If runners at this weekend’s California International Marathon want a dose of energy-boosting carbs during the race, they won’t find it in the paper cups at aid stations.  

Instead, volunteers will hand over Nuun, a sugar-free sports drink containing electrolytes, vitamins, and only a trace of carbs. For midrace carbs, How I Broke a 3:30 Marathon After a Long Break Nutrition - Weight Loss.

Sunday’s race marks the second time CIM has partnered with Nuun as its official nutrition sponsor. The event held in Sacramento is not alone in offering sugar-free fluids. 

This year, Nuun, serving varieties from its “Active” line, was the official on-course beverage at more than 150 events, including the Nike Women’s Half Marathon in San Francisco and the BolderBoulder 10K in Boulder, Colorado. 

Ultima Replenisher, another low-carb sports drink that contains no sugar or artificial ingredients, was the on-course beverage at 2015 events like the Portland Marathon in Oregon and the Runner’s World Half Marathon & Festival Races - Places.

“When we made the decision to do this, we took into account the fact that we have 6,000 marathoners who have 6,000 different sets of nutritional needs,” CIM race director Eli Asch told Runner’s World. “What Nuun offers runners is the ability to customize their own plan that fits them the best, because they can separate their caloric intake needs from their electrolyte and fluid intake needs.”

Founded in 2004, Nuun is known for its dissolving tabs that add flavor and electrolytes but not carbs to water. A 12-ounce serving of Gatorade, by contrast, serves up 21 grams of carbs, in the form of sugar and dextrose. 

The emerging trend of low or no-carb drinks in races has garnered mixed reactions from runners—especially those tackling longer events like half and full marathons. Some runners on the website LetsRun.com sounded off Running in the Cold Antonucci said she hopes the trend will pass. 

“For the cost of entering a marathon, especially one like CIM that fancies itself as a borderline U.S. major, you would think that a race director would honor runner needs before sponsorships that benefit the bottom line,” said one poster. 

Not all runners are opposed. Sheila Shoemaker, who ran CIM last year, said she was happy to find out the event was providing Nuun. During training, she supplemented Nuun with Clif Shot Bloks. 

“It seems like Nuun gives me more of an output that lasts instead of a sugar rush and a crash,” said the 28-year-old from Sacramento. “And it has a lighter taste.” 

Asch said the reaction from participants has been largely positive, adding the event provides two nutrition and fueling seminars at the expo to alert participants in advance of race day.

Next year, Nuun plans to offer its new “Plus” line, which contains 11 grams of carbs per serving, at the races it sponsors. 

Lauren Antonucci, R.D.N., C.S.S.D., of Nutrition Energy in New York City, nutrition consultant for the New York Road Runners, and 13-time marathoner, said offering low-carb fluids is “completely counterintuitive to everything we’ve been taught as runners and athletes.”

“In practicality, [low-carb drinks] is probably making it harder for people,” Antonucci said. “When you’re out there, it’s easier to get enough carbs and calories and sodium in a drink than from a million little chews. Those are useful, but it’s hard to take in 300 calories in chews in an hour.”

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“As a marathoner, I am not happy to see those out on the course,” Antonucci said. “The science doesn’t support either lower carb products as fueling or hydrating athletes better or that splitting up the carbs and electrolytes is better. The science is still there saying that we need the carbs.” 

As always, a key part of race preparation involves researching ahead of time on-course fuel offerings. You can then practice consuming those products during training or CA Notice at Collection during the race.