Starvation Mode: How It Works

How do you define starvation mode?

the most simple explaination I can think of would be:

the prolonged state of nutrition that exists when calorie intake plus energy from body fat utilization cannot match metabolic energy needs. the body can only release so much FFA's from stored fat at any one time. Once you hit that level, your body needs to do something to close the gap. In the short term, the body can feed off glycogen stores, but those become depleted in a matter of days if they aren't replaced, so generally, the time it takes to enter starvation mode depends on the size of the gap between stored fat plus nutritional energy taken in and energy requirements of the body.
Once the threshold is crossed, the body changes hormone signals, which triggers the body to start canabalizing muscle mass at a higher rate, and if this state is sustained, and metabolic homeostasis cannot be reached, then organ function begins to be reduced as well.