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

by Giulia Enders

flabbergasted.

These two sphincter muscles have to work as a team. When what’s left of our food reaches the internal sphincter, that muscle’s reflex response is to open. But it does not just open the floodgates and let everything out, leaving the outer sphincter to deal with the deluge. First, it allows a small “taster” through. The space between the internal and external sphincter muscles is home to a large number of sensor cells. They analyze the product delivered to them, test it to find out whether it is solid or gaseous, and send the resulting information up to the brain.

That means the sphincter and the surrounding muscles have been disciplined so often by the external sphincter that they become cowed. If communication between the two sphincters breaks down completely, constipation can result.

Even without such defecatory discipline, something very similar can happen to women during labor. Childbirth can cause tearing of the delicate nerve fibers that allow the two muscles to communicate with each other. The good news is that those nerves can heal and reconnect.

Irrespective of whether the damage was caused by childbirth or in some other way, one good treatment option is what doctors call biofeedback therapy. Biofeedback therapy is offered by some gastroenterologists or gastroenterology departments. It teaches the two sphincters to overcome their estrangement and get to know each other again. A machine is used to measure how efficiently the internal and

external sphincters are working together. If messages from one to the other get through, the patient is reward...

But what are fossilizing, calcium-containing substances doing in our saliva? Saliva is basically filtered blood. The salivary glands sieve the blood, keeping back the red blood cells, which are needed in our arteries, not in our mouth. But calcium, hormones, and some products of our immune system enter the saliva from the blood. That explains why each person’s saliva is slightly different. In fact, saliva analysis can be used to test for diseases of the immune system or for certain hormones. The salivary glands can also add extra substances, including those calcium-containing compounds, and even natural painkillers. Our saliva contains one painkiller that is stronger than morphine. It is called opiorphin and was only discovered in 2006.

When we chew, we produce more saliva and with it more of such analgesic substances, which explains why a sore throat often feels better after a meal and even minor sores in the oral cavity hurt less.

The fact that we produce so little saliva at night explains why many people have bad breath or a sore throat in the morning.

Certain messenger chemicals released by the body when we are full can also stimulate the areas of the brain responsible for tiredness. This tiredness is perhaps inconvenient for our brain when we are at work, but the small intestine welcomes it. It works most effectively when we are pleasantly relaxed. It means the optimum amount of energy is available for digestion and our blood is not full of stress hormones. The phlegmatic after-lunch reader is a more efficient digester than the stressed-out office executive.

When we eat too much sugar, our body simply stores it away for leaner times. Quite practical, really. One way the body does this is by relinking the molecules to form long, complex chains of a substance called glycogen, which is then stored in the liver. Another strategy is to convert the excess sugar into fat and store it in fatty tissue. Sugar is the only substance our body can turn into fat with little effort.

Glycogen reserves are soon used up—just about the time during your run when you notice the exercise is suddenly much harder work. That is why nutritional physiologists say we should do at least an hour’s exercise if we want to burn fat. It is not until we pass through that first energy dip that we start to tap into those fine reserves. We might find it annoying that our paunch isn’t the first thing to go, but our body is deaf to such complaints. The simple reason for this is that human cells adore fat.

But merrily drizzling your olive oil into the pan for frying is not such a good idea as heat can cause a lot of damage. Hotplates are great for frying up steaks or eggs, but they are not good for oily fatty acids, which can be chemically altered by heat. Cooking oil or solid fats such as butter or hydrogenated coconut oil should be used for frying. They may be full of the much-frowned-upon saturated fats, but they are much more stable when exposed to heat. Fine oils are not only sensitive to heat, they also tend to capture free radicals from the air. Free radicals do a lot of damage to our bodies because they don’t actually like being free, much preferring to bond with other substances. They can latch onto almost anything—blood vessels, facial skin, or nerve cells—causing inflammation of the blood vessels (vasculitis), aging of the skin, or nerve disease. That’s why you should always close the bottle or container of olive oil carefully after use and keep it in the fridge.

The animal fats found in meat, milk, and eggs contain far more arachidonic acid than vegetable fats. Arachidonic acid is converted in our body into neurotransmitters involved in the sensation of pain.

Oils such as rapeseed (canola), linseed, or hempseed oil, on the other hand, contain more of the anti-inflammatory substance alpha-linolenic acid, while olive oil contains a sub...

Beans lack the amino acid methionine; rice and wheat (and its derivative meat substitute, seitan) lack lysine; and sweetcorn is, in fact, deficient in two amino acids: lysine and tryptophan. But this does not spell the final triumph of the meat eaters over the meat-avoiders. Vegetarians and vegans simply have to be cleverer in combining their foods.

There are plants that do contain all the necessary amino acids in the necessary quantities. Two of these are soy and quinoa, but others include amaranth, spirulina, buckwheat, and chia seeds.

In 75 percent of the world’s population, the gene for digesting lactose slowly begins to switch off as they get older. This is not surprising, as by then we are no longer reliant on our mothers’ milk, or formula milk, to nourish us. Outside of Western Europe, Australia, and the United States, adults who are tolerant to dairy products are a rarity. Even in our parts of the world, supermarket shelves are increasingly full of lactose-free products.

The mechanism behind fructose intolerance is different once again from that involved in the digestion of gluten or lactose. The cells of people with hereditary fructose intolerance contain fewer fructose-processing enzymes. That means fructose may gather in their cells, where it can interfere with other processes. Fructose intolerance that appears later in life is thought to be caused by a reduced ability of the gut to absorb fruit sugars. Such patients often have fewer transporters (called GLUT5 transporters) in their gut wall. When they ingest even a small amount of fruit sugar—for example, by eating a pear—their limited transporters are overwhelmed and, as with lactose intolerance, the sugar from the pear ends up feeding the flora of the large intestine.

Thus, a long-unrecognized fructose intolerance can lead to depressive disorders.

Cigarette smoke stimulates areas of the brain that are also activated by eating.

This may lead to a sense of satisfaction, but it also tricks the brain into producing more gastric acid for no practical reason, as well as causing the sphincter between the esophagus and the stomach to relax. This is why giving up smoking often helps reduce reflux and heartburn complaints.

Almost half of us have experienced constipation when traveling. Particularly in the first few days of a trip, it is often difficult to go properly. This can be due to a variety of reasons, but in most cases it boils down to the simple fact that the gut is a creature of habit. The nerves of the gut remember what kind of food we prefer and at what time we prefer to eat it. They know how much we move around and how much water we drink. They know whether it is day or night and what time we usually go to the toilet. If everything goes according to plan, they complete their tasks without complaint and activate our gut muscles to help us digest. When we travel, we have a lot on our mind. Did we pick up our keys and turn off the iron? We might remember to take a book or some music to keep our brains happy, but there is one thing we always forget—that creature of habit, the gut, is also traveling with us and is suddenly torn from its familiar routine. We spend the whole day eating prepackaged sandwiches, strange airplane meals, or unfamiliar spices. At the time we would normally be enjoying our lunch break, we’re stuck in traffic or waiting at the check-in counter. We drink less than normal, for fear of having to go to the toilet too often, and dehydrate even more during the flight. And, as if that weren’t enough, we might also have to face a big fat bout of jetlag.

All this does not go unnoticed by the nerves of the gut. They can get confused and put the brakes on until they receive a

signal that everything is normal and they can start work again. Even when the gut has done its work despite the confusion, and signals to us that we should seek out the toilet, we add to its woes by suppressing the urge because it happens not to be a convenient time. Also, if we’re honest, travel constipation can often be caused by the “not my toilet” syndrome. Sufferers of this syndrome simply dis...

1. There is a certain foodstuff we can eat to nudge the gut wall into action: fiber. Dietary fiber is not digested in the small intestine and can knock on the wall of the large intestine in a friendly way to say there is someone here who wants to be shown the way out. The best results are produced by 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. It can take two to three days before their effect is felt. So, you can start eating them either a day before your trip or on the first day—whatever feels safer. Those with no plum compartment in their suitcase can buy dietary fiber in tablet or powdered form from their pharmacy or drug store. One ounce (30 grams) is an appropriate daily dose of dietary fiber. There are two kinds of fiber: water-soluble and insoluble. The latter is better at stimulating movement through the digestive system, but it can often cause stomachaches. Water-soluble fiber does not provide quite such a powerful push, but it does make the contents of the gut softer and easier to deal with. Nature’s design is rather clever: the skins of many fruits contain large amounts of insoluble fiber, while the flesh of the fruit contains more soluble fiber.

Other diseases affecting the bowel are different. During an acute phase of their condition, patients with a chronic inflammatory bowel disease like Crohn’s disease or ulcerative colitis may have real sores in their bowel wall. With these conditions the trouble is not that even tiny stimuli are transferred from the gut to the brain—their threshold is still high enough to prevent that. The problems are caused by the diseased mucus membrane of the gut. Like patients with irritable bowel syndrome, sufferers of these conditions also show increased rates of depression and anxiety.

There are currently very few—but very good—research teams studying how to make the threshold between the gut and the brain less porous. This is important not only for patients with intestinal problems, but for all of us. 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. 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 malai...

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 me...

It would also mean that our gut is capable of making us feel the negative effects long after the period of stress is over.

Dr. Michael Gershon

Bud Craig.

The vast majority of our immune system (about 80 percent) is located in the gut.

I do not know who was eating enough raw eggs in the 1930s to lead to the discovery of this connection. I do, however, know who might possibly end up eating so much avidin in the future that they could have problems with vitamin H—pigs who accidently roam into a field of genetically modified corn. Genetic engineers have created transgenic corn with a gene that produces avidin to make it less susceptible to insect damage during storage. When pests—or stray pigs—consume the corn, they are poisoned. When the corn is cooked, it is no longer toxic, just like a good hard-boiled egg.

Nicotine, for example, makes it through to the brain, where it triggers reward signals or a feeling of relaxed alertness.

Toxoplasmata are the reason your cat’s litter should be changed every day if there is a pregnant woman in the house (but not by her!), why raw food should be avoided by mothers-to-be, and why fruit and vegetables should always be washed. Toxoplasmata cannot be transferred from person to person. Infection can only come from the little residents of a freshly infected cat’s gut. But, as mentioned earlier, they can survive for a long time, even on the hands of cat owners. Once again, good old hand washing is the best defense.

Good for treating diarrhea. This is the number-one use for probiotics. Gastroenteritis (stomach flu) and diarrhea caused by taking antibiotics can be helped using various pharmacy-bought bacteria. They can reduce the length of such a bout of diarrhea by about a day. At the same time, unlike most diarrhea medications, they are almost free of side effects. That means they are particularly suitable for small children and old people. In conditions like ulcerative colitis and irritable bowel syndrome, probiotics can increase the intervals between diarrhea attacks or inflammatory flare-ups.