A recent study performed by scientists from the Weizmann Institute of Science in Israel was conducted to determine the effects of probiotics on the human gut. Unlike other studies, which measure the bacterial content of fecal samples to approximate the composition of bacteria living in the gut, this study used endoscopies and colonoscopies to directly measure the gut microbiome of participants.
One portion of the study looked at the results of a probiotic taken by participants with typical gut microbiomes. Many participants who consumed the probiotic were unaffected by it, with the probiotic microbes simply passing through the digestive system and being eliminated as waste. The guts of a few other participants were found to have accepted growth of the probiotic bacteria for a short period of time, but a study of fecal samples from the participants did not accurately reflect the state of their gut colonies.
Another portion of the study focused on the effects of probiotics on microbial colonization of guts devoid of microbes. After dosing participants with a course of antibiotics to clear the gut of existing microbes, the volunteers were given a placebo, a probiotic, or a fecal matter transplant (FMT) from a personal sample taken from each participant prior to the antibiotic treatment. The results from the probiotic portion of the study were less than positive; participants who consumed the probiotic were not able to restore their previous microbiomes. Their guts were colonized by the probiotic microbes which persisted rather than allowing the past microbiome to re-emerge after seeding growth.
What Are Probiotics?
Probiotics are mixed or monocultures of living microbial species that are consumed in an effort to affect the health of the gut by manipulating or modifying the microbiome. These days, probiotics come in the forms of many different types of food, such as kimchi and miso paste, drinks, such as kombucha tea or kefir, or encapsulated supplements, but one of the early and most recognized forms of probiotic is yogurt. Probiotics have become large trend with minimal science backing up their efficacy thus far. One of the more recent fads of probiotics has been “raw water“, expensive and completely untreated water that may contain beneficial probiotics.
What is the Gut Microbiome?
The gut microbiome is the community of microorganisms that live in the gut of organisms. The microorganisms that have colonized the guts live in a mutually beneficial relationship with the host organism. In the human body, 57% of the cells are actually microbes; over half of the cells found in our bodies do not actually belong to us.
- Microbiome definition: all of the microorganisms living in a specific ecosystem; in the case of the gut microbiome, the ecosystem is the intestines.
While many of the microorganisms of the gut microbiome are bacteria, other microbes such as virus particles, fungi, and archaea are also a part of the microbiome. Because the small intestine is closely attached to the stomach, and the conditions are poorer for microorganism growth, many of the microbes of the gut microbiome inhabit the large intestine.
It is fairly common knowledge that the main role of the microbes living in the gut is in food digestion. Microbes living in the gut are able to break down food that is indigestible by the host organism, and while the microbes extract energy from what they have processed, the host organism also benefits from the process. Research has shown that the gut microbiome has more of an impact on more systems that originally thought. Studies have linked the gut microbiome to obesity, allergies, and an ability to affect the brain and behavior of an organism.
What Are Probiotics Supposed To Do?
The theory behind consuming a probiotic is to re-establish or aid in the healthy balance of natural flora in the gut. Probiotics are meant to act on the gut flora in one of two ways: probiotic species can repopulate the gut if it has been disrupted, or probiotics can help to protect a gut that has been compromised.
Probiotics are often taken to repopulate the gut when the normal flora living in the gut have been affected by something like a course of antibiotics. While the antibiotics taken to treat a bacterial infection will have eliminated the pathogenic bacteria, the beneficial microbes living in the gut will also have been affected, and perhaps even completely removed. By taking a probiotic, the hope is that the living microbes in the probiotic mixture will be able to recolonize the gut, seeding it and allowing the previous inhabitants of the gut to re-emerge and once again thrive.
Probiotics can also be used in an attempt to re-establish a healthy state of microorganisms in the gut that have been compromised by a pathogenic species. The basic principle is that the probiotic microbes will be able to outcompete the pathogenic microbes in some fashion. There are four main tactics that can be employed by probiotics which have successfully colonized the gut to protect the gut from invading pathogens:
- By outcompeting for limited nutrients
- By colonizing all possible livable spaces within the digestive system and blocking out invaders
- By stimulating the immune system
- By directly attacking invaders by producing and releasing antimicrobial chemical agents
Using one of or some combination of these tactics, probiotics are meant to defend the gut against invading pathogenic bacterial species.
What Do Probiotics Actually Do?
As shown in the results of the study by the Weizmann Institute of Science in Israel, often probiotics don’t do anything at all. In many cases, probiotics that have been consumed are simply eliminated after passing through the digestive tract. When probiotics are able to effectively colonize the gut, they tend to actually prevent the natural states of native flora from re-establishing themselves. This can have an adverse effect on the health of the individual, as the probiotic mixture may not contain all of the microorganisms necessary to maintain gut health.
Science still has no real idea what a healthy gut microbiome contains. It is known that the gut microbiome of humans is highly varied between individuals, and is affected by numerous factors, including diet and general health state. It’s clear from the results of research so far that any attempts to modify or manipulate the gut microbiome will have to be based on an individual, tailored level, and not simply a universal probiotic treatment.