Carb Loading For Marathons
By GRETCHEN REYNOLDS New York Times
What you eat, and when you eat it, in the days before a marathon may influence your race time.
It appears that despite the depredations of the big storm, the New York City Marathon is likely to take place as scheduled on Sunday. While the 47,000 runners entered have too little time to remedy any major lapses in training, there is one element that can still be tweaked, two new studies show: what to eat in the days before the race.
The ideal composition of a pre-marathon diet has been somewhat in dispute recently. For years, marathoners were told that they should swallow as many carbohydrates as possible in the week leading up to the race in order to “load” their muscles with stored carbohydrates, or glycogen, the readiest energy source for working muscles.
But such prolonged carbo-loading often leaves runners bloated and heavy; when muscles pack in glycogen, they also add water, and therefore weight, which must be hefted throughout the 26.2 miles of the marathon. Women, in particular, have been found in some studies to benefit little, if at all, from prolonged carbo-loading before marathons.
However, a study published last month in The International Journal of Sport Nutrition and Exercise Metabolism found that carbo-loading can be effective for both men and women — but is best if it’s truncated, encompassing only a day or so of dietary manipulation.
For the study, researchers at the University of Minnesota turned to a ready-made pool of volunteers, consisting of students enrolled in Physical Education 1262: Marathon Training, who were aiming to finish the local Eau Claire Marathon for class credit.
Forty-six students joined the study, 36 of them women and all but two of them first-time marathon runners.
Several weeks before the event, the runners completed a two-mile time trial, to determine their endurance and running ability.
Then, beginning three days before the race and continuing through breakfast on race morning, they kept detailed food diaries. They also noted, to the extent possible, what they ate and drank during the race.
All of the students finished the race, with an average time of 4 hours 43 minutes (and, one would hope, an A grade in P.E.).
But, statistical analysis showed, those runners, both men and women, who’d eaten the most carbohydrates on the day before the race finished faster than those who’d eaten fewer carbohydrates that day.
These results neatly replicate those of a larger study published last year of 257 male and female runners who completed the 2009 London Marathon. Those runners also kept detailed food and training diaries, which researchers compared with their finishing times. In this case, the scientists also tracked each runner’s pace at five-kilometer increments throughout the race.
They found that, as in the Minnesota study, runners who’d loaded up on carbohydrates the day before the race ran faster than those who had eaten fewer carbohydrates. The difference was especially striking beginning at about the 18-mile mark, just when many runners famously “hit the wall” and feel their energy flag. The carbo-loaded runners jauntily maintained their pace. The others did not.
In both studies, carbohydrates eaten at breakfast on race day, during the race itself or on days earlier in the week were relatively unimportant. It was primarily what people ate on the day before the race that mattered.
And yet, few of the runners in either study actually consumed enough carbohydrates to benefit, even if they thought that they were doing so. In both studies, the minimum effective “dose” of carbohydrates was at least six or seven grams for every kilogram of a person’s body weight, or about a quarter-ounce of carbohydrates for every 2.2 pounds of body weight. By that formula, a 220-pound runner would need to consume at least 25 ounces, or more than 700 grams, of carbohydrates on the day before a marathon to finish faster.
In the Minnesota study, fewer than a quarter of the marathoners consumed that many of carbohydrates on the day before the race. In the London study, barely 12 percent did.
What those numbers suggest is that many more marathon runners could benefit from a brief bout of carbo-loading than currently do. And the process itself is relatively simple, says Patrick Wilson, a graduate student at the University of Minnesota who led the study of novice runners. You don’t need to increase your food volume or calories the day before a race; just replace some fats or proteins with carbohydrates.
“I often tell people to choose relatively concentrated sources of carbs, like juices, pasta, rice and sweets,” Mr. Wilson says. “That way, the volume of food needed isn’t so enormous.” In addition, he says, “lower-fiber foods may be good, since that could reduce the potential for stomach distress during the race.” (According to a rather intrusive study this year, extremely high intake of carbohydrates was associated with faster times during endurance races but also with “nausea and flatulence.”)
Don’t completely upend your normal diet, though. “Stick to foods that are familiar,” Mr. Wilson says. “It’s always a bad idea to experiment right before a race.”
And don’t expect that diet alone will lift you from the back of the pack. In the British study, every increase of 1 gram per kilogram of body weight in the carbohydrates that runners consumed on the day before the race increased their speed by about 0.1 miles per hour.
Far more important in the overall determination of people’s finishing times was their training and their fundamental fitness. In the Minnesota study, the runners who were fastest during the time trial were fastest in the marathon, too.
You can’t alter your training or talent at this point. You can, though, have a chocolate chip cookie on Saturday and call it race preparedness.