How to Talk About the Gut Microbiome Without Falling Into Common Traps

One of the hottest topics we get asked about is the microbiome. It’s one of those areas that everyone seems to have an opinion on, but few people really understand.

With thousands of research papers published a year, it’s a complex and nuanced field, with more myths than a JRR Tolkien trilogy. And it’s these misconceptions that can cloud our judgment. That’s why I was so pleased to come across this paper that was published just two months ago. It’s a great overview of the current state of the science and the common pitfalls that we should avoid when talking about the microbiome.

As I read this paper, I sheepishly admit I’ve fallen for some of the myths. For instance, I’ve been known to say that the 'microbiome research is still in its infancy'. But that’s not true. The authors point out that the study of human-associated microorganisms dates back to the late 19th century, and that we have learned a lot since then. I guess what I really meant was that the microbiome is a dynamic and evolving field, where new discoveries are constantly being made and new questions are being raised. Rather than implying that we don’t know much about it, the reality is the more we discover the more questions raised. At the same time, many undersupported statements in this field have become 'fact' simply by being repeated over and over, like the one above.

Here are some more examples of persistent microbiome myths that lack a strong scientific basis.

Myth #1: Our microbiota weighs 1 to 2 kg.

Reality: This was one of the myths that I was hoping to be true That would mean that we could blame some of our extra weight on our friendly bacteria. But sadly, that’s not the case. The reality is that our microbiome weighs much less than that, around 500 g for most people.  

Myth #2: Microbiota outnumber our own cells 10-fold.

Reality: You may have heard that we have ten times more bacteria than human cells, which sounds pretty impressive. But is that really true? Well, it turns out that this number is based on a very rough and outdated estimatefrom the 1970s. More recent studies have shown that the actual ratio of microbiota to human cells is much closer to 1:1, and it can vary a lot depending on how much you weigh, how tall you are, and how much poop you have in your colon. Most of the studies that have measured the microbiome have focused on adults living in urbanised high-income countries, which may not represent the diversity and variability of the human population. We need more research on how the microbiome differs across different regions, cultures, lifestyles, and stages of life, such as infancy, childhood, adolescence, pregnancy, and aging. These factors may affect the composition, function, and impact of the microbiome on our health and well-being. 

Myth #3: Your microbiota was inherited from your mum at birth.

Reality: One of the fascinating things about our microbiota is how it develops and changes over time. You may think that we inherit our microbiota from our mothers at birth, but that’s only part of the story. The truth is that most of our gut microbiota is shaped after birth. 

It’s true that the mode of delivery, whether vaginal or caesarean, influences the initial colonisation of the baby’s gut by microorganisms. But this is not the only source of microbes for the baby. The baby also gets microbes from the environment, such as the air, the water, and the people around them. And these microbes are not static, but dynamic and adaptable. They can change in response to the baby’s diet, immune system, and health status.

One of the major events that affects the microbiome is complementary feeding, defined as the introduction of solid foods. This introduces a whole new range of nutrients and substrates for the microbes to feed on and compete for. As a result, the diversity and composition of the microbiome increases significantly after the introduction of sollids, and continues to change throughout childhood and adolescence.

But what about genetics? Studies have shown that identical twins raised in the same household have different microbiota configurations, which suggests that environmental factors play a bigger role than genetic factors in shaping the microbiota. Some of these factors include diet, antibiotics, stress, hygiene, and exposure to other animals and humans.

Myth #4: Most diseases are caused by a ‘pathobiome’

Reality: Given the amount of press the microbiome has received in recent years you would be forgiven for thinking that the microbiome is involved in everything from mood disorders to climate change. You may have also heard terms like pathobiome and dysbiosis, which imply that there is a normal or healthy microbiome and an abnormal or unhealthy microbiota. But is that really the case? 

The authors of this paper argue that there is no clear or consistent definition of what constitutes a pathobiome, which is supposed to be a microbiome that causes or contributes to disease. They point out that many studies that claim to find associations between the microbiome and various conditions do not take into account other factors that may influence both the microbiome and the disease outcome, such as age, BMI, sex, medication, and diet. Also, correlation does not mean causation, and it’s not easy to establish a causal link between the microbiome and health or disease.

Myth: Firmicutes make you fat.

Reality: You may have heard that some bacteria in your gut can make you gain weight, and that you should try to get rid of them or replace them with other bacteria. Specifically, you may have heard that Firmicutes are the bad guys and Bacteroidetes are the good guys when it comes to your body weight. But before you book your faecal transplant, let’s see if this is really true.

The evidence for this seems weak and inconsistent. The authors explain that this myth is based on studies that used rodents or human trials with small samples, and that did not account for other factors such as diet, genetics, medication, and inflammation. They also point out that these studies have produced inconsistent findings. In fact, three meta-analyses have concluded that there is no clear or consistent association between the microbiota and obesity.

Summary

These are just some of the highlights from this paper. We highly recommend reading it if you want to learn more about microbiota and how to interpret the research in this field. It’s a fascinating and important topic, but also one that requires caution and critical thinking. Don’t believe everything you hear or read about the microbiome. Instead, look for the evidence, the context, and the limitations of each study. And remember, there’s always more to learn.