Question: how many calories should you eat during a marathon?
Answer: The ideal is 100 to 250 calories (or 25 to 60 grams of carbs) per hour, after the first hour of running, says Nancy Clark, M.S., R.D., author of Nancy Clark's Food Guide for Marathoners. That's the equivalent of one to 2 1/2 sports gels or 16 to 40 ounces of sports drink per hour.