Hippocrates, the father of modern medicine, famously declared 'all disease begins in the gut'. 'Let food be thy medicine, and let medicine be thy food,' he urged his followers. Two thousand years later, it seems that science is beginning to catch up with him, as increasing evidence is emerging of the vital role that the gut, and more specifically, the microbiota – the trillions of bacteria, viruses, fungi and other organisms living within it – have on our mental and physical wellbeing.
Advances in medicine, such as the development of broad-spectrum antibiotics, have certainly saved lives. Belatedly, however, scientists are recognising that their effect on the microbiota can be less beneficial. It's known that, for instance, infants given antibiotics have a higher risk of developing asthma, childhood obesity and coeliac disease. Now, it is being suggested that the soaring rates of clinical depression may also be linked to the stresses that modern existence puts on the gut's unique 'microbiome'.
The gut is known as the body's 'second brain' for good reason. The two are hard-wired together by the vagus nerve and, surprisingly, there is far more communication from the gut to the brain than the other way around. Furthermore, it is in the gut that we manufacture the majority of our serotonin, the neurotransmitter that contributes to feelings of happiness, with certain bacteria in the gut important for its production.
According to the clinical nutritionist Stephanie Moore: "Some say there's no way that serotonin gets to the brain; more people are saying, "It must do, but we don't know how." We can't manufacture serotonin in the brain in the way we do in the gut. This is brand-new stuff." All of which raises the intriguing possibility that in the future, depression could be treated with diet rather than pills.
So can you eat yourself happy? Of course – temporarily – as anybody who has ever perked up a low mood with chocolate or drowned their sorrows in a glass of wine will know. However, such easily absorbed carbohydrates are damaging in the long term, causing spikes in blood sugar and feeding unhealthy gut organisms, such as the yeast candida albicans, at the expense of beneficial bacteria. "Foods and drinks that are sugary, heavily processed or alcoholic are known depressives, despite their allure in times of stress," says the nutritional therapist Amelia Freer. While, according to the clinical nutritionist Peter Cox, "a lack of B vitamins, vitamin D and omega-3 are common contributors to mental-health disorders."
Conversely, a study of more than 15,000 people published last year showed that adopting a Mediterranean diet, high in vegetables, fruit, beans, nuts and olive oil, and low in processed foods, could prevent the onset of depression. "To feed a wide variety of microbiota you need a diet rich in plant compounds, fruit, vegetables, oily fish, not too much red meat, and to avoid junk food. This diet is good at lowering inflammation and therefore likely to have an effect on mood," says Professor Graham Rook, an emeritus professor of medical microbiology.
Eggs, which contain tryptophan, needed in the production of serotonin, and wild salmon, full of healthy fatty acids, are well-known mood boosters. Fermented products, such as kimchi, sauerkraut, olives and pickles are also happy foods. Naturally rich in probiotics, they also aid digestion, support immune function, and have been shown to boost mood and reduce levels of the stress hormone cortisol. On the popular seven-day Health Regime at Grayshott Spa, designed by Moore to heal the gut and boost beneficial bacteria, every meal starts with a glass of digestive bitters and a spoonful of fermented cabbage. Starchy carbohydrates are eliminated, along with sugar, grains and caffeine, while vegetables, protein and good fats take centre-stage. Participants are also given a water-based probiotic, Symprove, which contains a mixture of beneficial live bacteria that survive the digestive transit.
I joined the regime for just 24 hours, but afterwards continued loosely to follow the diet on my own and to take Symprove daily. After a few weeks, as well as having a flatter stomach, I've noticed that I feel calmer and happier. Of course, it's far too early to be sure that the change in my diet is the cause of the improvement in my mood, but so far, I'm with Hippocrates.