Extended fasting is widely prevalent in many cultures, but I wouldn't consider those parts of the world as having eating disorders. Starvation in a bigger sense is a prolonged deficiency in nutrients and energy needs. Fasting doesn't have to be a set number of hours/days either. You fast every time you go to sleep.
Starvation mode is something most people do not understand. I can’t count the number of morbidly obese people I’ve heard tell me they need to eat 6 small meals per day so their metabolism doesn’t shift into starvation mode and they stop losing weight.
The few studies we have on actual starvation suggest that the body’s BMR does not change substantially until > 10 days without food.
Fasting and low carb diets have very similar effects, principally keeping insulin levels very reduced.
