Marathon fueling

"Determining your total calorie needs

Step 1: Determine running calorie expenditure per mile
0.63 x body weight (pounds)

Step 2: Determine goal race pace or how many miles per hour you'll cover
Example: An eight-minute miler will cover 7.5 miles/hour

Step 3: Calculate hourly expenditure based on goal race pace
Example: An eight-minute miler would multiply 7.5 by the figure from step 1.

Step 4: Determine hourly calorie replacement needs
0.3 x the figure from step 3 (Note: Research shows runners can physically absorb about 30 percent of what they expend.)"

Link

Interesting. . .

See Kim Mueller's full article for some applied case studies.