Every October I hear the same plan. A big pasta dinner Saturday night, maybe a second helping, and the fuel is handled. It is a comforting ritual. It is also built on a misunderstanding of how muscle stores carbohydrate.
Chicago is six days away. New York is four weeks. If you are racing either one, the next few days of eating matter more than most of the training you have left. They also matter in a different way than the pasta dinner suggests.
The myth: the night before is when you load
The belief is simple. Eat a huge meal the evening before and you wake up with a full tank. The trouble is that muscle does not fill like a gas tank. It fills slowly, over many hours, and it fills best when the muscle is rested and carbohydrate keeps arriving.
One dinner cannot do that. A large meal the night before also tends to arrive on top of nerves, a disrupted routine, and a stomach that would rather be empty. The runners who feel flat and heavy at the start line are often the ones who tried to do the whole job in one sitting.
What glycogen is, and why a marathon drains it
Glycogen is the stored form of carbohydrate. Your muscles keep it right where the work happens, and your liver keeps a separate supply that helps hold blood sugar steady. At marathon pace, your legs lean heavily on that stored carbohydrate. Fat supplies a lot of the energy too, but it cannot be burned fast enough to hold marathon pace on its own.
Run long enough and the stores run low. That is the wall. It is not a mystery and it is not a character flaw. It is a fuel supply problem, and the part of it you can influence before the gun goes off is how full the tank is at the start.
The reason loading works at all was shown back in 1967. Bergstrom and Hultman demonstrated that muscle glycogen could be raised above its normal level with the right combination of exercise and diet. That finding is called supercompensation. The muscle, given rest and plenty of carbohydrate after depletion, stores more than it did before.
Two days, not one, and not three
The early protocols were brutal. They asked athletes to run themselves empty a week out, eat almost no carbohydrate for three days, and then flip to high carbohydrate. It worked, and it left people miserable. Nobody needs to do that to themselves a week before a goal race.
The modern version is far simpler. Gareth Wallis and Tim Podlogar, writing in the Gatorade Sports Science Institute's Sports Science Exchange, give the target as 10 to 12 grams of carbohydrate per kilogram of body weight per day for 36 to 48 hours before competition. They also note that the amount can be scaled, from about 7 to 12 grams per kilogram, depending on the demands of the event.
A study by Bussau and colleagues in the European Journal of Applied Physiology in 2002 gave a useful clue about how fast this can happen. Eight endurance-trained men ate 10 grams per kilogram of high-carbohydrate foods and stayed inactive. Muscle biopsies showed that glycogen had increased significantly after just one day, with no depletion phase needed first.
That does not mean one day is the plan. It was a small study under controlled conditions. What it tells you is that the muscle responds quickly, and that two days gives you a buffer if one meal goes wrong.
What 10 to 12 grams per kilogram looks like
Do the math before you shop. A 70 kilogram runner, about 154 pounds, is looking at 700 to 840 grams of carbohydrate a day. That is a lot of food, and most of us do not eat that way. It is also why the attempt fails when it is left to one dinner.
For Chicago this Sunday, that means Friday and Saturday. For New York, it means Thursday and Friday of the week before, with a lighter, familiar Saturday. The principle is the same either way. Spread the carbohydrate across the whole day instead of stacking it on the last meal.
A few things make the volume manageable:
- Shift the plate. More rice, bread, potatoes, oats, and pasta. Less of everything else.
- Lean on low-fiber, low-fat choices. White rice and plain bagels sit easier than a salad and a cream sauce.
- Drink some of it. Juice, sports drink, and smoothies deliver carbohydrate without the bulk.
- Eat small and often. Five or six smaller meals feel better than three huge ones.
Nothing here should be new. Save the unfamiliar foods for after the race.
Why the scale goes up
Water is stored alongside glycogen as it is built. Wallis and Podlogar point to this directly: the body holds water as part of the storage process, which is why loading can add body weight before the race. It is also why they recommend scaling the intake to the event instead of loading at the maximum every time.
So expect to weigh a bit more on Saturday, and expect your legs to feel a little full. It is not fat gain and it is not a sign that you did it wrong. That water comes back off during the race as you burn through the glycogen.
If the scale makes you anxious, decide now that you are not going to look at it this week. The number does not tell you anything useful on race weekend.
Rest is half the protocol
Loading works best when you are not running much. That is the other reason the taper and the loading window are paired. Glycogen is built in rested muscle. If you are still running long and hard on Friday, you spend carbohydrate while you are trying to store it.
This is the part people miss when they copy the eating without the resting. The two together are the protocol. Short, easy runs, plenty of sleep, and carbohydrate at every meal.
What the evidence does and does not say
Here is where I want to be careful, because carb loading gets oversold.
The evidence that this approach raises muscle glycogen is strong and old. The evidence that it makes a runner faster over a given distance is weaker, and it depends on how long the race is. The Wallis and Podlogar review cites a 1981 study by Sherman and colleagues in which the higher-carbohydrate approach raised glycogen but did not improve performance over a half-marathon-length run. A full tank only helps if you would otherwise run out.
That is the logic for the marathon. A race that takes well over two hours is the case where glycogen is most likely to become the limit. For a 5K or a 10K, aggressive loading is mostly unnecessary. I would call it reasonable insurance for the marathon, not a guaranteed time drop.
Loading also does not replace what you eat on the course. Burke, Hawley, Wong, and Jeukendrup reviewed carbohydrate timing in the Journal of Sports Sciences in 2011. For long events they describe 30 to 60 grams per hour as an appropriate target, with intakes up to 90 grams per hour for events beyond 2.5 hours. A full start and steady fueling are two halves of one plan.
My wife Aubrie has run a 2:59 marathon and finished more than ten of them. The part I would pass on from that experience is the boring part: rehearse it. The start line is not the place to find out how your stomach handles a high-carbohydrate day.
Where NXT RUN comes in
The hardest part of race-week fueling is not the science. It is that you have probably never practiced it.
PACE Create can help with the rehearsal. Tell your coach you want a long run built to practice fueling, and it builds the session: the distance, the paces, and the structure. Run it a few weeks before race day, use the foods and timing you plan to use, and you will know what works before it counts.
This article is general education, not medical or dietary advice. Carbohydrate targets in the research are based mostly on healthy, well-trained adults. If you have diabetes, a digestive condition, or any other medical issue that affects how you eat, talk with your doctor or a registered dietitian before changing your diet for race week.