Comment by libraryofbabel
3 years ago
> Combining this with the fact that Everest climbers are apparently eating 10K+ calories a day and then up to around 20K on summit day, I have to wonder how these facts jive...if they can really temporarily push the limit, for how long, etc.
An interesting source here is the Fiennes and Stroud expedition to cross Antarctica in 1992. Stroud (a physician) actually tested how many calories they were burning each day using the doubly-labeled water method, and at one point (ascent to the polar plateau) it was up to 11k. So it is definitely possible to temporarily push the limit - as the article acknowledges - but these are exceptional circumstances.
Another related extreme case was the first person to solo-ski to the north pole. They pre-loaded, mostly on olive oil, packing on tens of kg in body fat, all of which (and more) was gone by the time they were done. I don't recall the daily calorie expenditures but it was gigantic. They did this because there is some mechanical advantage carrying a good chunk of one's energy supply directly on your own bones rather than towing it in the sled.
Fiennes and Stroud lost about 25kg each crossing Antarctica; I don’t know if they pre-loaded beforehand (hopefully they did, losing that much!) but they certainly ran a deficit as a strategic trade-off against their sled weight. Hauling a kilo of fat on a sled is definitely less efficient than carrying it on your own body.
Supposedly their calories during the expedition were primarily from butter, which they mixed into every food and even ate on its own. Apparently you get used to it.