'True hunger' as the natural hygienists have it is supposed to return after fasting 40 days or something, when your fat reserves are completely depleted and you look like a skeleton with paper-thin skin. Nobody recommends that anymore, especially not outside a clinical setting.
If you, however, mean that your body is genuinely asking for nourishment rather than your palate asking for enjoyment, you could have that simply by eating a slightly calorie-reduced whole-foods diet (as I explained in my other comment) and working out vigorously. Keep it that way be eating (somewhat) mindfully.
True thirst would be something similar, when all your fat is gone and the body has no source of H to make water from anymore. You'd be severely de-hydrated at that point and probably have damaged your brain through multiple mini-strokes (which you wouldn't notice, just the effect of lessened mental capacity later) permanently.
You'd also be in a dangerous situation where one false move could kill you. You'd need to be taken to a hospital to have you re-hydrated after your electrolyte levels have been checked. Maybe you'd need parental nutrition.. probably still have a good chance of dying.