I have trained my body, through nutrition and training, to utilize more internal fats for energy as proved by the last two training runs. To recap since the numbers are quite shocking and nothing that you would expect...
The last two longer runs (40.5 miles and 19.5 miles) I have consumed an average of 93 and 27 calories per hour, respectively. That equates into 15 and 7 grams of carbohydrate per hour! Normal sports nutrition recommendations are a minimum of 30 grams per hour. Am I defying science? Don't know but I have to say that my energy level is sustained during the runs and today I pushed the limits by doing some aggressive threshold repeats of 30 minutes, twice, up a 2.6 mile trail that climbs 1200 feet each time.
Part of my question to myself was if I could maintain intensity while feeding a bit less and today I answered that question. Looking back I think a few more calories would have been better toward the end but I lost very little performance the first 3 hours of my run. The last 45 minutes is when my energy became a bit less and pace slowed about 15 seconds per mile. Still, not a bad adjustment.
All in all, my GI distress has been significantly minimized during my runs due to lower calorie intake. My main focus is on my hydration and electrolyte status and I am nailing it most of the time. This has been maintaining my performance from my perspective.
Still some unanswered questions. Will do another metabolic efficiency test on myself this week before the marathon but Saturday is the true test. Race conditions always change things.