What is the most efficient way to take in calories during a run?

An ultra-marathon, marathon, and ironman events all seem to be very dependent on being able to replenish your energy reserves. Biking seems to allow you to eat anything, but running is different.

  • Are Gels + Gatorade + Water the only or best thing?
  • If so then why only sugar?
  • Running slow means more fat burning but no one seems to talk about adding fatty foods.
  • If sugar is key then why not breads or pretzels over higher GI sugar sources?
  • Is the body only able to process sugars during a run?
  • And proteins the third source of energy seems to be out of the picture completely; why wouldn't a little bit of protein help?
  • Why wouldn't the most efficient way include all three sources to some extent?

2 Answers 2


Ultra-runners end up with a very efficient fat-burning metabolism and a very good idea of what food works for them.

Fundamentally, you physically cannot take in enough calories to keep up with the energy expended so your body must switch to burning fat. (There is a maximum gastric emptying rate; combine that with the need for the fluids to be at the same concentration as human blood (or you get osmotic exchange and water goes where you don't want it) then you get a limit of about 200-300 calories/hour.

Ultra races have aid stations. The distances vary but every 5-10km or so is normal. What they offer is pretty standard: water, sports drink, chips, boiled potatoes and salt, oranges, peanut butter and jelly sandwiches. Lots of easy carbs and salt. There are often other things as well: chocolate cake, sometimes burgers or a hot dog. I grabbed a hot dog near the end of a 50km race; it was awesome!

I, and other ultra runners, often take the attitude of showing up at an aid station and finding out what the body wants. We eat that and then go.

Ultra runners also use sports drink. Normally quite specialized it's mostly a variety of simple sugars at 8% concentration + sodium, potassium, magnesium and calcium. For longer ultra, there's an argument that replacing 1% of the sugar with protein helps slow down muscle break down.

Many of the faster ultra runners will run with two hand bottles: one has water, the other the sports drink. When they feel their stomach is getting a bit over concentrated with the sports drink (common on hot days) they will switch to drinking water to smooth things out.

  • Its a dynamic thing; I was afraid of that but it adds to the challenge. Thanks Sarge!
    – Jason
    Jun 30, 2015 at 0:28

There's a swedish runner called Rune Larsson (2:18 boston marathon), had the swedish record on 100 km (6:43:36) for 22 years, ran 374 km in 48 hours, 263 km in 24 hours, basically a very experienced ultra marathon runner.

His take on food is that most runners are too scared of trying things outside the norm, you don't have to eat enormous amounts of pasta before a race and you don't have to eat the kinds of products you mention.

He was challenged to have "Smörgåstårta" (something like a swedish sandwhich cake) (http://www.oresundskomiteen.org/wp-content/uploads/2014/03/Sm%C3%B6rg%C3%A5st%C3%A5rta1.jpg) instead of the pre-run pasta, which he said worked great. Also eating regular sandwhiches while running apparently works great.

There's a myth that your indigestion isn't able to handle regular food because your blood is occupied with moving your body, which doesn't seem to be true, at least not for long distance runs.

There are theoretical arguments for eating fructose during a run, and for short distances, sure, might be helpful, if it works in reality. Try it?

Protein might be a problem, it takes a lot of energy to metabolize protein (something like 30% of the energy), which is why you might feel warm after eating large amounts of protein, so I would skip it frankly.

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