How do you know if you're not eating enough? Your body will tell you. The Insider spoke with doctors who identified eight signs that indicate hunger, which could take a toll on your health. Moodiness is one of the first signs that you're not getting enough calories. It reportedly draws from prehistoric times. The Insider says that back then people "became anxious and stressed [...] which made you go out and kill a deer to eat." Additional signs of hunger include migraine headaches, feeling cold and hair loss.