Experience From - Karl King, Rich Schick, George Beinhorn , Karl King #2,
"I read George B's post on how to run your first 50 miler and he advises water only for the first hour followed by sport drink. I've tried it in my long runs and the hit of hammer gel and sport drink after the first hour seems like rocket fuel. My buddy (a muscle head so take it with a grain of salt) claims I'm just depriving the body of fuel for the first hour so of course I feel more energy after the switch."
If the carbohydrate bump gives you a big boost, it is a sign that your level of blood glucose was on the low side. That wouldn't have happened if you'd been taking carbos from the start.
An important factor is how hard you run the early miles. If you go out too fast, you'll burn a lot leg muscle glycogen and have to run the rest of the race in a depleted state.
If you start slowly, you'll burn less glycogen and switch over to fat burning sooner. There is some justification for doing training runs with water only at the start, but doing races with carbos from the start. Starting with water only, and a fully aerobic pace, should train your body to slip easily into a fat burning mode.
Since not many people run ultras compared to shorter distance events, the question of optimum caloric input early in an endurance event is not a highly studied subject. One can make reasonable arguments either way, and there could be enough variation person to person to obviate a one-size-fits-all solution. For example, the guy who won Grandma's Marathon recently drank no water during the run. That's no calories and no water early, but not something I'd suggest runners do.
Calories early, or water early, is something that each runner can try and see what works for them. One thing to look for is not only performance during the run, but recovery afterward. My personal experience is that anytime I restrict energy input, my recovery is poorer.
Empirically, I see top runners pounding calories from start finish. There's no doubt that when speed is important, carbos are needed for fuel. Fat is the supreme energy storage fuel for endurance, but carbos are the supreme fuel for speed. Protein isn't a good fuel for either.
from a theoretical standpoint I have always felt that it is best to avoid taking on calories within 30 minutes of the start of run until you are 30 minutes into the run. This has to do with the way the pancreas works. It secretes insulin in response to the need for sugar to get out of the blood stream and into tissues to prevent your blood sugar from getting too high. Al Howie is very familiar with this process as his is defective and as a result he suffers from diabetes.
If you are not exercising there is immediate secretion of insulin as soon as the body senses a rise in blood sugar in response to eating or drinking anything that has much in the way of calories. After about 30 minutes of continuous exercise the body gets the message that the sugar needs to stay available in the blood stream for use as a fuel. Its one starts to consume calories prior to that the body sends enough insulin to lower the blood sugar to normal levels as if you were not exercising. If you are exercising and burning calories and an increased rate you can over shoot the mark and drop your blood sugar be low its normal minimums. This can make you feel quite weak and then some individuals even result in a hypoglycemia (very low blood sugar) which may result in the person becoming disoriented and in extreme cases even losing consciousness.
I have to agree with Karl. All dietary advice should be considered first as specific to the person recommending it, and then tested to see if it also works for you.
The reason I like to wait an hour before taking any drinks, etc. during a race is that my body seems to like it i.e., during the first hour it's busy adapting to the demands of running. Anything I put in my tummy during that time feels kind of yucky, like the body is telling me: "Hey! Whaddaya think you're doing?"
My nickname is Mr. Oldandslow, so I'm definitely not shooting out of the starting blocks like a rocket. "Start slow and taper off" about says it.
My experience fits with what Rich described. If I take in a high glycemic index carbo source 30 minutes before running, the run gets ugly after the first mile or two. My blood sugar drops and I have to shuffle along until the body adjusts to the low blood sugar. Two to three miles later, I can start running again.
What works for me is to have a low glycemic index breakfast (complex carbos with some fat and protein ) well before running. Between the meal and the run I'll sip on some water. Usually I don't start drinking much sport drink until the first mile or two is passed. By that time, the body has adjusted to the exercise and low blood sugar is not a problem.