Practically speaking, any person could starve themself (short of death) and lose weight. In almost all cases there is no magic to storing more energy than you need.

Practically speaking any person cannot maintain that for significant length of time. Dieting has like a 99% fail rate by year 2. It’s hard to maintain that for many people — your body will keep you in starvation mode, keep you hungry and hang on to every calorie received.