I think the mainly part is correct, but 12 hours of running like 6-7k calories for an 150 lbs. person. As you get heavier it’s going to go up fast (and non linearly)—essentially any kind of extreme exercise is going to put an upper limit on your weight.

I’m unsure if your body can even process 10k calories in day. The basal metabolic rate for a 1000 lbs person isn’t that high.