Gut: The Inside Story of Our Body's Most Underrated Organ

by Giulia Enders

When the brain senses a major problem (such as time pressure or anger), it naturally wants to solve it. To do so, it needs energy, which it borrows mainly from the gut. The gut is informed of the emergency situation via the sympathetic nerve fibers, and is instructed to obey the brain in this exceptional period. It is kind enough to save energy on digestion, producing less mucus and reducing the blood supply. However, this system is not designed for long-term use. If the brain permanently thinks it is in an emergency situation, it begins to take undue advantage of the gut’s compliance. When that happens, the gut is forced to send unpleasant signals to the brain to say it is no longer willing to be exploited. This negative stimulus can cause fatigue, loss of appetite, general malaise, or diarrhea. As with emotional vomiting in response to upsetting situations, the gut reacts by ridding itself of food to save energy so it is available to the brain. The difference is that real stress situations can continue for much longer than minor upsets. If the gut has to continue to forego energy in favor of the brain, its health will eventually suffer. A reduced blood supply and a thinner protective layer of mucus weaken the gut walls. The immune cells that dwell in the gut wall begin to secrete large amounts of signal substances, which make the gut brain increasingly sensitive and lower the first threshold. Periods of stress mean the brain borrows energy, and, as any housekeeper knows,...