How probiotics rebuild your healthy microbiota (bacteria) and improve your health

Impressive as it sounds, you have more microbes in your intestines than people living in our planet. There’s an estimate 100 billion bacteria living and reproducing inside, and you don’t even notice. According to the revisited measures of the human digestive tract, it has the surface area of 30 to 40 square meters, which can be compared to the surface of an apartment. This area is in constant movement and dynamic changes, and our digestive bacteria make up an important part.
The healthy bacteria in our gut prevents serious infections, modulate our immune system, influence the inflammation process, and even have an implication on our metabolism. As such, gut microbiota has become a target for prevention, and even therapeutic intervention, through probiotics, which are readily available without the need of a prescription. But what does the science have to say about probiotics and health?

Probiotics and their mechanism of action
The colonization of our gut by healthy bacteria depends on many different factors, and one of them is our diet. There are many products containing healthy bacteria for our gut, especially found in foods like yogurt, which undergoes a certain degree of fermentation. They contribute with different strains of bacteria. For instance, yogurt usually comes with Lactobacillus cultures, and fermented soy foods like tempeh usually contain Bacillus bacteria. All of them have different properties and mechanisms of action, some of them widespread in almost all probiotics, and others not so common:

Widespread mechanisms: Almost all bacterial strains in our gut cause a competitive exclusion of pathogens. This means that they colonize the mucosal linings of your gut and will compete with any bacteria that would cause disease. Almost all bacterial strains in probiotic foods and products regulate your intestinal transit and produce short-chain fatty acids from the remaining carbohydrates your body did not absorb by itself. Some of them can be absorbed, enhancing your uptake of nutrients, and others are useful for the metabolic functions in your intestinal wall.

Frequent mechanisms: These are common, but not widespread in all bacterial strains. Many probiotics are able to synthesize vitamins, metabolize your bile and serve as a reinforcement to your gut barrier, thus creating an additional protection against disease. There’s also research pointing out bacteria that neutralizes carcinogen molecules as well.

Infrequent mechanisms: Other mechanisms of action in probiotic strains are only seen in a few species. Some of them can be helpful for certain neurological problems, or modulate very specifically your endocrine system and immune response.

The main reasons why our healthy bacteria get affected is through antibiotic use, but our lifestyle, diet and stress can be also important modulators. Any disruption in gut microbiota could cause adverse effects, and the most commonly seen is diarrhea, especially in older adults. Increasing bacteria like bifidobacteria and lactobacilli usually improve these and other health issues, which is the reason why probiotics are often prescribed along with medications.

Effects on gut microbiota and gut metabolism
After a disruption in gut microbiota as a result of antibiotic treatment, diarrhea, and other conditions, probiotics can improve our gastrointestinal health by promoting healthy bacteria and making them compete with harmful microorganisms. Many of the bacteria selected for probiotic products synthesize bacteriocins, which are molecules with antimicrobial properties. These bacteriocins fight the invasion of disease-causing microbes they consider competitive strains, and may even modulate our immune system to improve our gastrointestinal defenses.

Thus, probiotics are not only new healthy bacteria for our gut. The strains are specially selected to counter the effects of pathogens to create a competitive exclusion through bacteriocins and other molecules. These mechanisms allow the resilience of our declining gut microbiota when we are undergoing antibiotic therapy or are facing gastrointestinal problems.

Probiotics have a positive effect on gut metabolism as well. As mentioned previously, they create short-chain fatty acids, named butyrate, propionate, lactate and acetate. In other cases, probiotic strains do not produce them but promote the growth of species that produce short-chain fatty acids. They are active metabolites capable of controlling local and systemic inflammation, lowering the pH in the gut, and even serving as signals to regulate satiety and promote the healthy growth of new intestinal cells. The same molecules synthesized by probiotic strains also regulate the intestinal transit by modulating the release of a hormone called glucagon-like peptide-1. So, next time you hear probiotics produce fatty acids don’t be scared thinking they are harmful. These short-chain fatty acids bring many benefits to the internal metabolism in your intestines.

Additionally, probiotics can influence the production of certain enzymes with impressive health effects. For example, the enzyme bile salt hydrolase is produced by many commensal bacteria and probiotic strains. This enzyme works on bile salts and forces your body to excrete an extra amount of cholesterol that was excreted along with bile and would otherwise be absorbed back into your bloodstream. The result is a probiotic strain with cholesterol-lowering effects. Another enzyme worthy of mention is the beta-galactosidase. This enzyme is useful in patients with lactose intolerance, and may improve most of their gastrointestinal symptoms.

These effects are only related to gut metabolism and gut microbiota, but probiotics have much more to offer. They modulate the immune system, can have an effect on the gut barrier and gut permeability, and communicates to the brain through a two-way communication system called gut-brain axis. There have been studies on many gastrointestinal conditions such as inflammatory bowel disease, irritable bowel syndrome, constipation, diarrhea, and even infantile colic. There’s no doubt we are only grasping the extent of probiotics, only starting to understand how bacteria can actually be our medicine.

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