Why is it that...?

well, it does. its just not healthy. and you don't need to necessarily stop eating altogether. just eat small portions. that's one of the biggest factors in an effective diet that no one wants to recognize. what your mother went through forced her to eat smaller portions of food. she didn't exactly starve herself for days, which is what they usually mean when they refer to 'starving' oneself (even if she was hungry all the time). exercise will help because you burn calories, but then you have to make sure you don't make up for those burnt calories....thus essentially you are starving yourself because you have burnt tons of calories and only eaten a few.