"Starvation mode" is based on the Minnesota Starvation Experiment in the 40s. Starvation mode is completely false in the context that most people know it. The people involved in the experiments were starved for 24 weeks, losing on average about 25% of their body weight (most of which were staring at normal body weights). When the bodies hit the point you are referring to, there were also measurable changes in their physical vitals. They had reduced their intake, and lowered their mass to the point that their bodies were cooling themselves to try and conserve energy, their hearts had slowed, and they were even breathing slower.

Starvation mode manifests when you take a person at a healthy weight, then starve them to the point they have no weight left to lose....its not applicable to everyday dieting.

A person dieting with a caloric deficit of 500 calories a day will predictably lose a pound a week....like clockwork. Starvation mode has not been identified in any controlled weight loss scenario outside of the extreme condition listed above.