It doesn't have to. Increase your exercise relative to your caloric intake, and reduced your caloric intake to the minimum needed given your increased exercise. Increase exercise intensity gradually. Do this 5 days a week for a year and I will give $500 if you don't lose several stones after that period of time.
Often, when people bring up this simple fact, lots of folks try to put excuses and variations of "it's not that simple", when actually yes it is.
It’s like saying people who want to stay awake when they are tired should just keep their eyes open.