I just found this marathon nutrition tips by Marathoner Deena Kastor.
It’s a good idea to know which foods provide the biggest carbohydrate bang per serving, but you don’t necessarily have to approach each meal with a fork and a calculator. Marathoner Deena Kastor, who won bronze at the 2004 Olympics, believes that once you understand how your body processes different carbohydrates — that is, which foods provide lasting energy for you — you can approach your meals with an intuitive sense of what you need.
“I focus on adding another heaping spoonful of pasta or a few more potatoes,” she says. “Before the Athens marathon, I also ate a lot of dense fruits with high sugar content: pears, bananas, grapes. They replaced a lot of electrolytes and minerals I knew I was sweating out.”
Read original article calculating carbs for endurance athletes