Gaining

I’ve thought of eating 10k in a day, but I haven’t done it...yet. I have eaten meals over 3k calories and I did gain five pounds in just a couple of days. I should qualify that, I’m old so I gain easily.

I’ve reached 10k a few times. I’m skeptical about the body’s ability to absorb that much in a day. I’ve certainly sustained 7-8k daily for a week at a time, and with spectacular results.

I did some web searching one time trying to find out how many calories we could process in a day, without getting any hard numbers. The closest I could find was that people can probably absorb up to around twice what their maintenance calories would be (so if at your current weight and lifestyle you'd need about 3000 calories a day to maintain your weight, your body could probably manage to process around 6000 calories in a day).

I'm pretty sure that had never been tested on people who were deliberately over eating for a while, nor for that matter people who are just really fat in general so needing higher maintenance calories. Still, it is a starting point for thinking about things like this. And it suggests that for most people more than 7k a day may not really add much to the gaining.

(gaining is about a lot more than just raw calories in per day, but still it is a decent first-order approximation)