When we’re feeling down, many of us comfort eat, responding to negative feelings with calorie-dense junk food such as hamburgers, french fries and chocolate. Sometimes treating yourself to a tasty – if somewhat unhealthy – meal is exactly what you need to chase away the blues, but often this pattern of behaviour is more about self-harm than self-indulgence.
The fact that our mental wellbeing influences our eating patterns is so well established that it is reflected in the commonly accepted criteria for recognising and treating depression. The American Psychiatric Association’s Diagnostic Manual notes that people tend to experience “significant weight loss when not dieting or weight gain … or decrease or increase in appetite nearly every day” when going through a period of depression.
Now, however, evidence is mounting of a bi-directional relationship between our moods and micro-organisms in the gut. Apparently, instead of us eating – or not – in response to certain emotions, our gut could sometimes be at the root of those feelings. This emerging idea is based on the fact that our gastrointestinal tract is home to trillions of microbes, collectively known as the microbiome.
A review article published earlier this year in the academic journal Hormones and Behavior suggests that the microbiome communicates directly with the brain, possibly via neural pathways. This is a two-way conversation, which scientists now refer to as the "gut-brain axis" or the "gut-brain connection". This relatively recent theory gives new meaning to the old sayings about trusting your gut and acting on gut instinct.
The exact “how” of the gut-brain-connection and all of its implications are still being slowly unravelled. In fact, the idea exists at the frontier of a pioneering interdisciplinary area of research involving psychology, microbiology and neurobiology.
The most obvious evidence for the gut-brain linkage relates to our experience of anxiety. Many of us feel butterflies in our tummies when we are nervous. In the case of chronic stress and anxiety, we might experience more severe gastrointestinal upsets and stomach aches. More seriously, peptic ulcers are frequently associated with generalised anxiety disorder.
From this evidence, it is clear that the worries in our heads can take a toll on our digestive system. But can the health of our stomachs also give rise to mental health problems? This idea has recently been explored in the context of irritable bowel syndrome (IBS), a common gastrointestinal complaint.
A study, published in 2015 in the interdisciplinary journal PLOS One, looked at the medical records of 4,689 Taiwanese IBS patients, spanning six years from their initial diagnosis. None of the patients had previously been diagnosed with any psychiatric conditions. The research found that, compared to an age-matched comparison group from the general population, IBS patients were significantly more likely to go on to develop mental-health problems such as mood, anxiety and sleep disorders.
The IBS patients even had a higher risk of developing severe, psychotic, conditions such as schizophrenia. Furthermore, the most likely time for a mental-health problem to emerge was within the first year of the IBS diagnosis.
This apparent linkage between gut and brain has fuelled a rapidly developing search for “psychobiotics” and “nutraceuticals” – foodstuffs or dietary supplements that could improve mental health via their impact on the microbiome.
Work in this area is in its infancy, but the initial results look promising. In one study, published earlier this year in the journal Bipolar Disorder, 66 patients hospitalised for the titular condition were given either probiotic dietary supplements or a placebo along with regular medication at the point of discharge. After twenty-four weeks, only eight of those receiving the supplements were readmitted to hospital, compared to 24 of those in the placebo group.
In another study, published in 2016 in the journal Translational Psychiatry, a research team looked at the impact of dietary supplements on stress and anxiety levels among healthy participants. Compared with the placebo-receiving control group, the participants who took the real supplement had lower levels of both the stress hormone cortisol and self-reported anxiety, suggesting that psychobiotics might also be used to help keep healthy people in good mental shape.
One easily digestible take-home message from all of this is that diet is as important to our mental wellbeing as it is to our physical health. If an apple a day keeps the doctor away, it might also help to keep us off of the psychiatrist’s couch.
Dr Justin Thomas is a professor of psychology at Zayed University