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Can swishing carbs improve your race time?

Repeated mouth rinse studies have running world questioning the results


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Late in the 2015 London Marathon, two elite Kenyan runners were running stride for stride, battling for the lead going into the final mile.

Wilson Kipsang, who had won the race the year before, was one of two favorites to win the race. But the other, Eliud Kipchoge, had surprised the field by grabbing a share of the lead. As they reached the 25-mile mark of the race, Kipsang ran right past the final drink station. After all, he was less than seven minutes from the end of the race. He’d reach the finish line well before any of the sweet sugary fuel would reach his muscles.

Kipchoge, on other hand, grabbed his bottle, and minutes later surged in the final half mile of the race to beat Kipsang by five seconds.

Did the late drink have anything to do with the thrilling finish? Perhaps.

A growing body of research over the past two decades has suggested that merely taking carbohydrates by mouth can improve athletic performance even before those calories can be absorbed. While the findings remain controversial in competitive circles, a number of endurance athletes are adding a late drink to their hydration strategies for longer races or drinking carbohydrate beverages in shorter events where their energy supply is never in question.

Researchers believe that receptors in the mouth may signal to the brain that carbohydrates are on their way, allowing the body to push through fatigue or to work harder without feeling any additional exertion.

Filling the tank

The body mainly relies on fat and carbohydrates for energy during exercise. While athletes can store a lot of energy as fat, burning fat as fuel is a slow process that can’t keep up with the demand of high-intensity exercise like running or cycling.

Carbs are more readily available in the form of glycogen in the liver or muscles but are limited in supply. Glycogen usually runs out after 90 to 180 minutes of intense exercise, forcing the body to switch to burning fat instead. That’s what runners call bonking or hitting the wall.

For longer pursuits, replacing the glycogen by drinking a sugary sports drink can help push back the wall. For races of less than 90 minutes, it was always considered pointless to refuel mid-race.

But a lab experiment conducted in 1997 called that notion into question. Researchers led by Asker Jeukendrup at the University of Birmingham in the U.K. had found that cyclists in a 40-kilometer time trial finished about a minute faster when they consumed carbs during the hour-long race. It was a large and unexpected effect that they couldn’t explain.

“During exercise of one hour or less duration, you don’t run out of carbohydrate and your blood sugar concentration does not drop,” Jeukendrup wrote on his blog last year. “So why would ingesting carbohydrate during exercise have any effect?”

The researchers tried another experiment, where they infused glucose intravenously during a simulated bike race, making huge amounts of glucose available for the muscles to burn right away. But in those tests, the cyclist did no better than controls who received saltwater. For some reason, the cyclist had to take the carbs by mouth to see an effect.

That got the researchers thinking. They duplicated their experiment but asked the cyclists to rinse their mouth with a carbohydrate solution and to spit it out.

“The results were remarkable,” Juekendrup wrote. “The magnitude of the effect was the same as the effect we had seen in the earlier study with carbohydrate ingestion. They were about 1 minute faster even though none of the carbohydrate had actually entered the body.”

The researchers concluded the mouth must contain receptors that sense the carbohydrate and signal the brain. The taste of carbohydrates seems to block fatigue in the brain and improve performance when exercise lasts about an hour.

Jeukendrup recently highlighted the results of 15 follow-up studies that tested the effect in varied conditions in events lasting between 35 and 75 minutes of duration. All but three showed a performance benefit between 2 to 12 percent. No studies have shown an effect in events lasting less than 30 minutes.

The findings were not altogether unprecedented. Studies have shown that taste affects mood, so could it impact perception of effort? And athletes who have depleted their glycogen stores with a long run or ride say they need only bite into an energy bar to feel better.

Race day hydration

But the finding has been controversial. Many nutritional studies ask test subjects not to eat anything the morning of the study, to keep the contents of their breakfast from skewing the test results. But no competitive athlete would race in a fasted state, and tests with mouth rinsing among fed athletes didn’t show the same results. And in longer events, intake of carbohydrates earlier in the race may trump its impact.

Max King, an ultramarathoner from Bend, said he sees limited benefit to the strategy.

“It works to some extent at fooling your body,” he said. “The case where I can see this actually working is in a shorter distance race where you just need a little more carbs to get to the finish feeling good and taking any carbs in will upset your stomach causing more harm than good.”

Like Kipchoge, several marathoners have adopted a late-drink strategy. Famed marathoner Meb Keflezighi routinely grabs his bottle at the 25-mile mark of the marathon to rinse and spit. And some professional cycling teams are now placing drinks in their bicycles’ bottle cages in time trials lasting less than an hour.

Some studies have found that rinsing the mouth with carbohydrates was more effective than actually swallowing the carbs. But researchers believe that’s probably because test subjects were asked to swish the carb around in their mouths for five to 10 seconds before spitting, and so the carbs stayed in the mouth longer than when the athletes just drank normally.

The strategy might also have some value for those athletes who intentionally train in a fasted state, trying to force their body to become more efficient at burning fat.

Beyond those narrow uses, however, the mouth rinsing technique — whether you spit or swallow — may not offer much.

“Most studies have found that it’s not beneficial in other modes and longer duration events,” said Stephanie Howe, an ultramarathoner and a sports and nutrition coach in Bend. “It only seems to be helpful at high intensities, so the weekend warrior may not actually benefit from carbohydrate rinsing as elite cyclists do in short, high-intensity time trials.”

Howe advises clients to focus more on good prerace fueling before shorter races like a 5K or 10K and to refuel with a sports drink for half marathons or longer races.

She added, “If you have been fueling for hours, there is no benefit.”

A growing body of research over the past two decades has suggested that merely taking
carbohydrates by mouth can improve athletic performance even before those calories can be
absorbed. While the findings remain controversial in competitive circles, a number of endurance athletes are adding a late drink to their hydration strategies for longer races of drinking carbohydrate beverages in shorter events where their
energy supply is never in question.