First, as long as you take in 500 to a thousand calories a day, nothing going to happen. You won't loose a significant amount of muscle mass. Your body will store this energy as fat.Starvation mode occurs if you have no calorie to very little calorie intake intake for a few days. Starvation mode is your bodies last defense to keep you alive Your body will start using the fat first to provide energy because theire is protein in fat.ow long does it take for your body to go into starvation mode? I've been sick with a stomach flu and im getting 500 - 1000 calories a day.