Writing as someone who was a fat little kid and now a few years from retirement, weighs what he weighed in fifth grade and has been on a diet for almost 50 years:
“It’s not as simple as calories in, calories out.”
Perhaps not, but that’s a darned good part of it. Had I not made a major course correction, I doubt if I would have seen 45.
Truth is if you burn more calories than you consume you will lose weight. Some people may store more glycogen then others thus it will take longer for them to hit their fat reserves. Just like if you use 11 gallons of gas per week and only put in 10 per week eventually you will run out of gas.