Why do you get light sleep when fasting?

Scientists have discovered that orexin, a neuropeptide, controls our appetite and drives our biological instinct to find food. When glucose levels in the cerebrospinal fluid drop, orexin increases neuronal firing, making us feel hungry. Conversely, when we're full and blood sugar rises, glucose levels in the cerebrospinal fluid increase, and orexin suppresses neuron firing, preventing hunger. Interestingly, scientists have also found that orexin affects sleep quality. When glucose levels in the cerebrospinal fluid drop, orexin prompts us to wake up from sleep, activating our food-seeking instinct. This is why you may experience light sleep, nocturia, and poor sleep quality during fasting—your body thinks it's time to eat!