Where does this 1200 number come from ?

My brother asked me just a week ago the same thing, every activity you do burns energy, the more active you are the more you will burn on top of your BMR ( and this varies/depends on gender, weight and height ), honestly i'm eating around 3500-4000 cals a day right now, but seeing as how i'm burning through 5000-5500 a day it's no problem. Just have to maintain a deficit.
Typically i eat around 5 or 6 times a day, keeping the bulk of my intake for late in the evening when i know i will have my cravings, i probably don't go more then 4 hours without having something, still i'm losing weight, i eat probably more now than i did when i was fat, it's just what i eat (cleanly) and regularly that keeps my metabolism burning all the time.
I should note i'm male but still i could not drop food intake so low, i love food and by varying my intake to match my activity level i have found something i can live with every day, i used to count cals religiously, now i just tally them in my head as the day progresses, have most things memorized.