[Creative Cultivation Program] The small world in the intestines is also full of blood and gore. How can we eat well to help intestinal probiotics take over?

The human heart weighs about 300g, the brain weighs 1.3kg, the liver weighs 1.4kg, and the intestinal flora weighs up to 1.5kg. Hundreds of trillions (1014) of bacteria, viruses, fungi, and protozoa are active in our intestines, making them the largest organ and the last one we pay attention to.

We always say that a good intestinal flora is good for health, but what is a good intestinal flora? How can we maintain a good intestinal flora? Before answering these questions, we must first understand the different roles played by intestinal flora and the love-hate relationship between them.

Most of them are diligent civilians, plus a few restless werewolves

Most of the current research and applications on intestinal flora focus on bacteria . For example, the common ingredients of probiotics are bifidobacteria and lactobacilli. One reason is that bacteria have the highest biomass in the intestine. The intestinal flora is 99% bacteria + 0.1% fungi + 0.8% archaea + a little bit of worms and viruses. The second reason is that bacteria are easier to culture and purify, and we have a more mature control over them.

The composition of each person's intestinal flora is different, just like your unique fingerprint. In biology, different types of intestinal flora are called enterotypes . Healthy intestinal flora are similar, while disordered intestinal flora have their own problems . The bacteria in the intestine can be roughly divided into symbiotic bacteria, conditional pathogens and pathogens according to their respective performance.

Symbiotic bacteria are the good guys in the intestines that work diligently to help us metabolize food, provide essential nutrients, and promote the development of the immune system. They basically have no ability to harm people, and cooperate with the host for mutual benefit and win-win results.

Conditionally pathogenic bacteria are typical fence-sitters. They live in peace with humans when the environment is suitable and nutritious. However, once a crisis occurs, such as the advent of antibiotics, damage to the intestinal mucosa, or a lack of nutrition, they show their bad side, clinging to the surface of intestinal epithelial cells and even expressing some toxins, causing enteritis, while leaving behind a sentence: "It's all for survival."

The content of pathogens is very low under normal circumstances, and most of them are food-derived. For example, when we have diarrhea after eating bad food, it is often because we have ingested too many Shigella dysenteriae, pathogenic Escherichia coli, and Salmonella in the food. Under normal circumstances, the symbiotic bacteria in our intestines can resist the replication and reproduction of these pathogens and viruses, allowing them to leave the same way they came in, and not giving them the opportunity to proliferate and do evil in the intestines. However, if the number of enemies is too large, or the symbiotic bacteria are killed by antibiotics, intestinal infections will occur. There are also some pathogens, such as Clostridium difficile, which usually exist in the form of spores in the intestines and are sealed by the symbiotic bacteria in the intestines. Only when the intestinal flora is disordered or most of the bacteria are killed by antibiotics, these Clostridium difficile have the opportunity to become active again, causing colitis and even threatening life. Death caused by Clostridium difficile is most likely to occur in elderly patients who are hospitalized for a long time. There are limited methods to control Clostridium difficile, and it is very easy to relapse, but some recent clinical trials have found that fecal microbiota transplantation or taking probiotics has a significant effect on eliminating Clostridium difficile.

Therefore, we often say that we should protect these beneficial symbiotic bacteria, or supplement probiotics in a targeted manner. When their components in the intestine are dominant, our intestinal flora is often in a stable and healthy state .

A complex relationship: competition? cooperation? predation? win-win?

Don’t underestimate the smallest and most primitive single-celled organisms. Out of the instinct of all living things - to survive and reproduce, they are constantly fighting for territory and food, and when necessary, they need to resort to cruel or clever means. Even we higher animals would call us experts!

Each microorganism has its own comfort zone . Some bacteria have high oxygen requirements, so they live in places with relatively high oxygen content close to intestinal epithelial cells; some are strictly anaerobic, so they are more suitable for living in the intestinal cavity in a nearly anaerobic environment. Some bacteria live in the mucus layer near intestinal epithelial cells because the polysaccharides there are more to their taste. Some bacteria are just a small ball or a short stick and have no ability to move. Some bacteria are covered with cilia or have long flagella. If the living environment is not suitable, they can go on a spontaneous trip at any time.

There are no eternal friends, only eternal interests. The world of intestinal flora is a naked exchange of interests, without any disguise. Bacteria that can metabolize complex carbohydrates must be followed by a group of younger brothers, waiting to use the monosaccharides and disaccharides decomposed by the big brother as their own energy source. Microorganisms that are good at using the same food are in fierce competition, competing for oxygen and energy sources. The most valuable ones are monosaccharides including glucose and fructose, as well as some important amino acids.

The main reason why these microorganisms have their own preferred foods is that they can express different types of carbohydrate-active enzymes (Cazymes). The more single-type enzymes expressed by bacteria, the less sugars they can use. If the enzymes expressed overlap with other bacteria, their situation will be even more difficult, because not only are there less energy available, but there are also more competitors. On the contrary, those bacteria that have several brushes in their hands and can easily metabolize various carbohydrates are more likely to survive. Moreover, they are often good at preserving their strength. When the sugar source is sufficient, they only use carbohydrates in the food. When the sugar source is insufficient, such as when the host decides to quit sugar or diet, they turn on the enzymes that metabolize sugars in the intestinal mucus layer. That's right, each of our intestinal epithelial cells is tightly attached to a layer of mucus, which is all composed of glycosylated proteins and secreted by a special goblet cell in our intestinal epithelium. There is no sugar in the food, and the bacteria can only eat the host's own sugar without any care. Therefore, a zero-sugar diet should be followed with caution. Even if it does not affect the thickness of the intestinal mucosa, disturbance of intestinal flora is inevitable. After all, many bacteria that utilize carbohydrates in food will starve to death.

Competition is accompanied by killing. Some intestinal bacteria can specifically secrete bacteriocin , and only target bacteria similar to themselves. Some protozoa can directly devour bacteria when they are short of energy and use them as a source of energy. Other bacteria can inject part of their own genetic material into other bacteria, which is the horizontal transmission of genes. Scientists still don’t understand why these bacteria do this. Could it be that they see that the situation is serious and they can’t save their lives, so they save a piece of genetic material? Or even try to transform others into themselves? Is it the distortion of human nature or the decline of morality behind this? Scientists need to further explore.

Although competition and cooperation seem to be going on all the time in the intestines, and the composition of the intestinal flora is constantly changing, this is actually a good state. In fact, the higher the complexity and diversity, the higher the resilience of the intestinal flora. Conversely, the more single the intestinal flora is, the easier it is to be destroyed. It's like there is only one kind of tree in a forest, so if the borers targeting it come, they will definitely destroy the entire forest.

What can we eat to ensure that the common people have an advantage?

After reading the above content, I believe everyone has realized the importance of food to the composition of intestinal flora. So how can we eat to benefit the beneficial symbiotic bacteria?

First, let's rule out a few wrong options. Even without considering the problem of intestinal flora, we know that high-fat and high-salt diets are harmful to the body, which can easily accelerate cardiovascular and cerebrovascular sclerosis, promote the occurrence of metabolic diseases, and increase inflammatory factors in the body. Unsurprisingly, they are also not conducive to the stability of intestinal flora, and are often directly related to intestinal flora disorders and enteritis.

In fact, foods high in dietary fiber are very popular with symbiotic bacteria, such as whole-wheat products, quinoa[1], and inulin. Polysaccharides in high-fiber foods, such as starch, can be fermented and decomposed into short-chain fatty acids (SCFA) by symbiotic bacteria. Short-chain fatty acids are popular metabolites that play a positive role in the development of human immune cells, resistance to pathogens, neurological diseases, metabolic diseases, etc. I will not expand on this here, and can explain it separately later. High dietary fiber also helps to increase the diversity of intestinal flora.

Another diet that has received great acclaim is the Mediterranean diet[2], which is rich in vegetables, fruits, fish, whole grains, beans, nuts, and olive oil (unsaturated fat). This type of diet can improve the diversity of intestinal flora and intestinal homeostasis, especially increasing the content of probiotics such as Bacteroides, Lactobacillus, and Bifidobacterium. In addition, consuming the Mediterranean diet can improve inflammation and oxidative stress in the human body.

Other foods that are beneficial to the diversity of intestinal flora and the increase of symbiotic bacteria include fermented foods, plant proteins, unsaturated fatty acids, etc. Regulating intestinal flora by changing the composition of food has become a means for doctors to provide auxiliary treatment for patients with enteritis, obese patients or diabetics. If you often have intestinal disorders, you may also refer to the above healthy diet and make changes. In addition to the content of diet, many of our lifestyles and living habits, such as exercise, regular diet, smoking, etc., will affect the composition of intestinal flora.

This article is produced by the Science Popularization China-Creation Cultivation Program. Please indicate the source when reprinting