What happens when your body goes into "starvation mode"?

Loss of muscle: Starvation mode is restricting calories so much (eating less all day or just 1x/day) that your body thinks the famine is coming. To protect itself and have enough energy for the day, it starts to break down muscle, not fat. Loss of muscle mass equates to more fat and a return of the weight. Weight loss is most effective when you lose only fat, not muscle.