At 7,500 calories per kg you would therefore lose 82,500 calories in one month to lose 11kg. Assuming a generous 31 day month this is 2,661 calories per day. Therefore the required caloric deficit for the day is larger than the total calorie intake meaning no calories would have to consumed to achieve this weight loss.

So how could this have been achieved? It could partly be inaccuracies in weighing, difference in body weight from food contents in digestive tract, water contents etc. The alternative is an increased energy expenditure which could partly account for it. Of note, generally consuming less than 1200 calories a day regularly is thought to be harmful on the basis that it is difficult to get minimum necessary nutrients in this time.

If I have made a mistake in my calculations, someone let me know.