Can You Really Control Your Mental Health From Your Gut?

For all of the “hot girls have IBS” jokes we make, an upset gut isn’t actually something all that desirable. Whether you’re someone who deals with the occasional rough bout of digestion issues or a more chronic condition, you’ll know that these unwanted physical symptoms take a toll on your mood. And if symptoms of an unhappy gut drag on, your mental health can be affected, too. 

The human gut is an incredible system which mostly squelches away, filtering out what we do and don’t need, without us realising. Adults have around nine metres of bowel in total: the small intestine, a long, narrow tube of about seven metres and the large intestine, so called because of its wide diameter. The latter is about one and a half metres long. That is a lot of piping. Naturally, things can go wrong sometimes. Symptoms like diarrhoea or constipation, bloating, wind, pain and nausea tend to alert us to our gut not functioning well. An upset gut can also go hand in hand with an upset mind; a person not functioning well.

In the not-too-distant past, the idea that Hollywood actors would be encouraging us to keep our microbiome healthy by selling us probiotics would have seemed ridiculous. So, too, might rappers endorsing "gut health" vitamin supplements. But "gut health" has become a byword for "wellness".

The wellness industry has been pivoting to the word "bowel" for some time and much currency (literally) is now attached to words like "probiotic" and "microbiome". Being more in touch with our bodies and how what we feed them can affect the way we feel is broadly a good thing, particularly when the stigma surrounding guts and poo has, for so long, stopped many people addressing health issues. But what do these terms actually mean and how much "science" is being extrapolated for profit?

The link between emotional distress and difficult sensations is long established. When we’re highly stressed, our primitive fight-or-flight response is activated, flooding the body with stress hormones which can cause all manner of physical symptoms. Chronic stress can leave the body in a "high alert" state, meaning we’re in fight-or-flight mode all the time. Again, the physical effects can be significant and sometimes the body tells us we’re emotionally distressed before we can connect thought to feeling. Often, the gut is shouting loudest.

A troubled bowel can send signals to the brain and a troubled brain can send signals to the bowel. This two-way communication highway is known as the brain-gut axis. Over the last decade, it has become increasingly clear that the connection between the brainstem and the gut, which are linked by the vagus nerve, plays a central role in our emotional states.

We know that the gut provides approximately 95% of the feel-good hormone, serotonin, in the body and that imbalances in gut flora have been linked to irritable bowel syndrome (IBS), immunity disorders, Alzheimer’s, arthritis, obesity and, more generally, a person’s energy levels. It is clear that more targeted research into the brain-gut axis could lead to far more sophisticated treatment options for many health issues — including all kinds of mental distress — but the view is still misty: We know a lot, but far from everything.

Then comes bacteria, which human beings are absolutely teeming with. Each gut contains about 100 trillion microorganisms like microbes, viruses and fungi that, together, are known as the human microbiota. "Microbiome" stands for all the genes contained in the microbiota and is as unique to an individual as a fingerprint. Microbiota have so many important functions within the body that they’re increasingly being referred to as "the second brain". Along with assisting with digestion and absorbing nutrients we take in, our microbiota release chemical profiles that regulate our immune function, metabolism and, most interestingly to me, mood.

As someone who has, putting it politely, felt stress in the gut for all their adult years, I’ve long been tuned into this area of research. I cannot claim any kind of authority, but in the years I have spent interviewing research scientists, doctors, psychiatrists and psychologists, the message has always been the same: Microbiota are clearly involved in our overall state of health, but we haven’t unlocked all the answers yet.

We have good reason to believe that microbiota play a role in our emotional state and social behaviours, and could be linked to problems like depression, but the theories are largely based on studies done on mice. There are few human studies that support the links. That being said, this doesn’t stop entire industries and commercial companies capitalising on these kernels of theories, and our curiosity, for profit. Where there are tentative links, there is money to be made.

Microbiota tests are increasingly being offered by functional medical practitioners with a view to improving skin, sleep, digestion, mood and more, but are also available to do at home with companies, such as Atlas Biomed. When I was researching my book Hormonal, I went to see a Harley Street nutritionist after he said he could test my microbiota and potentially establish a link between my gut health and PMS. After I’d reeled off my list of symptoms — anxiety, tears, pain, constipation and bloating — his working diagnosis was dysbiosis (unhealthy microbiome and excess yeasts).

To confirm this, I did a urine test (£279), which was sent to a lab called Genova Diagnostics. When I went back for my results, the nutritionist described an "overgrowth of lactic acid-producing bacteria and excess yeasts", which were associated with distorted signalling to the brain. Naturally, I would need a stool test (£355) to confirm. I also had a "slightly elevated" level of an inflammatory marker called picolinate, which was "associated with mild brain inflammation" that could be causing "mood disturbance". This could be "corrected" with more oily fish. He suggested kippers for breakfast.

Brain inflammation. This stayed with me for some time, although subsequent conversations with neuroscientists assured me that the term meant nothing in this context — not least from a urine sample. I also learned that the Genova Diagnostics lab (used by thousands of functional medicine practitioners across the UK and Ireland) has been repeatedly sanctioned for its pseudo-scientific workings. Until I found this out, the theory was briefly compelling. But no test is ever a complete diagnostic tool. If someone has gut-related symptoms, it is a given that their microbiota is skewed — one stool sample, on one day, is a snapshot, not the full picture.

In the wake of the wellness industry boom, having endless testing has become a proxy for self-care — particularly where the gut is concerned. But not only do many of these tests have a very poor scientific basis, endless cycles of testing often reinforces the idea that there is something terrible lurking somewhere. For most people, this will not be the case. It is currently impossible to make crystal clear, measurable connections between the gut and mental health on an individual level. However, even if I, a quite anxious person, could possibly connect some iffy microbes with a spell of panic attacks, the solution would be the same as if the microbes hadn't been measured. I’d have to address the basics: diet, sleep, exercise and stress levels.

We don’t need to know what exactly is going on in our gut at all times. We do know that the modern diet is often loaded with carbohydrates and processed grains, which feed the unhelpful bacteria in the gut. Moderating our intake of these, eating more vegetables than anything else and incorporating some probiotic and omega-3-rich foods (oily fish) into our diet has long been recommended as the healthiest approach. (The Mediterranean diet has been shown to increase the diversity of bacteria in the gut.) Habits that are bad news for the heart, lungs and brain — smoking and drinking, for example — could also negatively affect the microbiome.

As for the lucrative world of probiotic supplements, the science is still out on their benefits. Many commercial pills and capsules claim to "boost gut health" and introduce "good" bacteria, but because the supplement industry is so poorly regulated, there is no guarantee that what’s on the label matches what’s inside. Studies have been inconclusive about whether probiotic supplements will actually improve everyone’s gut health, too — the evidence is much stronger for people with antibiotic-related diarrhoea or inflammatory bowel diseases like Crohn’s or ulcerative colitis. Instead of expensive pills, beneficial bacteria can be absorbed from fermented foods like yoghurt, kefir, sauerkraut, kimchi and miso. (I can personally attest to increased gut peace after introducing these things.)

At some point in the future, perhaps regulating gut bacteria could become a way of treating anxiety. But, again, we know enough to make basic changes for our overall health already. Our current understanding of the mighty gut-brain axis only strengthens the growing evidence that a healthy, balanced diet is integral to both our physical and mental health — as if the two can possibly be separated.