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Comment by typon | Hacker News Reader

How much weight did he lose? It's quite amazing how calorie dense our energy storage mechanisms are.

Someone on Twitter calculated about 55,000 calories burned. Not sure if he had things to consume while running - but 8 - 10 lbs of fat burned in one day is wild to think about.

Definitely had things to consume. I don’t think you could go through this kind of effort on your energy storage only. I don’t think it can be mobilised that fast. Hydratation probably is a major concern too.

That seems way too high. A rough ballpark of energy expenditure while running is 1000 kcal per hour. Strava has the activity at 16,751 kcal.

Dang, that would be SO impressive... <1000 calories an hour would mean he is running SUPER efficiently from a body perspective, but of course, with the right hydration, nutrition, and temperature it is all possible to burn less calories.

I don't know about that, it's probably not super precise but an hour running is 600-700 kcal burned, reported by Garmin Connect

Whether you walk it or run it, a mile is about 100 calories. So, give or take, ~20,000 calories. Divide by 3500 calories/lb. and he burned five pounds of fat he probably didn't have to spare. But not so fast, he was also consuming calories along the way, and consuming a lot.

So calculating the net burn would be quite difficult. But the gross burn was probably about five pounds/2.25Kg.

IIRC, a gallon of gasoline is about 37,000 calories. So that's a lot of energy he utilized, all through his body burning fat and carbs!

Not sure if he had things to consume while running

Oh, he had things to consume. I ran 16 miles on hilly terrain on Saturday, and just for that I brought about 500 calories with me (not all consumed, some was "just in case").

It has been said that your liver stores about 2000 calories of glycogen. Divide by ~100 calories/mile, and now you know why marathoners hit "the wall" at about 20 miles if they don't chomp on some calories along the way.

So a probably safe comparison is Ironmans or Ultramarathons (100 milers go for 17-18 hours for the top finishers). Usually you have to put in a huge amount of carbs per hour (50-80g/hr) and a high amount of calories (250-400 cal/hr). Hydration is obviously also very important and getting sodium will be key (1000mg/hr). Outside of that you can generally limit your body's usage of fat stores though at this length and time it is probably inevitable.

I would suspect that if properly hydrated and consuming calories (no easy feat after 12 hours because the stomach does really go to shit) maybe 600 net calories an hour (-1000/hr + 400/hr from nutrition) = 4-10 lbs (@3000 cal/lb).

Range provided because I suspect my calculations are a little off and I'm underestimating the calories burned and probably overestimating the ability to consume that many calories/hour.

TLDR: Probably 10 lbs if they are properly hydrated and fed (which this appears to be a VERY well supported achievement)

I wonder if losing weight over the course of the run itself means that it got easier for him to move near the end (of course offset by the tiredness/fatigue) - I wonder if the effect did slightly cancel out?

I wouldn't think it would be helpful to lose weight, the issue really is that turning fat stores into calories is quite slow (for how many calories he is consuming) and it can't be relied on as a source of energy so you just end up more tired I think.

You need some amount of weight for muscle to push your body forward and I don't know that there is a big aerodynamic or energy advantage to sacrificing weight for that.

It's very hard to comsume 600 calories an hour whilst long distance running. A good thing to aim for is 200 calories as that's probably about the max your body can digest whilst running.

However, this guy is clearly superhuman so who knows :D

I had the estimate at 400 calories in my post (which is on the high end for sure), which is what I know some Ultraman and ultramarathoners aim for in at least the first half or bike legs of their race. I believe 200 is enough for amateur runners, but I know professionals really load up since the calories from carbs are definitely more efficiently utilized than fat stores.

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