Runners often gather for a pasta dinner the night before a race to eat carbohydrates and socialize. But experts say carbo-loading ahead of a marathon or other endurance event isn’t about one huge, starchy dinner or an endless bread basket.

Despite popular perception, “carbo-loading is not stuffing yourself with pasta,” said Nancy Clark, a sports nutritionist in the Boston area who works with marathon runners.

Carbo-loading is a research-backed strategy of eating and drinking more carbohydrates about two days before a marathon to saturate muscles with glycogen — a form of glucose that’s stored in the muscles and liver that runners use to propel their legs.

Experts say that, in the days ahead of a race, runners should consume extra carbohydrates that are low in fiber and easy to digest — such as bagels, pasta, potatoes and rice — but only until they’re comfortably full.

“You don’t have to necessarily eat more calories,” said Trent Stellingwerff, chief performance officer for the Canadian Sport Institute Pacific in Victoria, British Columbia. “You’re just going to fill more of your plate up with carbohydrates.”

Carbo-loading doesn’t improve performance for athletes running distances such as a 5K or 10-miler, because they are unlikely to burn out of glycogen in the same way a marathoner running 26.2 miles over several hours might.

How to avoid hitting the wall

Humans can only store so much glycogen in their muscles and liver — and it’s not enough to run 26.2 miles. Trained endurance athletes can maintain their pace for around 20 to 22 miles, depending on the runner, said Louise Burke, the chair of sports nutrition at Australian Catholic University. By then, the body’s glycogen runs low and the marathon “starts getting really tough.”

This is what runners refer to as hitting the dreaded wall.

“We just can’t store enough in our muscles and liver to make it through all the way,” said David Nieman, a professor of biology at Appalachian State University who has run 58 marathons. “If you can get more carbohydrate — glycogen — into the muscles and liver, you can maintain your racing pace longer.”

There are three ways runners try to avoid hitting the wall, Nieman said.

First, by training. The more a runner trains, the more glycogen their muscles can store. Second, by tapering. Runners cut back their mileage before a marathon to give their muscles a chance to stockpile the fuel. And third, by eating more carbohydrates before and during a race.

To replenish muscles’ glycogen stores ahead of a marathon, researchers say athletes should ingest around 10 grams of carbohydrates per kilogram of body weight for up to two days beforehand. For someone who weighs 150 pounds, that’s around 680 grams of carbohydrates a day, or about the same as consuming two bagels, two bananas, a 12-ounce glass of orange juice, four cups of white rice, around three dozen gummy bears and two 20-ounce sports drinks.

Instead of sipping water the day before a marathon, opt for a sports drink with carbohydrates, Stellingwerff said. Or, instead of filling half your plate with carbohydrates, aim for closer to three-quarters of the plate — and less protein or fat.

The amount of carbohydrates a runner should eat to fuel a marathon depends on body type, training and how fast a person is planning to run, experts say.

“Athletes who are pushing the boundaries of what they can do,” such as by running for a personal record of some kind, are going to burn more carbohydrates during the marathon, said Patrick Wilson, an associate professor of exercise science at Old Dominion University.

What carbs to eat before (and during) a race

Carbo-loading can leave runners feeling bloated and heavy before a race. That’s partly because, with every gram of glycogen, the body stores three grams of water — and more weight.

“Off the start line, you might feel a bit sluggish,” Stellingwerff said. “But as you proceed through the race, obviously, you’re going to use that glycogen, and you’re also going to use that water for sweating.”

As you carbo-load for a marathon, try to reduce the fiber in your diet; foods high in fiber can add to bloating or, potentially, unexpected bathroom breaks during a race.

High amounts of lactose from milk and fructose from certain types of fruits or juice can also cause bloating or gas, Wilson said. He recommends runners stick to carbohydrates they’re used to, and if they feel bloated from carbo-loading, they can instead focus on fueling during the race.

Marathon runners have to learn how to eat during a marathon, Clark said. During training, start with a small breakfast — say, half an English muffin — before a long run. Then eat animal crackers, gummy bears or sports gels during the run.

“From the day you start training for the marathon, you start training your gut,” Clark said.