[hnuser1234]

As body mass increases, the caloric intake required to maintain said mass increases. Likewise, as body mass decreases the caloric intake required to maintain said mass decreases. Fat people need to eat like the not-fat version of themselves in order to both lose weight and maintain their new mass. If "balance" is 2400 calories for their fat body, resuming eating 2400 calories will lead to them becoming fat again.