Intestinal flora, normal of human intestinal tractmicroorganism, such as Bifidobacterium, Lactobacillus, etc., can synthesize a variety of vitamins necessary for human growth and development, such as B vitamins (vitamin B1, B2, B6, B12), vitamin K, niacin, pantothenic acid, etc., and can also use protein residues to synthesizeessential amino acid , such as phenylalanine, valine and threonine, and participate in the metabolism of sugars and proteins, while also promoting the absorption of iron, magnesium, zinc and other mineral elements.These nutrients play an important role in human health, and will cause a variety of diseases if lacking.
There are 10 trillion bacteria living in the human intestinal tract. They can affect weight and digestive ability, resist infection and the risk of autoimmune diseases, and control the response of the human body to cancer drugs.[1]
[2]According to the number of culturable bacteria, there are more than 400 kinds of bacteria in the intestinal flora, which can be divided into dominant microflora and sub dominant microflora.
① Main (dominant) flora: refers to the bacteria with a large number or population density in the intestinal flora, generally more than 10~10cfu/g, including specific anaerobic bacteria such as Bacteroides, Eubacterium, Bifidobacterium, Ruminococcus and Clostridium, usually belonging to the original flora.Dominant flora is a flora that plays a physiological function on the host, which affects the function of the entire flora to a large extent and determines the physiological and pathological significance of flora to the host.
② Secondary flora: the number is below 10~10cfu/g, mainly aerobic or facultative anaerobic bacteria, such as Escherichia coli and streptococcus, with large mobility and potential pathogenicity, most of which belong to foreign flora or passing flora.
Lactobacillus belongs to the secondary flora in quantity and has a high content in the ileum, but it has more important functions, so it belongs to the dominant flora in function.
The dominant flora is closely related to the characteristics of microhabitats. The dominant flora dominated by anaerobic bacteria generally lives in microhabitats with low clearance rate and rich nutrition, such as colon, so the flora density and diversity are high;While facultative or aerobic flora generally live in microhabitats with high clearance rate, such as the proximal end of the small intestine, its flora density and diversity are low. Because of the low flora density, it is difficult to be called "dominant flora";Acid tolerant and acid producing bacteria become the dominant flora in acidic microhabitats.The change of microbiota can replace the dominant flora in the flora. For example, when constipation occurs, the dominant flora in the stool is mainly gram-negative anaerobic bacteria, when chronic diarrhea occurs, the common gram-positive bacteria are the dominant flora, and when severe acute diarrhea occurs, the dominant flora in the stool is pathogenic bacteria or some facultative/aerobic bacteria.In the intestinal tract, although obligate anaerobes are the main flora and occupy the advantage, these flora also depend on the existence of secondary flora such as aerobic bacteria or facultative anaerobes, because the latter consumes oxygen in the process of proliferation to ensure the growth conditions of the former.A physiological combination of intestinal flora is beneficial, while a pathological combination of intestinal flora is harmful.
More than 99% of the microorganisms in the human intestinal tract are bacteria, and there are about 100 trillion of them, 500 to 1000 different species.These large numbers of bacteria can be roughly divided into three categories: beneficial bacteria, harmful bacteria and neutral bacteria.
probiotics , also known as probiotics, mainly various bifidobacteria, lactobacilli, etc., are indispensable elements for human health. They can synthesize various vitamins, participate in food digestion, promote intestinal motility, inhibit the growth of pathogenic bacteria, and decompose harmful and toxic substances.
Once the number of harmful bacteria grows out of control, it will cause a variety of diseases, produce carcinogens and other harmful substances, or affect the function of the immune system.
Neutral bacteria, i.e. bacteria with dual functions, such as Escherichia coli, Enterococcus, etc., are beneficial to health under normal circumstances. Once the proliferation is out of control, or transfers from the intestinal tract to other parts of the body, it may cause many problems.
Human health is closely related to the structure of probiotics in the intestinal tract.In the long-term evolution process of intestinal flora, through individual adaptation and natural selection, different species of flora, flora and host, flora, host and environment are always in a state of dynamic balance, forming an interdependent and interdependent system. Therefore, under normal circumstances, the structure of flora is relatively stable, and it is not pathogenic to the host.
Some studies have pointed out that 70% of healthy people have probiotics in their intestines, 25% of ordinary people, and 15% of people with constipation, while only 10% of cancer patients have probiotics in their intestines.
physiological function
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Physiological function of beneficial flora:
If the intestinal flora is dominant, the intestinal mucosa is pink, indicating that the intestinal environment is quite good.
The food decomposed and digested in the stomach is absorbed by the small intestine and sent to the large intestine as a viscous substance.Then after 18 hours of absorption of water and minerals, it will become feces easy to excrete.When the intestinal environment is good, the stool is moderate in hardness and defecation will be smooth.
2. Mild peristalsis, which can smoothly discharge feces
By the peristalsis of the intestine, the feces are slowly pushed to the anus.If the peristalsis is too fast or too slow, it will affect the composition of feces, leading to constipation or diarrhea.If the intestines are clean, the speed of peristalsis is quite regular, and feces can be discharged smoothly.
3. Helps the synthesis of vitamins
Good bacteria such as Bifidobacterium can maintain skin health, and have the function of synthesizing vitamins B1, B2 and B6, which are helpful to heat generation, and vitamin K, which is related to hemostasis and bone formation.With a healthy gut, good bacteria will continue to multiply and vitamin synthesis can proceed smoothly.
4. Rapid discharge of harmful substances
Healthy intestines are not completely free of bad bacteria, and harmful substances will be produced.Of course, it also includes food chemical additives or substances that cannot become nutritional ingredients.As long as the intestinal environment is good, these substances are discharged from the body before they begin to harm the body.
5. Avoid the invasion of pathogenic bacteria
Good bacteria such as Bifidobacteria can stimulate and improve the immune function of the body, and pathogenic bacteria such as those that are prone to food poisoning, such as lactic acid drinks or health food containing good bacteria, can inhibit the propagation of pathogenic bacteria in the intestine because of their acid fearing characteristics.
In addition to the above functions, intestinal beneficial bacteria have nutritional effects on human body, such as diabetes, hypertension, hyperlipidemia, etc.B vitamins and nonessential amino acids play an important role in human hair. When these nutrients are lacking, hair will fall off or become yellow, forked and easy to break.
Physiological function of harmful bacteria:
If the harmful bacteria flora "wins", the intestinal mucosa is rough, and the blood is not circulating and appears dark red.
1. Poor excretion and feces accumulation in the intestine
In order to help defecate, the degree of hardness of stool should be moderate, but unhealthy intestines are caused bydietary fiberThe feces are accumulated in the large intestine and cannot be excreted smoothly;Or it is the reproduction of bad bacteria that causes bacterial infection, resulting in diarrhea.
2. Creep too fast or too slow
If the intestines are not healthy, it may affect the intestinal peristalsis too fast or too slow, which will prevent the smooth excretion of feces.The feces will become too hard or too thin, which will eventually lead to constipation, and the flora passing through the intestines will therefore accelerate the reproduction, so the vicious cycle continues.
3. Hazardous substances
An unhealthy gut is an excellent place for bad bacteria to breed, and a large number of bad bacteria will causeAmonia, the generation of harmful substances such as sulfurized water and skatole.These substances are not only the source of fetid fart, but also accelerate the aging of intestinal wall, produce substances that cause cancer, and becomeColorectal cancerThe source of the disease.
4. Absorb harmful substances again
Harmful substances will not stay in the intestines obediently. They will follow the blood circulation throughout the body with the absorption of the intestines, causing fatigue, dry skin, headache, vomiting and other physical discomfort. Substances that can produce odor will be emitted through the blood, mouth or body.
5. Pathogens are easy to invade
In the unhealthy intestine, the amount of good bacteria such as lactic acid bacteria will become less, and the intestine is alkaline.In addition, the harmful substances produced by the bad bacteria reduce the immune function of the intestinal wall, leading to weakened sterilization in the intestine and easier invasion of bacteria or pathogens.
ecological equilibrium
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The dynamic balance between human beings and microorganisms is called micro ecological balance. The factors that affect its micro ecological balance include external environment factors and host factors.The external environment is mainly produced by changing the physiological function of the host, such as beneficial flora, by producing bacteriocin, antibiotics and their metabolites, as well as competing for nutrition and space to prevent the invasion of passing flora and maintain its stability.When the ecosystem is balanced, it can maintain the normal physiological functions of the host, such as nutrition, immunity, digestion, etc.Ecological imbalance can be caused by chronic diseases, cancer, surgery, radiation infection, irrational use of antibiotics, etc.
For those with intestinal microecology imbalance, they can eat more alkaline food containing dietary fiber, and can also supplement microecological agents such as ecobiotin, bifidobacteria or stachyose, so as to better regulate the health of intestinal microecology.
Distribution
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There are many kinds of microorganisms in the gastrointestinal tract of healthy people, which are called intestinal flora.Bacteria in human gastrointestinal tract can form a huge and complex ecosystem. There are more than 400 bacteria species in a person's colon.[3]
Most of the bacteria entering the stomach from the mouth are killed by gastric acid, and the rest are mainly gram-positive aerobic bacteria.The concentration of bacteria in stomach is less than 103 CFU/ML (CFU is colony forming unit).
The composition of intestinal flora is between stomach and colon.The flora in the proximal small intestine is similar to that in the stomach, but Escherichia coli and anaerobes can often be isolated.In the distal ileum, between anaerobic.
The flora in the proximal small intestine is similar to that in the stomach, but Escherichia coli and anaerobes can often be isolated.
In the distal ileum, the number of anaerobic bacteria began to exceed that of aerobic bacteria, among which Escherichia coli was constantly present, and anaerobic bacteria such as Bacteroides, Bifidobacterium and Clostridium were all in considerable quantity.
stayIleocecal valveIn the far side of the feces, the bacterial concentration increased sharply, and the colonic bacterial concentration reached 10.11~10.12 CFU/ml, accounting for almost 1/3 of the dry weight of the feces.Anaerobic bacteria are 10.3~10.4 times of aerobic bacteria.The main strains are Fecal Bacillus, Bifidobacterium and Eubacterium.
influence factor
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There are four main factors affecting the intestinal flora: human factors (intestinal acid-base, secretion of bile and digestive enzymes, intestinal peristalsis, secretion of intestinal mucus, intestinal epidermal detachment, etc.) and environmental factors (pressure, travel, etc.);Human diet (digestible food, indigestible fiber, drugs, etc.);Factors of bacteria themselves (adhesion ability, reproduction ability, nutrient demand, anti digestive enzyme ability of bacteria, etc.);Interactions between bacteria (nutritional competition, mutual inhibition, synergy, etc.).
The intestinal flora is in a healthy balance (the number of probiotics in the large intestine is 1000 to 10000 times that of harmful bacteria). Pathogenic bacteria or conditional pathogenic bacteria exist in a small number, and the toxic metabolites they produce are not enough to harm the health of the host.However, when the above four factors change dramatically, the number of beneficial bacteria in the intestinal tract decreases significantly, the number of harmful bacteria increases crazily, and the balance of intestinal flora is broken, the human body will have diarrhea, constipation, indigestion and other symptoms.If the balance of intestinal flora is broken, the health will be damaged.
Therefore, in order to ensure the normal daily operation of the intestinal tract, in addition to reasonable diet and normal work and rest in daily life, sufficient prebiotics should be added to multiply beneficial bacteria in the intestinal tract to keep the intestinal tract healthy.The survey data shows that the actual daily intake of prebiotics per capita is 2-8g/d, which is still a certain gap from the minimum daily intake of 15g.Therefore, ordinary people need additional supplement if they want to ensure that the intestinal tract needs prebiotics every day.[4]
Health Connections
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Cause obesity
State Key Laboratory of Microbial Metabolism, College of Life Science and Technology, Shanghai Jiaotong UniversityZhao LipingA study by leaders shows that,ObesityIt may be caused by bacterial infection rather than overeating, too little exercise or genetic factors, which may have a profound impact on the public health system, the pharmaceutical industry and the food manufacturing industry.[5]
After eight years of research by scientists around the world, this discovery in China explains the link between intestinal bacteria and obesity.Professor Zhao Liping, from the research team of Shanghai Jiaotong University, who carried out the research, said: "This is a very important phenomenon. This is the last evidence that bacteria cause obesity that was missing before." Scientists found human bacteria related to obesity, fed them to older mice, and compared their weight gain with mice that were not fed with bacteria.Although the latter was fed high fat food and prevented from exercising, they did not show obesity symptoms.
Other scholars who had no connection with the project soon commented on the potential impact.Professor David Weinkove, a biology lecturer at Durham University, said: "If obesity is caused by bacteria, it may be infectious, may come from some unknown environmental factors, or from parents. In the end, it may have nothing to do with behavior." Weinkove believes that Professor Zhao's research has opened the way for interventional treatment of obesity,Drugs may be developed for treatment.
Clinical weight loss
Xie Liwei, a researcher from the State Key Laboratory of Applied Microbiology in South China and the Institute of Microbiology, Guangdong Academy of Sciences, andZhujiang Hospital of Southern Medical UniversityChen Hong and Sun Jia, professors of Endocrinology and Metabolism Department, worked together as a team to study and reveal that the baseline characteristics of intestinal flora are the determinants of the weight loss effect of low carbohydrate diet (LCD).Relevant research was published in Microbial Spectrum on September 15, 2021.[11]
Autoimmunity
Researchers from Toronto Sick Children's Hospital found that early life exposure to gastrointestinal bacteria can help mice prevent autoimmune diseases.The study also revealed why women have a higher risk of autoimmune diseases such as multiple sclerosis, rheumatoid arthritis and lupus erythematosus than men.Relevant papers were published in Science on January 17.
This study identified for the first time the difference between normal intestinal microbes of male and female mice raised in the same environment, and confirmed that transferring male intestinal bacteria to females with high genetic risk can prevent autoimmune diseases.
The second unexpected finding was that it revealed the effect of intestinal microbial therapy on sex hormones.When young female mice were exposed to normal intestinal microbes from adult males, their testosterone levels rose.Subsequently, scientists confirmed that this hormone is crucial for intestinal microbiota treatment to prevent this disease.It was found that the sex of animals determines their intestinal microbial composition, and these microorganisms affect the level of sex hormones, which in turn regulate an immune mediated disease.[6]
Microecological imbalance of intestinal flora can lead to local immune activation and induce systemic immune response.[13]
Blood pressure regulation
One study found that short chain fatty acids (SCFAs) produced by intestinal microbiota may play a role in regulating blood pressure by acting on two major short chain fatty acid (SCFAs) receptors, olfactory receptor 78 (Olfr78) and Gpr41.Jennifer L. Pluznick and colleagues found that Olfr78 is expressed in the kidney and mediates renin secretion in response to short chain fatty acids (SCFAs), especially propionate.When propionate is given to mice, their blood pressure will decline significantly and rapidly in a dose-dependent manner, while mice that knock out Olfr78 are particularly sensitive to this effect, which suggests that the normal function of Olfr78 is to increase blood pressure and resist the hypotensive effect of short chain fatty acids (SCFAs).In contrast, mice lacking Gpr41 gene had no hypotension response to propionate, and this dose led to a strong hypotension response in wild type mice, which suggested that Gpr41 was involved in the response to propionate to reduce blood pressure.Reducing the intestinal microbiota biomass of Olfr78 knockout mice by giving antibiotics led to their increased blood pressure, which suggested that propionate produced by intestinal microbiota regulated blood pressure through Olfr78 receptor.The authors suggest that studying the intestinal microbiota and the crosstalk of the kidney cardiovascular system may help to better understand and treat hypertension.[7]
Treat allergies
Early microbial contact and stimulation can affect the development of immune system.Intestinal flora can regulate the immune function of the body by promoting the development of intestinal immune system, inducing T cell differentiation and other ways to keep it in balance, thus avoiding or reducing the occurrence of immune related diseases.The occurrence of allergic diseases is related to the underdevelopment of the body's autoimmune system and the imperfect immune regulation mechanism. The intestinal flora can affect the body's immune system and the flora distribution in allergic children is different from that in healthy children, suggesting that the intestinal flora is related to the occurrence of allergic diseases in children.Studies have reported that probiotics have positive significance in the prevention and treatment of allergic diseases, providing a new way for the prevention and treatment of allergic diseases.[8]
Fight against cancer
Researchers from the United States and France found in December 2013 that intestinal flora can also control the human body's response to cancer treatment drugs.
Researchers from Institut Pasteur and other institutions in France reported in the American journal Science that cyclophosphamide, a drug commonly used for cancer chemotherapy, can destroy the intestinal mucus layer and allow intestinal bacteria to enter the circulatory system. Some bacteria reaching the spleen and lymph nodes can promote the formation of immune cells, while the latter will attack cancer cells.But when the researchers killed the intestinal bacteria of experimental mice with antibiotics, the ability of cyclophosphamide to indirectly promote the growth of immune cells would be greatly reduced.
Another study by the National Cancer Institute of the United States, published in Science at the same time, showed that researchers selected cancer experimental mice receiving chemotherapy with a survival rate of 70% and killed their intestinal bacteria with antibiotics.As a result, the chemotherapeutic drugs taken by these experimental mice no longer worked, and their survival rate dropped to 20% after two months.
The researchers tested oxaliplatin, a drug used to treat colon cancer.This drug works best when the intestinal bacteria of the test subjects are in an ideal state.But when antibiotics are used to kill intestinal bacteria, the efficacy of oxaliplatin is greatly reduced.
Generally speaking, doctors often need to use a lot of antibiotics to prevent infection for cancer patients, but research has found that antibiotics may affect the efficacy of anti-cancer drugs.The two studies also showed that for different anti-cancer drugs, the types of intestinal bacteria that help them are also different.However, previous studies have found that some kinds of intestinal bacteria may also promote the development of intestinal cancer, and we should not blindly supplement intestinal bacteria.[1]
Heart disease
In August 2021, as one of the correspondence authorsVanderbilt University Assistant Professor of Medical CenterMariana ByndlossPublished on《science》According to a study of, a high-fat diet will destroy the biological characteristics of the intestinal lining and its microbial community, and promote the production of a metabolite that may lead to heart disease.[10]
autism
Research shows that,Autism spectrum disorder（ASD）It may be partly due to the difference in the composition of intestinal flora, which is mainly based on the fact that scientists have observed that some types of microorganismsautismIt is more common in patients.
But on November 12, 2021, the journal Cell Press（《Cells》）A published paper suggested that this connection may actually be the reverse: the difference in flora found in the gut of autistic children may be related to the restrictive diet related to autism, rather than the cause of its symptoms.The corresponding author of this paper is from the Mater InstituteJacob Gratten, the first author of the paper is from Gratten's teamChloe YapDoctor.[12]
Latest research
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In a meta-analysis in the journal BioEssays, researchers from the University of California, San Francisco, Arizona State University and the University of New Mexico concluded that these microbiota can affect the feeding patterns of their hosts through the vagus nerve.Vagus nerve is a nerve that extends from brain to intestines. Microbes like to play with it.[9]
The intestinal flora controls the host's diet pattern for survival and reproduction, as well as to eliminate the microbial competitors next door.The gut is the battlefield of these bacteria, and manipulating the host's brain to make it ingest specific food is their main weapon.Sometimes they even endanger the host by making the host eat harmful food.Research has found that people with insufficient diversity of intestinal flora (that is, one kind of bacteria kills other bacteria by manipulating the brain) are more likely to be obese.
The paper emphasizes that intestinal flora is not the only factor of obesity, but the authors do find that some studies show that microbiota may be infectious, including those bacteria that cause overeating.
Then why can't we immediately use a bunch of antibiotics to genocide those bacteria in our intestines?Well, the paper explains that these microbiota have such important functions as "nutrition intake and immune development", that is, they provide us with vitamins and minerals, and build our immune system as a reward for living in our bodies.These microbiota also help the host digest certain foods.People living in Japan have a special bacteria to help them digest seaweed.Some African children who eat sorghum stalks have bacteria that help them digest cellulose.
Fortunately, everyone's microbiota can be easily controlled through relatively simple diet changes.
If you are worried about the composition of your microbiota, please understand that it may only take a few minutes to change it through diet - this is the time required for the evolution of your intestinal microbiota, which is only 24 hours long - this is the time required for the intestinal microbiota to self rebuild after the change of diet.Changing the bacteria in your gut may help change your eating habits, and vice versa.
"Because people can easily manipulate the microbiota by using prebiotics, probiotics, antibiotics, fecal transplantation and diet changes, changing the microbiota provides us with an easy to operate solution to problems such as obesity and unhealthy diet that are difficult to solve by other methods." The authors wrote in a statement.
In addition to making life healthier, "taking action against microbiota may prevent and treat many diseases, including obesity, diabetes and even gastrointestinal cancer," said Aktipos. "We are just beginning to understand the importance of microbiota to human health."
