Limbic (LIM-bik) hunger is a name for what happens when your eating behavior conflicts with your long-term preference to eat less. The name “limbic” comes from the limbic system, the part of the brain that connects primitive drives, emotion, and memory. For primitive humans, eating a lot when there was food available was a great idea. The “sweet tooth” many people have may be nature’s way of encouraging us to seek out and eat fruit, because we need the vitamins the fruit contains. You can’t eat just one potato chip because of limbic hunger. Eating one chip triggers more appetite because primitive limbic signals tell our brains we should eat as much as we can while the food is available. This leads to more eating, connecting in a vicious circle that doesn’t stop until the bag of chips is empty. The ancient instinct takes control of behavior, ignoring higher thinking and preferences. Limbic hunger in a land of plenty causes one to eat too often and eat too much. Limbic hunger can be impulsive and stealthy. You decide to eat just one doughnut. A few minutes or a few hours later, in the middle of the second or the third doughnut, you remember your decision to eat only one. You chose to stop at one, but something let you reach out for that second or third doughnut. That something is limbic hunger overriding your willpower and your conscious preference to eat less. Somatic (so-MA-tik) hunger is the sensation of discomfort in the stomach area that is commonly called hunger or hunger pangs. Somatic hunger is the result of the interaction of many hormonal and nerve signals and incorporates more information than just whether the stomach is empty. By itself, this sensation can be unpleasant. As long as it stays out of the mind, it’s tolerable, like a sore ankle or a bruise. You may consider this sensation to be far beyond unpleasant and totally intolerable. Be assured, that can change. Nature is not stupid. If hunger alone were to incapacitate a hunter by being excessively distracting or intolerable, then the hunter would be unable to hunt and the species would have died off long ago. We’re built with more resilience than that. As time goes by on the Fast-5 plan, the sensation of hunger becomes less frequent, less intense, and much less distracting.
Humans evolved in an environment in which meals were likely a once-a-day event because it took hours, sometimes days, to hunt the wild game, then hours more to prepare it. The kill was consumed in a single sitting because there were no refrigerators to hold leftovers for a midnight snack or a later day. Several hours after the end of the meal, bacterial growth on the uneaten portion of meat could make the food sickening or inedible, sometimes even lethal.