Microbiota. How intestinal bacteria affect disease

    After a short break in connection with the May weekend, we continue a series of articles about the intestinal microbiota. We Atlas  already told how the microbiota , and  some bacteria live in the intestines of Russians . Today we share information on how some diseases are closely related to intestinal health.

    Illustration by Rentonorama

    Bacteria around us

    The practice of maintaining cleanliness of the body and home has existed at almost all times (the exception is the Middle Ages, but we remember what the unsanitary conditions of that era ultimately led to). And this was not accidental. In many cultures, the concept of physical purity is associated with health and beauty, although the existence of microorganisms was learned only in the 17th century, and the word Bacterium appeared in the 19th century. It seems that people intuitively understood that a person needs to maintain cleanliness, just did not know what mechanism is behind this.

    Today we know that we need to wash our hands before eating in order to get rid of pathogenic organisms and reduce the likelihood of diseases. We take a shower, brush our teeth, wash dishes, floors - all this in order to avoid the harmful effects of bacteria, whether it is an unpleasant odor or the development of infection.

    But not so long ago, it became clear that excessive purity also harms: the immune system weakens if it is less likely to encounter different types of bacteria, and hot water destroys the protective fat layer of the skin and its microbiomes, which is why it copes worse with its functions. Scientists have concluded that bacteria are an important part of our lives. They support the functions of our organs, but at the same time they can do much harm.

    Now there is enough research to evaluate how intestinal microbiota is associated with type 2 diabetes, atherosclerosis, obesity, ulcerative colitis and Crohn's disease. We will talk about them now.


    Obesity is a condition in which the amount of adipose tissue in the human body exceeds the norm. Estimate the amount of excess weight on a person’s body mass index. Sign of excess weight is index 25, and obesity - 30. You can check your BMI using a calculator . BMI is not for everyone. For example, with a muscular physique, he will also be tall, therefore, in order to assess the full picture, they can additionally measure the waist.

    Obesity can lead to metabolic syndrome, atherosclerosis, type 2 diabetes, high blood pressure, some types of cancer and other dangerous diseases and conditions. The main reason for weight gain is the consumption of calories, which are not consumed by the body, but are stored in the form of adipose tissue.

    Microbiota is involved in the metabolism of substances. This was revealed from several observations. Firstly, the microbiota of thin people is different from obese people. Secondly, if you transplant the microbiota of a large mouse to another, which grew in a sterile environment without bacteria, the second will rapidly gain weight. Also, if the microbiota of a complete person is transplanted into a sterile mouse, it will also gain weight.

    There is evidence that a diet high in carbohydrates contributes to the development of this type of microbiome, in which the body receives more energy from food, which increases the risk of obesity and metabolic disorders. The bacteria of the Firmicutes department are probably helping us with this.

    They break down dietary fiber and produce more energy from food than others, which can increase the risk of obesity. But, as we wrote in a previous article, research yields mixed results. Sometimes people with obesity have a higher representation of another department, which is associated with the Western type of nutrition.

    In high-fat diets, bacterial cells are thought to break down and a large amount of lipopolysaccharides (the remains of dead bacteria) enter the bloodstream , leading to mild inflammation and an  increased risk of obesity .

    Studywith the participation of twins showed that a less diverse microbiome is associated with weight gain, and vice versa, a diverse bacterial composition reduces the likelihood of obesity. Moreover, diversity was positively correlated with fiber intake in the diet.

    There are also several bacteria that protect humans from obesity - Akkermansia muciniphila and Christensenella. About the first we wrote in a previous article , and the second is interesting because it is from all other genera most commonly transmitted by inheritance.

    Today, to combat obesity and overweight, a patient may be offered a microbiota transplant. Basically, this procedure is done in foreign clinics, since in Russia it is still being carried out in experimental mode.

    Type 2 diabetes

    Type 2 diabetes is a chronic disease in which the body cannot cope with incoming glucose. When glucose enters the bloodstream, the hormone insulin helps transfer it to the cells, and stores the rest in the form of glycogen. In type 2 diabetes mellitus, insulin resistance develops: the body ceases to respond to it and glucose does not reach the cells, but remains in the bloodstream.

    Excessive glucose in the blood can lead to damage to nerves, kidneys, eyes, high blood pressure, atherosclerosis, and other diseases of the heart and blood vessels. One of the main factors in the development of type 2 diabetes is obesity. Abdominal fat cells are thought to release pro-inflammatory substances that make the body less sensitive to insulin.

    According to research, the microbiota of people with type 2 diabetes contains a lower birth rate of the Firmicutes department. This department is just the main one for fiber processing and the production of butyric acid. Also in the microbiota of people with type 2 diabetes, more pathogenic and opportunistic microorganisms were found, such as Bacteroides caccae, Clostridium hathewayi, Clostridium ramosum, Clostridium symbiosum, Eggerthella lenta and Escherichia coli (Escherichia coli).

    Interestingly, not all types of fiber reduce the risk of type 2 diabetes. A meta-analysis of 9 large studies showed that the risk was 33% lower in those who adhered to a whole-grain diet. For those who consumed mainly vegetables and fruits, the risk did not change.

    Fruits and vegetables contain mostly water-soluble fiber, while cereals are insoluble. It is difficult to explain why insoluble fiber is the one that lowers the risk of diabetes. Perhaps this is due to the fact that vegetables and fruits contain much more simple sugars than cereals.

    There is another interesting suggestion. Several studies have shown a positive association between a protein diet and the risk of type 2 diabetes. Scientists have suggested that insoluble fiber can affect the absorption of protein in the body. And it seems so. A study in obese people measuring various biomarkers in feces and urine showed that animal protein is less absorbed in the small intestine when cereal fibers are added to the diet.


    Atherosclerosis is a condition in which deposits of cholesterol form in the vessels. These plaques interfere with the normal flow of blood to the brain and heart, which can lead to coronary heart disease and stroke.

    One of the main causes of atherosclerosis is the high levels of cholesterol and triglycerides in the blood, which leads to a diet rich in saturated fats. Microbiota can affect the levels of these substances, thereby increasing or decreasing the risk of developing atherosclerosis.

    The mechanisms, again, are unclear (you probably realized that the weakest point of research is to find a causal relationship), but there are some interesting suggestions. Some bacteria can synthesize bile acids, which are absorbed by the intestines and, through receptors, affect glucose and fat metabolism.

    Comparison of the microbiome of healthy people and people with atherosclerosis showed that the former have a higher representation of the bacteria Roseburia and Eubacterium (for more information on bacteria, see the previous article ), and the representation of Collinsella is lower. Also, according to studies, the bacterium Akkermansia muciniphila improves the barrier function of the intestine and affects the protection against atherosclerosis.

    Another study notes that people with atherosclerosis have a higher prevalence of pathogenic bacteria such as Escherichia coli, Klebsiella spp and Enterobacter aerogenes. Ruminococcus gnavus, a bacterium that is associated with intestinal inflammation and a low diversity of microbiota, was also higher among a group of people with atherosclerosis. It is noted that the microbiota of people with atherosclerosis is less balanced and diverse in comparison with a healthy group.

    Inflammatory bowel disease

    Inflammatory bowel disease (IBD) is a chronic inflammation of the gastrointestinal tract, which includes Crohn's disease and ulcerative colitis. With these diseases, cells of the immune system attack healthy intestinal tissues, which leads to inflammation, bleeding and ulceration. Irritable bowel syndrome does not belong to this group of diseases.

    The main difference between the diseases is that ulcerative colitis develops only in the intestine, while Crohn's disease can occur in any organ of the gastrointestinal tract. Inflammatory bowel disease can lead to other dangerous conditions, such as colon cancer.

    Intestinal bacteria produce metabolites that are involved in immune responses and the formation of the environment. For example, butyric acid can regulate the immune cells of T-killers and trigger the antibacterial functions of macrophages, which protects against the formation of ulcers. According to studies , fecal samples of patients with IBD contained less butyric acid, and microbiota - less bacteria that produce it.

    Scientists also note that in people with IBD, the presence of bacteria Roseburia hominis, Dorea formicigenerans and Ruminococcus obeum is less, and in general their microbiota is less diverse in comparison with a healthy population. In the intestines of people with IBD, there is an excess of bile acids that are involved in the body's immune response. However, a less diverse microbiota cannot produce a sufficient amount of many other important metabolites. This may be one of the reasons why immunity cells begin to destroy healthy body tissues.

    For the treatment of ulcerative colitis and Crohn's disease, probiotic bacteria can be used that maintain the balance of microbiota, strengthen the protective functions of the mucous layer and slow down the death of intestinal cells. Also, the use of microbiota transplantation for the treatment of inflammatory bowel diseases is being actively studied.

    In the next article, we will describe in more detail how to take care of bacteria: how to feed them, what to protect from and why to play sports.

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