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

by Giulia Enders

salad containing the same amount of calories but with a homemade vinaigrette or yogurt dressing will keep you feeling full for longer.

Feces are three-quarters water.

Whatever fluid is left in the feces belongs there. This optimum water content makes our feces soft enough to ensure our metabolic waste products can be transported out of our bodies safely.

A third of the solid components are bacteria. They are gut flora that have ended their careers in the digestive business and are ready to retire from the workplace.

Another third is made up of indigestible vegetable fiber. The more fruit and vegetables you eat, the more feces...

The remaining third is a mixed bag. It is made up of substances that the body wants to get rid of—such as the remains of medicines, food coloring, or cholesterol.

Examining the color of feces can provide a useful insight into the goings-on of our gut.

The enteric nervous system controls all processes that take place in the digestive tract, and it is extra-ordinarily autonomous.

If the connection between the enteric nervous system and the brain is severed, the digestive tract carries blithely on as if nothing has happened. This property is unique to the enteric nervous system and is found nowhere else in the human body—without

We close our mouth, since breathing must stop for swallowing to take place.

each act of swallowing involves more than twenty pairs of muscles.

Constipation results from a disconnect between the nerves and the muscles of the gut when they are no longer working toward quite the same goal.

psyllium seed husks and the rather more pleasant-tasting plum. Both contain not only fiber, but also agents that draw extra fluids into the gut—making the whole business smoother.

Without the presence of water, fiber binds together in solid lumps. Water makes them swell up into balls.

Pushing digested food back into a holding pattern even just a couple of times trains the nerves and muscles to operate in reverse gear. That can make it increasingly difficult to change gears back again. This is compounded by the fact that the longer the feces stay in the gut, the more time the body has to extract fluid from them, making the business ever harder. A couple of

rocking squat technique. Sitting on the toilet, bend your upper body forward as far as possible toward your thighs, then straighten up to the sitting position again. Repeat this a few times and it should begin to work.

Overfed or misplaced bacteria can produce gases, causing cramps and flatulence.

Since human beings can barely absorb sorbitol (or lactulose) into their bloodstream, it is often used as a sweetening agent. It then appears on food labels as E420, and this explains why sugar-free cough candies, for example, always include the warning, “Excessive consumption may have a laxative effect.” Some studies have shown that sorbitol has a similar effect to lactulose, but causes fewer side effects overall (no unpleasant wind).

we hold our brains responsible for everything we experience in life—we think up experiences of well-being, happiness, or satisfaction inside our own heads. When we are insecure, anxious, or depressed, we worry that the computer in our heads might be broken. Philosophizing and physics research are matters of the mind and always will be—but there is more to our self than that.

Scientists are cautiously beginning to question the view that the brain is the sole and absolute ruler over the body.

We humans have known since time immemorial something that science is only now discovering: our gut feeling is responsible in no small measure for how we feel. We are “scared shitless” or we can be “shitting ourselves” with fear. If we don’t manage to complete a job, we can’t get our “ass in gear.” We “swallow” our disappointment and need time to “digest” a defeat. A nasty comment leaves a “bad taste in our mouth.” When we fall in love, we get “butterflies in our stomach.” Our self is created in our head and our gut—no longer just in language, but increasingly also in the lab.

Signals from the gut can reach different parts of the brain, but they can’t reach everywhere.

Regions they can end up in, however, include the insula, the limbic system, the prefrontal cortex, the amygdala, the hippocampus, and the anterior cingulate cortex.

This does not mean that our guts control our moral thinking, but it allows for the possibility that the gut might have a certain influence on it.

This boils down to one of the basic questions of our existence: how intensely are we prepared to strive for something that we believe exists?

The vagus nerve is the fastest and most important route from the gut to the brain. It runs through the diaphragm, between the lungs and the heart, up along the esophagus, through the neck to the brain.

A gut that does not feel good might now subtly affect our mood, and a healthy, well-nourished gut can discreetly improve our sense of well-being.

When a gut is irritated, its connection to the brain can make life extremely unpleasant. This shows up on brain scans.

Stress is thought to be among the most important stimuli discussed by the brain and the gut. 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.

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.

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, good budgeting is always better than running up too many debts.

Stress of any kind activates nerves that inhibit the digestive process, which means we not only extract less energy from our food, we also take longer to digest it, putting the gut under unnecessary extra strain.

Really good psychotherapy is like physiotherapy for the nerves. It eases tensions and teaches us how to move in a more healthy way—at the neural level. Because the nerves of the brain are more complicated creatures than the muscles of the body, a trainer needs to have more creative exercises up his sleeve.

Hypnotherapists often use thought journeys and guided imagery techniques. These aim to reduce the intensity of pain signals and alter the way the brain processes certain stimuli. Just like muscles, certain nerves can become stronger with increased use.

More recently, depression researchers have also begun investigating another possibility—that such drugs may increase the plasticity of the nerves. Neuroplasticity is the nerves’ ability to change. It is nerve plasticity that makes puberty such a confusing time for an adolescent brain—so much is still being molded into shape.