Rasmus won my little contest and the prize was that I'd write on whatever subject he chose. He wants to know what to eat during an ultra; that's a tall order, especially for me. I have never eaten a gel or swallowed an electrolyte caplet during a race, so I go against conventional wisdom.
First, there's the matter of how long a race one's dealing with. One can run a 50K on just water (even no water!); I've done it. I even did 50 miles without a water bottle, though it was a mistake. It's when one get to 100 miles that food gets to be an issue and so that's where I'll focus.
"What do people usually do? What do the top runners do? Is there any science behind it?" are his big questions. Well, some live on gels and pills, some are vegans, some eat only dried meat and some eat whatever sounds good at the time.
Chris Gardner won the Superior 100, reportedly consuming three gels per hour for the 21 hours, with nothing else but fluids. I have the data for the popular Hammer Gel in front of me, so that's about 5700 calories (nearly all as maltodextrin) and 1600 mg. of sodium. That's a normal day's amount of sodium and the calories about half of what he burned; that's not unreasonable. Most people can't tolerate the "flavor fatigue" of nothing but gels for that long. The gels each contain less than 0.5g of protein (specified as alanine,valine, isoleucine and leucine, so incomplete protein), but over a day could be as much as 30 grams; most ultrarunners want more than that, for a number of reasons. Maltodextrin enters the bloodstream faster than table sugar (sucrose) or glucose, but keeps osmolality down, which is why it's popular in these preparations.
The standard I keep hearing is "100-200 calories and an S-Cap electrolyte every hour." One burns about 100 calories per mile, so few people consume as much as they burn (Yiannis Kouros is the famous counter-example). The thing is: one has to become accustomed to eating while running and one should do the same thing in training as in racing; it's the people who try something new in a race that have the most problems - as I know from experience. S-Caps (from Succeed) contain 341 mg. of sodium each, so one an hour for a day would be 4800 mg, which is high for those not running ultras, but could be high or low for a competitor, depending upon their usual consumption.
Every runner is an experiment of one. The advice you'll get is "find what works." Some runners can eat anything with no problems and some are puking their way from one aid station to the next, no matter what they eat.
As for the science, Tim Noakes' book "The Lore of Running" has a hundred pages or so about the science of nutrition for ultras. It has led me down many, many bad avenues, however.
For races under 6 hours, carboloading is probably important and what's consumed during the race unimportant.
You're going to have a calorie deficit as you go and if you go fast enough (and especially if there's hills), you're going to run out of glycogen, so you need to restock carbohydrates. You won't recover the lost muscle glycogen, but recovering liver glycogen means eating (or suffering and quitting). You're going to lose fluid, sodium and potassium, so these need to be replenished, though bodily stores of potassium are usually sufficient. Lost magnesium and calcium should not be a consideration until after the race.
Drink before you're thirsty. Eat whatever seems agreeable. It's better to have too few electrolytes than too many, because you can always ingest more, but it's hard to get rid of the extra. Drink enough that you're urinating every few hours. Try some salty foods on occasion at aid stations; if they taste good, you probably need sodium; otherwise they'll start to taste bad. Eat real food - as close to what you normally eat during a day and as close to when you eat each day; this will take care of everything else you need.
If things go wrong, first try water. Then try salt. Then try real food. Then you can start with whatever weird thing someone suggests, because you have nothing left to lose.
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