No, you don’t have two kilograms of bacteria in your body, and an imbalance of bacteria doesn’t cause most diseases

The study of the bacteria that live in our gut, the so-called microbiome, is one of the leading research fields that has become fashionable. So much so that some exaggerations and lies have infiltrated strictly scientific information, possibly to the detriment of future research on the matter. That’s the view defended by two British researchers, Alan Walker and Lesley Hoyles, who published an article in the journal Nature Microbiology on Monday, titled Examples illustrating common myths or misconceptions in the human microbiome literature.

Bacteria are becoming more resistant


“While certainly exciting, the growing focus on microbiome research has unfortunately also created hype and entrenched certain misconceptions,” they wrote. “As a result, many unsupported or undersupported claims, based on become ‘facts’ over and over again.”

They note that some hoaxes about bacteria are more common than others, and some are relatively trivial, but collectively they highlight just how pervasive misinformation surrounding the human microbiome is. And, “given the potential importance of the human microbiome to health, these claims must be based on evidence,” they emphasize.

Here are some major misconceptions about the microbiome:

Our bacteria weigh no more than 1 to 2 kg

This kind of inaccurate information even appears in some scientific studies, although its sources are often not cited. “The majority of the human microbiota is found in the colon, and these microbes typically make up less than half the weight of fecal solids,” the authors note. “It is more likely that the total weight of the human microbiota is less than 500 grams, and in some cases may even be greater than that.” Much smaller.”

There are not ten types of bacteria in every human cell.

This myth was buried in 2016 when a paper by Sender, Fuchs and Milo in PLOS Biology recalculated and found the source of the overestimation in a paper from the 1970s. “A more detailed analysis suggests that while the true figure is still impressive, it may be closer to a 1:1 ratio,” said the paper’s authors. “It should be noted that this ratio may vary from person to person, depending on factors such as the size of the host and the amount of fecal material in the colon.”

Altered microbiomes don’t explain obesity

Based on a series of rodent studies and single or narrow human studies, it has been claimed that there is a link between the population of bacteria that live in our guts and obesity. “However, as with many other studies reporting associations between specific microbiota signatures and disease, reproducibility was poor,” the article’s authors note. “Indeed, at least three meta-analyses now report that this finding is inconsistent across human studies, and that, in fact, no reproducible taxonomic signature exists for human obesity.”

The elusive concept of ‘dysbiosis’

It is increasingly common to read about so-called deleterious interactions between microbiomes and their hosts that lead to different diseases, but in a large proportion it is simply not clear whether this is the case. “Unfortunately, the term is an oversimplification and inherently flawed,” the article states. “Microorganisms and their metabolites are neither ‘good’ nor ‘bad,’ they just exist.” They also emphasize, “Ecological The term “dissonance” is increasingly used, “which is a vague term with limited clinical applicability”. “This is likely to contribute to disease progression in some conditions, including inflammatory bowel disease,” they acknowledge. However, such alterations are rarely consistent, and microbiomes are present across individuals in both healthy and disease states Huge difference. This makes it extremely difficult to identify gut microbiota patterns with the specificity and reproducibility required for clinical practice.

“Attempts to define the ‘tipping point’ at which changes in microbiome composition definitively affect disease progression have so far failed to achieve a clear consensus due to lack of consistency across studies.” Thus, they conclude, this is a problem that has not yet been established. A leap forward in evidence that signature microbiomes play a role in ‘most’ diseases.

it is not inherited from the mother

“The microbiome is inherited from the mother at birth” is another widespread misinformation, say Walker and Hoyles, which they see as a good example of the nuances that go into describing the human microbiome. how important it is. “While some microbes are transferred directly from mother to infant at birth, there are very few species of microbiota that are truly ‘heritable’ and persist in offspring from birth to adulthood,” they note. Remember, every adult We all end up with unique microbiome profiles, even identical twins raised in the same family. Thus, factors such as environment, diet, antibiotic use, and genetics play a much larger role than so-called direct “inheritance” from the mother, which plays a minor role.

It’s not a new science

Although the media continues to present this science as something new, the truth is that it has a very long history. “The pace of human microbiome research has accelerated enormously over the past 15 years, but the field is not in its infancy,” Walker and Hoyles note. “In fact, the study of human-associated microbes has a rich history since at least the late 19th century.” Escherichia coli was first isolated in 1885, Bifidobacteria were described in 1899, and Metchnikoff speculated on the importance of beneficial gut microbes in the early 20th century. As often read in many sources, Joshua Lederberg coined the term “microbiome” in 2011, which is also untrue, as it has been used in the field for at least a decade.

against dogma and simplification

country roseA researcher at the Ramón y Cajal Hospital and a member of the Specialized Group for Research on the Human Microbiome (SEIMC-GEMBIOTA) believes that the publication of this article could not be more timely. She knows this firsthand, as she is one of those professionals who often faces the misconception of “dysbiosis”. “Although the ‘normal’ composition of the microbiome has not been determined, it is the first thing patients learn,” he explained to 20 years and there isn’t even a standardized procedure. In fact, it hasn’t been brought into public health because deciphering the ingredient doesn’t have any direct translation for the patient.

There is no good or bad bacteria/microbiome, it all depends on the environment and location

The researcher recalls that mouse model research is crucial to science, but agrees that it often distorts reality compared to humans. “I am left with the conclusion that there is no good or bad bacteria/microbiome, it all depends on the environment and location (e.g. we all have Escherichia coli in the gut, but can cause infection when it reaches the urinary tract).

Toni Gabaldón, Head of the Comparative Genomics Group at the Barcelona Biomedical Research Institute (IRB Barcelona) and the Barcelona Supercomputing Center (BSC-CNS), believes that people working in this field have these clear ideas, which For those working in other fields or the general public, leads to confusion. In a statement to Science Media, he reassured: “The field of microbiome research (like other rapidly evolving fields) was influenced by the existence of early dogma and simplifications based on very limited information assumptions, and we must learn more as we learn more. Make corrections and adjustments.” Center (SMC).

We are in the golden age of the microbiome, we are in the stone age. But make no mistake, our microbes have a huge impact on health.

Rob Knight, director of the Center for Microbiome Innovation and a professor at the University of California, San Diego, agrees that most of these mistakes and misconceptions are well known to experts in the field, but “it’s helpful to summarize them as an approach.” “Local, first of all because a lot of people are joining the countryside at the moment,” he told SMC. In his view, the non-reproducibility of microbiome-disease associations is an important issue, but it’s more nuanced than described in the article. He noted: ” To be used as a clinical test, microbes or microbiome patterns do not have to cause disease, but only need to serve as accurate markers of disease. ”

Ignacio López-Goni, a professor of microbiology at the University of Navarra, also believes that the claims in the article are generally accurate. “But it should be remembered that there is more that we don’t know than we do,” he said. “We’re not actually in the golden age of the microbiome, we’re in the Stone Age.” He assures that despite the limitations, there is no doubt that the study of the microbiome today opens up new possibilities for personalized medicine. “We don’t know much about the mechanisms,” he concludes, “but there is no doubt that our microbes have a huge impact on health.”

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