcal a day does not reach 8 g/kg by moving calories around. The load goes on top. The ISSN stand says the same, and the wider picture of how the numbers differ by sex is in female vs male fueling. If adding food on race week feels like a lot, that is often a sign the everyday intake is short, which is the territory of low energy availability.

Over 85 kg, use the low end. At 12 g/kg a 90 kg athlete is looking at 1,080 g in a day, so take 8 g/kg across both loading days and lean on liquids.

Low-carb and keto athletes: a gut that has not seen 600 g of carbohydrate in months will not accept it quietly on race week. Rehearse in training, or race the way you train.

On a GLP-1, spread it out and lower the target. Gastric emptying is slower, so the grams that were comfortable before are not now. Use the low end of the range, take more and smaller feeds, and put breakfast closer to 4 hours out than 2. If the prescription is for blood sugar rather than weight, talk to whoever wrote it before you eat 700 g of high-glycemic carbohydrate in a day. The GLP-1 and training guide covers the rest.

Mistakes that waste the load

• Loading for a week. Glycogen plateaus after a day or two; the rest becomes fat and a gut that is tired of rice. Two days, three at most.
• Training through it. Bussau's athletes were inactive, the ISSN stand says cut volume sharply, and a 60-minute run on day two burns a chunk of what you ate at lunch.
• The pasta-party binge. One 250 g plate of pasta at 21:00 the night before gets you a bad night's sleep, a heavy stomach at 07:00 and maybe 90 g of carbohydrate.
• Anything new. A new gel, a new restaurant. Race week is the wrong time to find out.
• Skipping breakfast, or eating on the start line. The liver empties overnight and breakfast refills it, but in Rehrer's triathletes everyone who ate within 30 minutes of the start vomited during the swim. Eat 3-4 hours out. Then sip.
• Forgetting the fluid side. Concentrated, hypertonic drinks went with severe symptoms in that same survey. Sports drink at label concentration, water alongside, sodium with the food.
• Doing it for the first time on race week. Run the full protocol once before your longest training session, 3-4 weeks out: two loading days, the early dinner, the race breakfast, and the in-session fueling from a race nutrition planner, then weigh in before and after and write down what your gut did at hour two. That rehearsal doubles as the last big session of your gut training, and how to fuel a marathon picks up where this guide stops.

How Movement Rebels fits

A load only works on a rested body. Race week is where most plans quietly fall apart: one more sharpener on Thursday, a heavy leg day someone forgot to move. Set the volume drop with the taper calculator, and how to taper has the reasoning behind the numbers. The Movement Rebels coach reads your Garmin or Apple Health activities and your logged lifts, and when you tell it the race date in chat it can rebuild race week so the last heavy lower-body session sits a week out and the final 72 hours hold a short sharpener, then a shakeout, then rest. With auto push on, those sessions land on your Garmin, and your morning check-in plus the HRV, resting heart rate and sleep coming off the watch tell you whether the taper is landing.

Rebel Fuel is your own log for the gram counting. Set the daily target with the carb loading calculator and log the feeds so the menu is there to repeat. The coach does not read meal logs, so put "carb loading Thursday to Saturday, racing Sunday" in Notes for your coach and the brief reads it next to your watch data. After the race, the post-activity analysis from your Garmin or Apple Health sync shows the per-kilometer splits. That is where you find out whether the last 10 km held.