We have an extensive network of nerve cells (neurons) lining our guts – some call it ‘the second brain’. This nervous system contains about 100 million neurons, more neurons than the spinal cord or the peripheral nervous system (sensory and motor nerves relaying impulses all over the body). The second brain consists of sheaths of neurons embedded in the long tube of our gut, from the esophagus to the anus, It gives the necessary stimuli for mechanical mixing of food in the stomach, breaking down particles, chemical processing, and rhythmical muscle contractions that move food down the intestinal tract. We can feel the inner world of our gut when we pay attention, especially if it gives us pain from malfunction (think of the cramps of dysentery, the discomfort of gas or the pain of appendicitis). Think of ‘butterflies in the stomach’ when you are anxious, or in love, or a ‘knot’ in your midsection when you are asked to do something you don’t want to do! Sudden fear, often felt in the belly, will stop digestion to route blood to your muscles for flight or fight. These feelings can come on before the brain in your head has understood the situation. The second brain works fast!
The second brain makes many neurotransmitters, just like the brain in our heads. Over 80% percent of the body’s serotonin is located in the gut, where it is made from tryptophan (an amino acid found in the proteins we eat). Serotonin regulates intestinal movements. If irritants are present in our food, gut nerve cells release more serotonin, making the gut move faster to get rid of the noxious substance. It can also induce vomiting. Gut serotonin is regularly released into the blood stream, where it is taken up and stored by blood platelets, and used to help in the clotting process when a cut or wound occurs. Serotonin is also important in the regulation of mood, appetite, sleep, muscle contraction and some cognitive processes.
The SSRI antidepressants (Prozac, Paxil, Zoloft, Celexa, Lexapro and others) increase serotonin levels and are highly effective for some people to alleviate depression and anxiety. However they can also can affect the gut and bone strength. Some, but not all, users have abdominal symptoms with these drugs. Serotonin’s role in bone strength is under study - bones get weaker in the presence of more serotonin. Users of SSRIs have been shown to have greater rates of bone loss than average, and should be extra careful to protect their bones with exercise, vitamin D and special medications if needed.
In addition to serotonin, the brain in the gut also makes the neurotransmitters dopamine, glutamate, norephinephrine and nitric oxide, and two dozen small brain proteins, called neuropeptides. Endorphins, that relieve pain, are also made in the gut, as well as tranquilizing substances. The food-mood connection is real.
You can keep your gut happy and healthy by some simple daily habits. Take a probiotic every morning (keep it refrigerated) to ensure a predominance of healthy bacteria in your colon. Eat plenty of simple plant food to ensure good levels of fiber, vitamins, minerals and other plant nutrients. Go for dried figs, dates or bananas instead of cake and candy. You know the rap! Have you tried dried bananas? Wow!
Sadja Greenwood, MD, MPH back columns on this blog. Leave me your thoughts.