I was watching Everest (2015) on the weekend and was wondering what the mountaineers do for sustenance on the day they attempt to summit. It appeared they left around midnight, aiming for a 2pm summit, returning to camp after dark. So even if things went well, they would be looking at 24 hours of climbing.
What would they carry for sustenance?
In 1996, they seemed to enjoy chocolate bars and candies.
From some of the accounts of the infamous 1996 season related by the 2015 movie, apart for the classic soup, tea and fluids, we can consider "junk food" on summit day:
Matt Dickinson (the other side of Everest) eats Muesli and pistachio nuts.
Lou Kasischke (After the wind) was very fond of M&Ms (and write a few time his despise for oatmeal)
Jon Krakauer (Into thin air) eats also M&Ms and some candy bars.
Graham Ratcliffe (A day to die for) seems to enjoy a few Mars bars.
Ed Viesturs (No shortcuts to the top) advises to eat a few candy bars, like Twix and Snickers. He also mentions energy gels.
On the summit day, it's important to go as light as possible. Lunch, which you eat almost anytime during the day, can be as little as a candy bar or two - Snickers, Twix, and hard semisweet chocolate bars are my favorites. A typical energy bar would freeze like a rock [...] I've come to favor energy gels.
But mostly, at very high altitudes, they all say it's very hard to eat and to keep food inside.
Hot soup mostly, it does depend on the individual diets of the climbers, not everybody eats the same thing, but most carry hot soup with them.
Despite the massive amounts of energy needed to summit Everest, the truth is most climbers don't eat much on summit day, and that's simply because they don't have an appetite due to the high elevation. Many climbers have to consciously force themselves to try to eat and drink at the upper camps of Everest.
On summit day you're in the death zone, which means it is literally impossible for your muscles to fully replenish themselves. That's why they call it the death zone, your body cannot survive because basic body functions like digestion begin to shut down. Basically, there's no such thing as rest up there, your body can't rest, if you sit down you just slow down the rate of fatigue a little, but you don't recover any strength. It's unreal the amount of energy they burn up their too, they will be advancing one step for every five breaths they take, travel no faster than 100m/hr (that's metres per hour) and they burn just as many calories as someone running a marathon.
Hydration is a huge challenge as well, your body actually requires ~5L of fluids a day at high elevation, if you don't drink at least that much, then your body starts taking it from wherever it can, like your intestines, which makes it even more difficult to digest food. Most of your fluids are lost just through breathing, this is compounded by using oxygen, because they have to make the oxygen extra dry to prevent your breather and fittings from freezing up solid.
So for the most part the answer is hot soup. It's easy on the stomach, it gives you nutrients as well as fluids, and it warms you up. You can also consume it without taking you mitts off. Frostbite is a big problem up there, and it's not entirely because it's super cold (-20°C to -30°C mostly) it largely because you blood is so thick like syrup from secondary polycythemia that you effectively have the circulation of a diabetic with too much sugar in their blood.
From Tenzing's autobiography Man of Everest
We started pitching the highest camp that has ever been made. And it took us almost until it was dark. First we chopped away at the ice to try and make our sleeping-place a little more level. Then we struggled with frozen ropes and canvas, and tied the ropes around the oxygen cylinders to hold them down. Everything took five times and long as it would have in a place where there was enough air to breath; but at last we got the tent up, and when we crawled in it was not too bad. There was only a light wind, and inside it was not too cold to take off our gloves. Hillary checked the oxygen sets, while I got our little stove going and made warm coffee and lemon juice. Our thirst was terrible, and we drank them down like two camels. Later we had some soup, sardines, biscuits and tinned fruit, but the fruit was frozen so hard we had first to thaw it out over the stove.
May the 29th... On the 29th Lambert and I had descended in defeat from the col to the cwm. Down-down-down. At about three-thirty in the morning we began to stir. I got the stove going and boiled snow for lemon juice and coffee, and we ate a little of the food left over from the night before.
I don't have Hillary's account High Adventure to hand but I recall there was a lot of lemon drink and tinned fruit mentioned. The lemon drink was some sort of powdered mix that also contained sugar. Both men write about a constant thirst at high altitude and about how good the lemon drink was.
Up very high one never has an appetite - indeed, you have to force yourself to eat- but because of the thin dryness of the air there is often a terrible thirst. For this, in my experience, it is very bad to eat snow or drink cold snow-water, for this only seems to make the throat drier, and often sore. Tea, coffee, or soup are all much better. And, best of all, on this 1953 climb, was the powdered lemon-juice that we mixed with sugar and warm water. On the upper mountain we drank so much of it that I began calling us the "lemon-juice expedition."
Tenzing talks about the journey down and getting past the South summit;
At about two o'clock we reached the high tent, where we stopped and rested again, and I heated some sweet lemon-juice over the stove. This was the first drink we had had for hours, and it was like new life pouring down into our bodies.
It has to go down to all the High-Altitude diets, and not just specific to Mt. Everest. Anywhere above 23,000 feet / 7,000 meters most of the mountaineers lose their appetite to a considerable level. So, at that altitude losing weight is a common observation. Thats where the fats come in picture. Body starts consuming these bodily fats and worst case muscles too. With this a climber needs energy to carry on and the higher altitude, low oxygen environment reduces a climber’s appetite and interest in eating, making weight loss a common observation but a serious concern beyond a certain level.
Remember as we all know Digestion needs energy, and to sustain the much needed energy, you need to eat and digest it. So, intake of the food and fluids that provide the most energy with the comparatively lesser amount of digestive effort is the way to go while at higher altitude.
Mainly, the high altitude diet is not just for high altitude. When you know you are going to eat it at altitude above 7000m and don't want to loose out on a summit, you better make habit of that kind of a diet. You don't want to find yourself asking a sherpa at higher camps: "What is this thing?"
