As athletes around the world gear up for the annual New York City Marathon Sunday, many will be focused on their last-minute preparations, including a final pre-run meal.

And as the famous mantra goes, it’s time to load up on carbs, right?  Not necessarily, according to new research from Dr. Jeff Volek, a professor in the department of human sciences at The Ohio State University, and Colette Heimowitz, a nutritionist and vice president of nutrition at Atkins Nutritionals, Inc.

In 1925, researchers found that blood glucose decreased during the Boston Marathon and that injecting glucose into an athlete improved their performance.

“The recommendation of a high-carb diet came based on that theory, and then in 1967 the nail was put into the casket because through muscle biopsies they found the importance of glycogen,” Heimowitz told FoxNews.com. Glycogen is where carbohydrates are stored in muscles.

However, Volek tells FoxNews.com it’s time to question that theory.

“We have this legion of ultra-endurance athletes who are abandoning their high-carb diets and instead following a low-carb moderate protein diet,” he said.

It takes the body an average of three months to fully adapt to a low-carb diet, but the benefits are numerous, including enhanced performance and longer endurance, according to Volek.

“The most remarkable finding is that these athletes have extraordinarily high rates of fat oxidation, or fat burning, so they burn fat at twice the rate as their high-carb counterparts do,” he said. “This is really important because during a marathon or a race lasting longer than a few hours, you burn through your carbohydrates.”

According to Heimowitz, these long races are where an athlete may “hit a wall.”

“We have a limited capacity to store carbs, but an unlimited capacity to store fat,” she said. Adapting to a low-carb diet would mean a runner wouldn’t have to worry about stocking up on much ahead of the big race.

Additionally, a fat-adapted athlete wouldn’t have to rely on food as much during exercise, compared to carb-eaters who have to monitor calorie intake and consume gels during a race.

“[Fat-adapted athletes] can generally compete for several hours without having to consume any calories. That’s a major advantage because it’s not something that athletes want to do, stop during their exercise to ingest food – which is also easier on the GI [gastrointestinal] tract,” Volek said.

But both Volek and Heimowitz agree that high-carb athletes should not attempt a low-carb diet in the days leading up the race. As the body adapts to a fat-for-fuel technique, performance may decrease over the first few weeks.

“Don’t go out and try to set up some training record in the first week,” Volek said. There’s also more to the diet than cutting pasta and bread foods. “You have to get the protein right, understand which sources of fat are preferred for the body, and there’s also a change in mineral balance,” Volek said, adding  there’s a certain level of knowledge required before embarking on this diet.

For athletes entering Sunday’s marathon, it’s not too late to take last-minute steps to ensure you perform at your best.

“If you’re on a high-carb diet, you can have some pasta, but it shouldn’t be five pounds because you’re only going to have diarrhea the next day and you’re going to run through it quickly,” Heimowitz said.

“It’s better to eat the slow carbs, it’s gentle on the stomach, it’s slow to digest and it minimizes insulin production,” she said. “The slow-release carbohydrates extend the blood sugar to remain steady.”

Heimowitz said the ideal night-before meal would be to eat low-fiber foods to avoid rapidly cleaning your stomach: a protein like fish or chicken, salad with an olive oil dressing, and half a sweet potato.

When the race ends, researchers found that those on the low-carb diet may have an easier time recovering than their high-carb counterparts, but Volek also noted other health benefits from the diet that will last long after you cross the finish line.

"Managing the risk for diabetes, reversing type II diabetes, improving your cholesterol level and lowering the risk of heart disease," are things, according to Volek, that can be a result of a low-carb diet, "when you get it right."