Your gut is a wild place. Home to estimated trillions of bacteria (1,2) and millions of neurons (3), this organ system is full of surprises. While most understand that they must treat their gut well and feed it fiber (4), there are many lesser-known gut facts out there - we’d like to share a few of our favorites.
Your birth affects your bacteria
You have a microbiome from the moment you’re born (5) (or potentially even earlier (6)), so it’s unsurprising that your gut is influenced by mom. Research suggests that babies born by C-section have different microbiome compositions than those who undergo vaginal birth (7,8). Why birth method would have this effect isn’t yet understood, but one reason could be that babies pick up bacteria during the “normal” journey out of mom (9). Another may be the delay in breast-feeding that often occurs after a C-section birth – breast-feeding is known to alter the gut microbes of newborns (10).
You have more than bacteria living in your gut
Did you know that your GI tract is home to fungi (11) (the spore-producing organism group that includes mold and mushrooms (12))? Multiple fungal species, such as yeast, are found in a healthy person’s GI tract. Research suggests that the internal fungi population changes dramatically over time, unlike the (relatively) stable microbiome (13,14). While not as consistent or as diverse as your microbiome, your “mycobiome” could still affect your well-being. Mycobiome changes are associated with irritable bowel disease (15) and neurological disorders such as multiple sclerosis (16), though if and how fungi directly influence these health problems remains a mystery.
Your gut is strongly shaped by your environment (and maybe not so much by genetics)
In order to determine what influences our gut microbiome composition, a recent study looked at both the microbiome and the genetics of over 1000 people (17). Surprisingly, the effect of genetics was small, while the effect of environment was much larger. In fact, unrelated people who lived together had more similar microbiomes than related family members who have never lived together (e.g., cousins). This could partly be due to housemates sharing meals - the best predictors of microbiome makeup in the study were related to diet, such as blood glucose levels and BMI.
Not all species have a microbiome
We (and many animals) have a beneficial relationship with gut bacteria (18). They get to live in our guts and have food delivered to their door, and in exchange they break down foods that our guts can’t. Yet, recent evidence suggests that a positive relationship with gut bacteria isn’t universal and may not even be the norm. Bats and birds have very different guts than us (19), as they lack some bacteria types found in the “typical” mammal microbiome. Other species seem unaffected by changes to their gut microbe composition (20) or have no beneficial gut bacteria altogether (21,22). Why certain species don’t use microbes for digestion is unclear - scientists think that it could be due to diet differences (21) or variation in gut structure (simple gut systems could make bad bacterial homes) (18). Understanding why may help us learn more about microbes’ effects on human health.
Your gut microbes can talk to your brain
Yes, your gut and your brain are linked (23)! Gut microbes can release neurotransmitters (24), the chemicals that neurons use to talk to each other, suggesting that gut microbes speak the same language. Eliminating or manipulating mouse microbiomes can lead to physical changes in neurons and broader changes in behavior (23). Mirroring these findings, humans with mood disorders such as depression (24) often have different microbial compositions than healthy individuals. Microbes also release many unique molecules that affect the rodent brain and are suspected to affect humans’ brains (25). So, your microbiome can, and likely does, talk to your brain - it’s quite the chatterbox!