Horne said her stomach problems seemed connected to the high-carbohydrate gels and health bars marketed to runners.
"I tried those, and they did not work for me; they really destroyed my stomach," said Horne.
A trip to the nutritionist to help her find other foods, and careful training to ease her knee pain has made Horne much more hopeful this year.
But some elite marathoners have ignored this problem and kept running through stomach problems to win a race.
Elite long-distance runner Uta Pippig came from behind to win the 1996 Boston Marathon, despite showing visible signs of menstrual problems and diarrhea while she ran, according to reporting by the Boston Globe.
But, for all the unpleasant side effects, marathoners say they are happy to live through the accomplishment and feel the better for it.
"The benefit of running has all the health benefits -- decrease in blood pressure, stronger heart, decreased risk of diabetes," said Maharam, who will be in charge of all medical teams attending this year's ING New York City Marathon.
Despite the images of extreme pain, sweating, and breathing, Maharam says running a marathon is relatively safe if the runner has prepared properly.
But, Maharam said, one thing marathoners should do to make race day even safer is to be wary of drinking a lot of water. Consuming too much water on race day could lead to something called hyponatremia, or water intoxication.
"If you walk or run a race more than 10 miles, it could be an issue," said Maharam.
According to Maharam, when runners exercise in long distances, a lot of blood flows to the muscles and away from the internal organs like the stomach or kidneys.
"That's why if you try to feed a runner when they finish, they throw up," said Maharam.
The effect on the kidney is to reverse its normal functioning. Instead of ridding itself of excess water, the kidney keeps it.
"You pee out salt to retain free water. Even if you drink Gatorade, you pee out salt to retain free water," said Maharam.
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