Happy Gut, Happy Human :)
Before 1950, mental illness was more often than not treated surgically. Testimony to this fact was that in 1945 the Nobel prize was awarded to the inventor of the lobotomy. But even pre-lobotomy the removal of the colon was the most common form of treatment for mental illness. This was because the strongest theory of the time was that bad bacteria in the intestine caused sickness of the mind, something that has now been confirmed through the modern scientific method. Though one in three people died from the surgery, the ones that didn't were said to be cured. Thankfully, there were others that took less severe measures and instead of giving colectomies, offered probiotics to their patients. All of this came about through the observations of the doctors at the time who noted that their depressed patients also had faeces deficient in quantity and moisture, and that were often "very offensive in odour". As a result of such observations, all patients were prescribed a vegetarian diet. This, it was reported, produced wonderful results.
Until recently, due to the emergence of a relatively new discipline called "enteric (intestinal) neuroscience", no further discoveries or progress was made in this field. Thankfully however, enteric neuroscience now recognises the gut as our second brain due to its similarity in size, and neuronal complexity. This shouldn't come as any surprise when we consider, for example, the experience of 'butterflies in the stomach'. It's probably clear to most of us that our mental state creates sensation in the gut, but what might not be so immediately apparent, is that our gut also affects our mental state.
The health of our gut flora or microbiome has been shown to effect not only our physiological health but also our mental state. The application of probiotics to people with chronic fatigue syndrome has, for example, been shown to relieve symptoms a great deal. But what really shocked the medical establishment was the study of the affects of probiotics in healthy people. Here it was found that just one month of probiotics significantly decreased anxiety, depression, anger, and hostility. Following this, various mechanisms have been proposed to explain the effect of intestinal bacteria on the brain, and emerging out of this are a variety of possible treatments such as faecal transplant from the contented folk to the less contented folk, and the prescription of different probiotic formulas.
There have also been many studies on emotional/mental states being affected positively by plant-based diets and negatively by the consumption of animal products. In fact, in 2014 a systematic review and meta-analysis of dietary patterns concluded that diet undoubtedly affected mood. But more interesting was that only one out of the 21 studies found in the medical literature was an actual randomised control trial (considered the study that provides the highest degree of evidence), and that it concluded that removing animal products improved mood in only two weeks. Further studies, also conclude a vegan diet 'appears to be unique in several characteristics, including a reduced abundance of pathobionts (disease causing organism), including 'Enterobacteriacea..., and a greater abundance of protective species such as F. prausnitzii....Vegans also appear to lack the intestinal microbiota for converting dietary l-carnitine into the proatherosclerotic TMAO... [leading to less] inflammation [which]may be the key feature linking the vegan gut microbiota with protective health benefits'.
This is most relevant because if there is one certainty in all this it's that the state of one's microbiology can lead to inflammation, and inflammation of the gut is increasingly associated with depression, anxiety, and clarity of thought. For example, a study that followed 43,000 women without depression, and closely regarded their dietary habits for 12 years, made clear associations between the intake of inflammatory foods such as meat, sodas, refined grains, and the subjects who became depressed.
In fact, every day more evidence is emerging that suggests eliminating animal products and increasing our fruit and vegetable intake increases the health of our microbiome, which in turn leads to less inflammation of the gut, and thus better health and better mood.
Amazingly then, we can conclude that we may be able to prevent depression and anxiety through what we put into our bodies, and that the state of our gut significantly affects the state of our minds!