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

by Giulia Enders

Let’s agree for the sake of argument that there is at least a possibility that this group exists. Its proposed favorite food is the cell walls of plants.

Ruminococcus produces a substance called haem, which the body needs for many things, including producing blood.

One character who probably had problems producing haem was Count Dracula. A genetic defect has been identified in his home country, Romania, that results in symptoms that include a lack of tolerance to garlic, sensitivity to sunlight, and the production of red urine. This urine discoloration is caused by a defect in blood production that means sufferers excrete the unfinished precursors of blood production. Nowadays, those affected by the condition—called porphyria—are given medical treatment rather than the starring role in a horror story.

100 trillion tiny creatures reside in our gut and that cannot but have an effect on us.

Very few gut bacteria reside in the small intestine, where we break down our food for ourselves and absorb the nutrients from it.

The highest concentration of bacteria is found where the digestive process is almost finished and all that remains is for the undigested remnants to be transported away.

If the equilibrium is disturbed and large numbers of overconfident bacteria migrate to the small intestine, we have a case of what doctors call bacterial overgrowth.

It can be practical to keep your bacteria so close to the beginning of your digestive tract. Bacteria are rich in protein—so, from a food point of view, they are tiny little steaks. When they have finished their life’s work in the cow’s stomach, they slip farther down the system, where they are digested.

Our bacteria are too far down the system to provide this practical steakhouse service so we pass them out of our gut undigested.

Rodents keep their microbes as far down the system as we do, but are more loath to waste the bacterial protein they contain. Their simple solution is to eat their own feces.

Bacteria produce nutrients that are so tiny we can absorb them directly into the cells of our gut.

Yogurt is nothing other than milk that has been predigested by bacteria. Much of the sugar in the milk (lactose) has already been broken down and transformed into lactic acid (lactate) and smaller sugar molecules. That is why yogurt is both sweeter and sourer than milk.

Predigested milk (yogurt) saves our body some work—we just have to finish off what the bacteria started.

Mindful yogurt 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.

it is a good idea to pick yogurt from the supermarket shelves that states on the container: “Contains mainly dextrorotatory [or right-turning] lactic acid.”

Bacteria do more than just break down our food. They also produce completely new substances. Fresh cabbage, for example, is less rich in vitamins than the sauerkraut it can be turne...

Bacteria and fungi are responsible for the taste, creamy consistency of...

Lovers of wine or vodka appreciate the metabolic end product of yeasts—known as alcohol. The work of these microorganisms does not end in the wine barrel. Almost none of what a wine taster will tell you is actually to be found in the bottle. The wine’s bouquet, for example, develops so late because bacteria need time to do their work. They sit in waiting at the back of the tongue, where the process of transforming what we eat or drink begins. The substances they release during that process create the aftertaste so appreciated by the wine lover. And each connoisseur will experience a slightly different taste depending on the population of bacteria on their tongue.

The bacteria population of our mouth is only about one-ten-thousandth of the number that live in the gut,

While simple glucose and fructose are easily digested, many people’s guts start to flag when it comes to lactose, the sugar contained in milk. Their owners then suffer from a lactose intolerance.

Complex plant carbohydrates would flummox a gut if it were expected to have at the ready every enzyme needed to break them down. Our microbes are experts in dealing with these substances.

In the industrialized world, about 90 percent of our nutrition comes from what we eat, and we are fed about 10 percent by our bacteria.

if we are concerned about our weight, we need to think about more than just the big, fat calories we consume and remember that our bacteria are at the dinner table with us.

THE GUT FLORA might include too many bacteria that program a person for chubbiness. These chubbiness-inducing bacteria are efficient at breaking down carbohydrates. If the number of chubby bacteria gets out of hand, we have a problem.

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, and others produce fatty acids that feed the rest of the body.

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. The chocolate bar, on the other hand, is more likely to attract the attention of the full-body feeders.

Studies carried out on obese subjects show that they have less overall diversity in their gut flora and that certain groups of bacteria prevail—prima...

PATIENTS WHO HAVE metabolic problems, such as obesity, diabetes, and high blood-lipid levels, usually have slightly increased levels of infection markers in their blood, too.

doctors call these subclinical infections. If there is anyone who knows a thing or two about infection, it’s bacteria. They have a signaling substance on their surface that tells the body when to get infected.

But when bacteria appear in disadvantageous combinations, or when their host eats an overly fatty diet, too many of them can find their way into the bloodstream. The body then slips into low-key infection mode.

They also have an interesting effect on the thyroid gland. Bacterial infections hinder its function, causing it to produce fewer thyroid hormones, slowing the rate at which the body burns fat.

Unlike acute infections, which cause weight loss or even emaciation, subclinical infection causes weight gain. Bacteria are not the only possible cause of subclinical infections—hormone imbalances, too much estrogen, lack of vitamin D, or too much gluten-rich food have all been observed to have a similar effect.

Faced with the choice between two different dishes, we make the decision based on what we happen to fancy at that moment. The amount of our chosen dish that we actually eat is controlled by the feeling of satiety. In theory, bacteria have ways and means of influencing both those things.

Bacteria can produce particles that are small enough to make it through the coating of the blood vessels into the brain. Examples include tyrosine and tryptophan. These two amino acids are converted into dopamine and serotonin in the cells of the brain.

So the theory is this: our bacteria reward us when we send them a decent delivery of food. It feels pleasant and whets our appetite for the next meal. They do this not only directly by means of the substances they produce, but also by cranking up the body’s production of certain transmitters. The same principle applies to the feeling of satiety.

our microbes also need to be fed. They may seem small and insignificant by comparison with our body size—accounting for just 4½ pounds (2 kilos) of our body weight.

When we give up sweets, we eventually stop missing them so badly at some point. Is that because the gummy bear and chocolate lobby has been starved out? We can only speculate.

American scientists studying Maasai warriors in Africa had been surprised to find the levels of cholesterol in their blood were low, despite a diet consisting almost entirely of meat and milk. This excessive amount of animal fat did not cause high blood-lipid levels.

The bacterium added to the yogurt was Lactobacillus reuteri—in a form particularly resistant to digestion. Within six weeks, their levels of bad LDL cholesterol sank by 8.91 percent. That’s about half the improvement attained by taking a mild anti-cholesterol drug—but without the side effects. Studies using other types of bacteria lowered cholesterol levels by as much as 11 to 30 percent.

The most likely candidates we know of today are BSH genes. BSH stands for bile salt hydrolase.

Bile, which is stored in the gall bladder, is the body’s transport medium for fats and cholesterol. BSH allows bacteria to alter bile to make it work less efficiently.

If it weren’t for cholesterol, we would have unstable cells and no sex hormones or vitamin D.

Studies have shown a connection between too little cholesterol and memory problems, depression, and aggressive behavior.

Some scientists now support the theory that our gut microbiota can be considered an organ.

Just like the other organs in our body, this organ has an origin, develops along with us, is made up of a load of cells, and is in constant contact with its fellow organs.

there are more wild tortoises and lizards wandering around in Africa than Germany. Salmonella bacteria travel to our climes along with the chicken feed. How so? Well, they are part of the normal gut flora of reptiles. While the African farmer is working in the fields, a tortoise might merrily be doing its business in a sack of grain destined for Germany. After an exciting flight with a wonderful view over the clouds, the grain, along with its stowaway tortoise-poop bacteria, ends up in a German poultry farm, where it is eaten by a hungry chicken.

Once inside the bird’s gut, the Salmonellae can multiply, and they are eventually excreted. Since chickens have only one hole for all export goods, the egg cannot avoid coming into contact with Salmonellae in the bird’s feces. The bacteria are then found only on the shells of eggs—they only get inside when the shell is cracked.

Cheaply fed chickens are usually sent to large industrial slaughterhouses to meet their maker. Once they have been slaughtered and beheaded, they are dunked in huge tanks of water. Those tanks are like a wellness spa for Salmonella bacteria, complete with a colonic irrigation service for the chickens.

Even just ten minutes’ exposure to a temperature of 167 degrees Fahrenheit (75 degrees Celsius) is enough to see off all Salmonella bacteria. That’s why a carefully roasted chicken is not usually the culprit, but rather the lettuce leaves for the side salad, left to soak briefly in the same kitchen sink.

It takes between ten thousand and one million of these single-celled creatures to put us out of action.