[mam2]

If you want a upper limit it's around 20000 calories. That's what eat people who go to the artic / antartic.

Honestly i think its WAY LESS oversimplified that people say it is. True you never know what you really ate, but if you note your average calories for a month, and then do +20% or -20% calories with the same type of food and same lifestyle you will get the exact weight loss / gain predicted from regressing on the first month.