The decision to start eating, what to eat, how much to eat, and when to stop, are all controlled in a tightly regulated system in the brain. Our brain gets signals from our body, from our stomach, digestive tract and stores of fat, and translates them into action, to eat or stop eating. It coordinates these commands with our environment. So that when we are hungry, we know where to get food, what types of food are available, and which foods are tasty and satisfying. You can think of the coordination of sensing when we need to eat and knowing where and with what to satisfy that need, as being controlled by two brains working as one. Integrated in a tiny part of our brain that acts as command central, the hypothalamus. You can think of the first brain as our metabolic brain. This brain responds to our bodies needs by communicating between our gut and our hindbrain. The part of the brain that acts without thought as a reflex to the signals it receives from other parts of our body. For example, our stomach and digestive tract have sensors that detect when our stomach is empty or stretched and the type of nutrients that are or are not available in our digestive tract. In other words, these receptors sense the quantity and quality of food in our gut and communicate that information via nerves and appetite hormones to the brain. In response our hindbrain determines when we should start eating and when we are full.
What we conceptualize as the second brain is a bit more complicated. We can think of this as our emotional and thinking brain that responds to needs beyond calories. It helps us form memories of food. Which ones we like and which ones taste bitter or rotten. Which ones we ate at a particular place or time, such as on a date or holiday event. As well as other characteristics about the food, it's smell, look and texture. It also assigns an emotional value to food. So that we get pleasure and reward from certain foods. When foods are pleasing we learn to like that food and the brain uses the same powerful pathways that respond to narcotic drugs to communicate that information. Foods that are rewarding motivate us to want that food. They are controlled by dopamine signals, the same chemical we release from gambling and sex. The emotional satisfaction we get from food is so strong that it can override our metabolic brain, or the signals our brain receives that tell us we're full. Researchers speculate that our powerful drive to get such satisfaction from food was wired into our biology to motivate our ancestors to leave the safety of their caves, walk for miles, and risk encountering predators or toxic plants. The interaction between these two brains is complex, and in many ways, overlapping. They're nature's way of making sure our bodies fend off starvation, which was the biggest threat to our survival as the human species for most of our time on this planet. Starvation is rarely a problem in our modern world. We are going to see how our appetite and energy control systems aren't adapted for working to our advantage in our current food environment. That is part of the reason we are seeing such rising rates of obesity.