Instead of being passive passengers of the human body, bacteria in the gut affect the health of the digestive tract, increase and decrease appetite, and change taste preferences. They can help you lose weight, or they can add pounds. They can make you sad, or, on the contrary, they can add stress resistance. We talk about how it works in our article.
- What is the gut microbiome
- How microbes take care of gut health
- Microbes, metabolism, and appetite
- “Fattening” bacteria
- Germs and stress
- bacterium medicine
What is the Gut Microbiome
The gut microbiome is the collection of microorganisms — bacteria, archaea, eukaryotes, and viruses — that live in the gastrointestinal tract. The intestines contain the largest population of microorganisms in the human body.
Gut microbes perform many functions:
- protect against harmful microorganisms and teach the immune system to distinguish “friends” from “enemies”;
- help digest certain substances, such as dietary fiber;
- produce important and useful molecules, in particular, butyric acid;
- promote the absorption of minerals (magnesium, calcium, and iron).
Considering how many important functions the gut microbiome performs, scientists are currently treating it as a separate organ.
These microbes regulate the work of other organs, that is, conditionally becoming part of the endocrine system.
How Microbes Take Care of Gut Health
Microbes primarily take care of their home, that is, the intestines. For example, they help the intestines to receive enough blood with oxygen and nutrients. Intestinal microbes activate the so-called Paneth cells in the intestinal wall, which secrete peptides responsible for increasing the number and branching of blood vessels. This means that the microbiome indirectly ensures normal blood supply to the intestines. Paneth cells are specialized secretory epithelial cells located in the small intestinal crypts of Lieberkühn. The dense granules produced by Paneth cells contain an abundance of antimicrobial peptides and immunomodulating proteins that function to regulate the composition of the intestinal flora.
In addition, microbes interfere with the development of inflammation by affecting the intestinal lining.
The intestinal lining is a natural barrier that prevents pathogens and toxic substances from entering the body which can lead to inflammation.
The intestinal lining consists of:
- A layer of epithelial cells connected by tight junction proteins.
The mucus contains immunoglobulin and antimicrobial peptides. If a harmful bacterium gets into the “mucus trap”, it has a hard time. Mucus is constantly produced in the goblet cells located in the intestinal wall. The microbiome is able to influence the goblet cells so that they secrete more mucus.
The second component of the intestinal barrier is the intestinal epithelium, whose cells bind tight junction proteins. There are data showing that the composition of the microbiome is associated with more or less tight contacts between epithelial cells, that is, with its greater or lesser permeability. However, the mechanisms of influence of the intestinal biota on tight junction proteins are still unknown.
Protection against inflammation is provided by a microbiome with a normal composition. However, if the composition of the microbiome is disturbed, for example, if the number of pathogenic bacteria increases, the intestinal epithelium becomes more permeable. This leads to the fact that parts of the bacteria enter the bloodstream and provoke inflammation themselves.
Microbes, Metabolism, and Appetite
The human gastrointestinal tract produces many hormones. For example, the stomach secretes the hormone ghrelin, which is associated with an increase in appetite: its concentration is highest before eating, and lower after.
The large intestine secretes peptide YY and glucagon-like peptide-1 (GLP-1). Peptide YY slows down the secretion of digestive enzymes, reduces the motor activity of the digestive tract, and reduces appetite. GLP-1 stimulates the release of insulin.
Fat cells secrete leptin, a satiety hormone that reduces energy consumption. The hormones of the gastrointestinal tract, interacting with each other, ensure normal energy consumption and metabolism.
According to recent data, an important part of the digestive hormonal “orchestra” is the microbial population of the intestine.
So, in the process of digesting carbohydrates, bacteria secrete short-chain fatty acids that affect appetite and metabolism.
Another example is the prebiotic inulin, a substance found in fruits and vegetables that promotes the growth of beneficial bacteria in the gut. Its use affects the microbiome, as well as all hormones at once: ghrelin, leptin, peptide YY and GLP-1. Intestinal bacteria can also influence the expression of receptors in the intestinal wall that are responsible for the perception of certain ingredients. Gut biota also affects appetite.
So the bacteria from the bowels of the intestine, in a sense, orchestrate at what point we want something tasty and in what quantities!!!
Given the influence of the microbiome on metabolism and appetite, it is not surprising that its composition can affect the maintenance of healthy body weight.
The probiotic Lactobacillus rhamnosus PL60 reduces the growth of body weight and adipose tissue without affecting food intake.
In experiments, the weight of mice depends on the fungi that inhabit their intestines. Rodents that have more Thermomyces fungi (which are used to break down fats) and fewer Saccharomycetes, i.e. yeasts, gain about 15% more weight than mice with a different gut microbiome composition.
Scientists have also conducted a number of experiments with the transplantation of the intestinal microbiome.
It turned out that sterile mice, devoid of bacteria in the intestines, weigh less than their “normal” counterparts, and do not get fat even on a diet high in fat and sugar. If their intestines are colonized with a microbiome from a fat mouse (or an overweight person), they gain weight faster than rodents that have been transplanted with the microbiome of a normal mouse.
Conversely, if animals are transplanted with microbiome from underweight rodents (due to gastric bypass), they will begin to lose weight.
Germs and Stress
Through as yet unknown mechanisms, the gut microbiome regulates psychological state. Some indirect evidence suggests that, through effects on the vagus nerve and the release of certain neurotransmitters (eg, serotonin), the gut microbiome may play a role in the stress response and depression.
Animals raised in a germ-free environment show an increased response to psychological stress that normalizes after colonization with certain bacterial species, including Bifidobacterium infantis.
One day, microbiome from depressed patients were transplanted into sterile rats. It turned out that in patients with depression, the gut microbial population is less diverse than in healthy people, and its transfer to rats leads to the development of anxious behavior and causes anhedonia, that is, a decrease in motivation and an inability to experience pleasure.
In a randomized controlled trial, probiotic supplements improved sleep and reduced stress and cortisol levels in Japanese medical students. In another study, for a month of consumption of a fermented milk product containing probiotics, in healthy women, the activity of “emotion centers” in the brain decreased when exposed to emotionally colored stimuli (a task for attention and recognition of emotions; emotional faces attention task).
It seems tempting to suggest that effects on the gut microbiome might be beneficial in the treatment of metabolic and stress-related diseases. However, data on the use of prebiotics and probiotics as medicines are still scarce.
Taking a probiotic containing Lactobacillus reuteri for 4 weeks was associated with an increase in the secretion of glucagon-like peptide-1 by 76% and insulin by 49% compared with the control group. Therefore, in theory, a tablet with the bacterium could improve insulin release in diabetic patients. There are also preliminary data on the effect of the so-called “psychobiotics”.
Psychobiotics are bacteria that, when taken orally in sufficient amounts, benefit the health of patients suffering from mental illness.
These bacteria are capable of producing and delivering neuroactive substances such as gamma-aminobutyric acid and serotonin. Preclinical studies in rodents indicate that certain psychobiotics have antidepressant or anti-anxiety activity. But while “bacterial” therapy can have a positive effect on depression, anxiety, and stress, some studies do not reveal this effect.
We’ll have to wait for more data before doctors start routinely prescribing bacteria-drugs.
This does not constitute medical advice, always seek the direct advice of your Doctor or Medical Provider for your specific health care or needs.
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