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

by Giulia Enders

Each individual villus contains a tiny blood vessel — a capillary — that is fed with the absorbed molecules. All the small intestine’s blood vessels eventually come together and carry the blood to the liver, where the nutrients are screened for harmful substances and toxins. Any dangerous substances can be destroyed here before the blood passes into the main circulatory system. If we eat too much, this is where the first energy stores are created. The nutrient-rich blood then flows from the liver directly to the heart. There, it receives a powerful push and is pumped to the countless cells of our body. In this way, a sugar molecule can end up in a skin cell in your right nipple, for example, where it is absorbed and then ‘burnt’ along with oxygen. That releases energy which the cell uses to stay alive, with heat and tiny amounts of water created as by-products. This happens inside so many cells at the same time that the heat produced keeps our body at a constant temperature of 36 to 37 degrees centigrade.

Sugar is the only substance our body can turn into fat with little effort.

We use fat to coat our nerves — just like the plastic on an electric cable. It is this coating that makes us such fast thinkers. Some of the most important hormones in our body are made out of fat, and every single one of our cells is wrapped in a membrane made largely of fat. Such a special substance must be protected, and not squandered at the first sign of physical exertion. When the next period of famine comes — and there have been many over the aeons — every gram of fat in that paunch is a life-insurance policy. Our small intestine also knows the special value of fat.

Unlike other nutrients, it cannot be absorbed straight into the blood from the gut. Fat is not soluble in water — it would immediately clog the tiny blood capillaries in the villi of the gut, and float on top of the blood in larger vessels, like the oil on spaghetti water. So fat must be absorbed via a different route: the lymphatic system. Lymphatic vessels are to blood vessels as Robin is to Batman. Every blood vessel inside the body is accompanied by a lymphatic vessel — even each tiny capillary in the small intestine. While our blood vessels are thick and red, and heroically pump nutrients to our tissues, the lymphatic vessels are thin and transparent-whitish in colour. They drain away fluid that is pumped out of our tissue, and transport the immune cells which ensure that everything is as it should be throughout the body.

Plants construct different proteins than animals do, and they often use so little of a given amino acid that the proteins they produce are known as ‘incomplete’. When our body tries to use these to make the amino acids it needs, it can continue to build the chain only until one of the amino acids runs out. Half-finished proteins are then simply broken down again, and we excrete the tiny acids in our urine, or recycle them in our bodies. Beans lack the amino acid methionine; rice and wheat (and its derivative meat substitute, seitan) lack lysine; and maize, in fact, is deficient in two amino acids: lysine and tryptophan. But this does not spell the final triumph of the meat-eaters over meat-avoiders: vegetarians and vegans simply have to make sure they eat a varied diet.

There are plants that do contain all the necessary amino acids in the necessary quantities: soya and quinoa are two, but others include amaranth, spirulina, buckwheat, and chia seeds. Tofu has a well-deserved reputation as an alternative to meat — with the caveat that increasing numbers of people are developing allergic reactions to it.

We begin practising swallowing as unborn babies in the womb. We swallow up to half a litre of amniotic fluid a day during this test phase. If something goes wrong at this stage, no harm is done. Since we are completely surrounded by liquid, and our lungs are full of it anyway, we are at no risk of choking in the normal sense.

As adults, we swallow somewhere between six hundred and two thousand times a day. And each act of swallowing involves more than twenty pairs of muscles.

Emotions like fear or stress can reduce the ability of the smooth muscle to stretch, making us feel full, or even nauseous, after eating just a small portion of food.

Movement is the most extraordinary thing ever developed by living creatures. There is no other reason for having muscles, no other reason for having nerves in those muscles, and probably no other reason for having a brain. Everything that has ever been done in the history of humankind has only been possible because we are able to move. Movement involves not just walking or throwing a ball; it is also pulling faces, uttering words, and putting plans into action. Our brain coordinates its senses, and creates experience in order to produce movement — movement of the mouth or the hands, and movement over many kilometres, or over just a few millimetres. Sometimes we can also influence the world around us by

If the gut has to continue to forego energy in favour of the brain, its health will eventually suffer. A reduced blood supply and a thinner protective layer of mucous weaken the gut walls. The immune cells that dwell in the gut wall begin to secrete large amounts of signal substances that 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.

the purpose of the brain is to create movement — irrespective of whether you are a sea squirt searching for a comfy rock beneath the sea, or a human being striving for the best life possible. The aim of movement is to bring about an effect. The

Their ability to extract the maximum energy from everything and pass it on to us has led to the suspicion that they may be responsible for an increased tendency to gain weight.

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.

The aim is also not to produce a population of permanently happy people.

Our bodies are familiar with acid, from fruit and good bacteria (for example, the lactic acid bacteria in yoghurt). When the acid is not too strong and comes in combination with other nutrients, it gains the trust of our taste buds. Thus we like to include an acid component when we cook a pleasant-tasting meal — tomatoes in the sauce, a squeeze of lemon over the fish, a glug of wine over the frying onions. This well-placed pleasure is fascinating for anyone with an interest in microbes.