Gut: The Inside Story of Our Body's Most Under-Rated Organ

by Giulia Enders

I’m sometimes shocked by the way scientists huddle behind closed doors to discuss their important research results, without informing the public about them at all.

Japanese researchers fed volunteers luminescent substances and X-rayed them while doing their business in various positions. They found out two interesting things. First, squatting does indeed lead to a nice, straight intestinal tract, allowing for a direct, easy exit. Second, some people are nice enough to let researchers feed them luminous substances and X-ray them while they poo, all in the name of science. Both findings are pretty impressive, I think.

Of course, the way we go to the toilet is not the only cause of haemorrhoids and diverticula. However, it remains a fact that the 1.2 billion people in this world who squat have almost no incidence of diverticulosis, and far fewer problems with haemorrhoids.

Alcohol can multiply the number of gas-producing bacteria by a factor of up to a thousand. In fact, some bacteria feed on alcohol (which is why rotten fruit tastes alcoholic). With a gut full of busy gas producers, a night on the town can lead to a morning chorus of the pungent kind. So much for the ‘alcohol is a disinfectant’ argument!

many people find they feel tired and sluggish after eating. The food has not yet reached the small intestine — it is still in the preparatory stages of digestion. We no longer feel hungry because our stomach has been expanded by the food we’ve eaten. But we feel just as sluggish as we did before the meal, and now we have to come up with the extra energy for all that mixing and breaking down. To achieve this, a large amount of blood is delivered to our digestive organs, and many researchers believe that post-prandial tiredness may also be due to the resulting reduced blood supply to the brain.

Other signs of appendicitis are pain when raising the right leg against a resistant pressure (get someone to push against it), lack of appetite, or nausea.

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 to go, but our body is deaf to such complaints. The simple reason for this is that human cells adore fat.

Those who are prepared to spend a little extra on cold-pressed (extra virgin) olive oil will be dunking their baguette in a soothing balm for their heart and blood vessels.

Lactose intolerance is not an allergy or a real intolerance at all, but a deficiency.

The most common food intolerance in Germany is a similar one. A third of all Germans have trouble digesting the fruit sugar fructose. In fact, a common children’s counting-out rhyme in Germany, comparable to the ‘eeny, meeny, miny, moe’ of the English-speaking world, translates as: ‘ate cherries, drank water, got tummy ache, went to hospital’!

what we label a food intolerance may in fact be nothing more than the reaction of a healthy body as it tries to adapt within a single generation to a food situation that was completely unknown during the millions of years of our evolution.

While our hunter-gatherer ancestors ate up to five hundred different local roots, herbs, and other plants in a year, a typical modern diet includes seventeen different agricultural plant crops, at most. It is not surprising that our gut has a few problems with a dietary change of that scale.

Faeces are three-quarters water.

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 fibre. The more fruit and vegetables you eat, the more faeces you excrete per bowel movement. Increasing the proportion of that food group in the diet can raise the weight of a poo from the average 100 to 200 grams, to as much as 500 grams per day. 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 colorants, or cholesterol.

As adults, we swallow somewhere between six hundred and two thousand times a day.

A piece of steak may easily be churned about for six hours before all of it has disappeared into the small intestine. This explains why we often fancy a sweet dessert after eating meat or fatty, fried foods. Our blood-sugar levels are impatient and want to rise quickly, and dessert provides a quick blood-sugar fix.

Everyone has heard their little housekeeper at work. It is the rumbling tummy, which, contrary to popular belief, does not come mainly from the stomach, but from the small intestine. Our tummies don’t rumble when we’re hungry, but when there is a long-enough break between meals to finally get some cleaning done.

If you were to X-ray the same hundred people while they were vomiting, the picture would be the same a hundred times over. The brain responds to the alarm, activates the area responsible for vomiting, and switches the body to emergency mode. We turn pale as the blood drains from our cheeks and is sent to the abdomen. Our blood pressure drops, and our heart rate falls. Finally, we feel that unmistakable sign: saliva, and lots of it. The mouth begins producing it in great quantities as soon as it receives information from the brain about the emergency that’s underway. This saliva is meant to protect our teeth from the corrosive effects of the gastric acid they are about to come into contact with.

Vomit that contains recognisable bits of food is almost certain to have originated from the stomach, and not from the small intestine. The smaller the particles, the more bitter the taste and the more yellow the colour, the more likely it is to be a salutation from the small intestine.

P6! This is an acupuncture point, which is now recognised by Western medicine as effective against nausea and vomiting. Its benefits have been proven in more than forty studies, including placebo-controlled trials. Doctors do not know how or why P6 works. The point is located two to three finger-breadths below the wrist, right between the two prominent tendons of the lower arm. If you don’t happen to have an acupuncture needle handy, you can try gently stroking the skin at that point, until symptoms improve.

the organ that is responsible for little brown heaps, and unbidden sounds and smells or all sorts. This is the organ that is currently forcing researchers to rethink its role; in fact, scientists are cautiously beginning to question the view that the brain is the sole and absolute ruler of 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 ‘pooing our pants’ with fear. We can’t get our ‘arse into gear’ if we don’t manage to complete a job. We ‘swallow’ our disappointment and need time to ‘digest’ a defeat. A nasty comment leaves a ‘bad taste in the 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. For example, they never end up in the visual cortex at the back of the brain. If they did, we would see visual effects or images of what is going on in our gut. 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. Any neuroscientists reading this will be up in arms when I roughly define the responsibilities of these brain regions as, respectively, self-awareness, emotion, morality, fear, memory, and motivation. 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. Scientists need to conduct more laboratory experiments to look more closely at this possibility.

95 per cent of the serotonin we produce is manufactured in the cells of our gut, where it has an enormous effect on enabling the nerves to stimulate muscle movement, and acts as an important signalling molecule.

Anyone who suffers from anxiety or depression should remember that an unhappy gut can be the cause of an unhappy mind.

Work on an atlas of human bacteria did not begin until 2007.

Of our entire microbiome — that is, all the micro-organisms that teem on the inside and outside of our bodies — 99 per cent are found in the gut. Not because there are so few elsewhere, but because there are simply so inconceivably many in the gut.

Our gut’s microbiome weighs around two kilos and contains about 100 trillion bacteria.

One person might have stronger nerves than another because she has a better stock of vitamin B-producing bacteria. Another person might be able to deal easily with bit of bread mould eaten by mistake, or yet another might have a tendency to gain weight because the ‘chubby bacteria’ in his gut feed him a bit too willingly. Science is just beginning to understand that each of us is an entire ecosystem. Microbiome research is still young, complete with wobbly milk teeth and short pants.

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

As unborn babies, we live in an environment that is normally completely germ-free — the womb. For nine months, we have no contact with the outside world, except through our mother. Our food is pre-digested; our oxygen is pre-breathed. Our mother’s lungs and gut filter everything before it reaches us. We eat and breathe through her blood, which is kept free of germs by her immune system. We are sheathed in an amniotic sac and encased in a muscly uterus, which is corked with a thick plug like a big earthenware jug. All this means that not a single parasite, virus, bacterium, fungus — and certainly no other person — can touch us.

No matter how many sloppy kisses we give the car window, if we are allowed to kiss and cuddle with our mothers regularly, we will be protected by her microbes. Breastfeeding also promotes particular members of our gut flora — breast-milk-loving Bifidobacteria, for example. Colonising the gut so early, these bacteria are instrumental in the development of later bodily functions, such as those of the immune system or the metabolic system.

There are many, many kinds of bacteria — some beneficial, others less so. Breastfeeding can help shift the balance towards the beneficial, and reduce the risk of a later gluten intolerance, for example.

Breast milk is so beneficial that a more-or-less well-nourished mother need not do any more than suckle her baby to ensure it is receiving a healthy diet. When it comes to the nutrients it contains, breast milk provides everything that dietary scientists believe children need in order to thrive — like the best dietary supplement ever. It contains everything, knows everything, and can do everything necessary for a child’s wellbeing.

It is now generally accepted that the first populations to colonise our gut lay the main foundations for the future of our entire body. Studies have shown the importance of those first few weeks of postnatal bacteria-collecting for the development of the immune system.

The initial contact experienced by children born by caesarean section is mainly with other people’s skin. They have to glean bacteria for their gut somehow, since their population will not develop from maternal microbes, like those of children born vaginally. They might end up with bacteria from Nurse Suzy’s right thumb, from the florist who sold Daddy that congratulatory bunch of flowers, or from Granddad’s dog. Suddenly, factors like the motivation of underpaid hospital cleaners become significant. Did they wipe down the telephones, tables, and bathroom taps with loving care, or a lack of conviction?

Three-quarters of newborn babies who pick up typical hospital germs are those born by caesarean section. They also have an increased risk of developing allergies or asthma.

In terms of our microbiota, we reach ‘adulthood’ around the age of three.

We are only now beginning to learn the impact that the belly-based bacteria community can have on an adult human. In this respect, scientists know more about bees than human beings. For bees, having more diverse gut bacteria has been a successful evolutionary strategy.

A person’s enterotype depends on the family of bacteria that dominates the microbe population of their gut. The choice is between families that bask in the glory of the names Bacteroides, Prevotella, and Ruminococcus. Researchers identified these enterotypes distributed among Asians, Americans, and Europeans, irrespective of age or gender. In the future, enterotyping may help doctors predict a whole range of characteristics, such as the body’s response to soya, nerve resilience, or susceptibility to certain diseases.

Mindful yoghurt manufacturers often use bacteria that produce more ‘dextrorotatory’ (right-turning) than ‘levorotatory’ (left-turning) lactic acids. Molecules of the two kinds of lactic acid are mirror images of each other. Feeding the human digestive system with levorotatory lactic acid molecules is like giving a left-handed pair of scissors to a right-handed person: they’re hard to handle. That is why it is a good idea to pick yoghurt from the supermarket shelves that says ‘contains mainly dextrorotatory (or right-turning) lactic acid’ on the pot.

How is this possible? Bacteria are able to make various fatty acids out of indigestible carbohydrates: vegetable-loving bacteria tend to manufacture fatty acids for the gut and the liver; others produce fatty acids that feed the rest of the body. Thus, a banana is less likely to make you fat than half a chocolate bar containing the same number of calories. That is because plant carbohydrates are more likely to attract the attention of bacteria that provide fatty acids to local customers like the liver. Chocolate, on the other hand, is more likely to attract the attention of the full-body feeders.

Several studies have shown that our satiety-signal transmitters increase considerably when we eat the food that our bacteria prefer. And what our bacteria prefer is food that reaches the large intestine undigested, where they can then gobble it up. Surprisingly enough, those foods do not include pasta and white bread.

The feeling of satiety generally comes from two sides: from the brain, and from the rest of the body. A lot can go wrong here. In obese people, the gene that codes for satiety may be defective, and such people simply do not get that full feeling after eating. According to the ‘selfish brain’ theory, the brain does not receive enough of the energy eaten as food, and so decides that it is still hungry.

But we need to take a step back and ask cautiously: Does the body always want to get rid of its cholesterol? It produces between 75 and 90 per cent of our cholesterol itself. And that takes a lot of work! One-sided media reporting has given cholesterol a bad name, making people believe it is only evil. That is quite wrong. Too much cholesterol is not such a good thing, but neither is too little. If it weren’t for cholesterol, we would have no sex hormones, no vitamin D, and a plethora of unstable cells.

And in Germany, for example, a toxoplasma scan is not part of the standard set of pregnancy examinations. If your gynaecologist starts asking strange questions like, ‘Do you own a cat?’ at your initial pregnancy examination, don’t brush it off as meaningless small talk — she’s clearly an expert in her field.

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.

The fascinating thing about cleanliness is that it is mostly in the head. A peppermint tastes fresh; clean windows look clear; and there’s nothing better than the lovely feeling of slipping into a freshly made bed after a hot shower. We like the smell of clean things. We like to run our hands over smooth, polished surfaces. We find comfort in the idea that we are protected from an invisible world of germs if we use enough disinfectant.

The tradition of the weekly bath did not really take hold until the 1950s. Then, typical families took their bath on a Saturday evening, one after another in the same bathwater, and hard-working Dad often got to go in the tub first.

Fear-driven hygiene involves either trying to clean everything away, or kill it off. We don’t know what it might be, but we assume the worst. When we clean obsessively, we do indeed get rid of everything — both bad and good. This cannot be a good kind of cleanliness.