Although the aetiology of depression, schizophrenia and other psychiatric disorders have been extensively studied for many years, the exact causative agents have not been established. It was well described that the patomechanism includes biochemical imbalance in the brain, but was not established what is the key factor directly causing these alterations. These diseases have strong genetic background, but may also be originated from chronic inflammation within the body. Currently the scientists consider whether the increasing prevalence of psychiatric disorders may be linked to diet – a nutrition of western style, thus rich in fat and sugar, and low in fiber. Such diet, when combined with a number of other disbiotic factors: drug abuse, stress, addictions have a deleterious impact on junctions between enterocytes and lead to the development of the leaky gut syndrome. The loss of intestinal barrier integrity leads to the penetration of undigested food molecules, toxins, microorganisms and other potentially harmful antigens into the circulatory system. As a consequence, the immune system is activated – to eliminate these harmful substances. However, this can not be done, because the cause – the damaged intestine – still exists. As a consequence, chronic inflammation develops, gradually involving more tissues and organs.
The inflammation (local or systemic) is considered to be a factor favouring the development of psychiatric disorders, and scientists find an increasing amount of evidence to support this theory (the so-called inflammatory hypothesis of depression). During inflammation level of specific mediators, so-called proinflammatory cytokines, increases. Studies conducted in patients with schizophrenia and depression showed that the increase in proinflammatory cytokines is strongly correlated with the occurrence of the disease episodes. At the same time, in healthy subjects, without psychiatric disorders, these cytokines are not synthesized at all. This makes a strong relationship between inflammation and the development of depression and schizophrenia. In other words, chronic inflammation has a negative impact on brain function, most likely affecting brain’s reward and punishment circuits.
Depression may also develops in patients receiving drugs stimulating the secretion of proinflammatory cytokines, as typically observed in cancer patients receiving anti-neoplasia therapies and in patients treated for autoimmune disorders. Similarly, an anti-inflammatory agents implemented together with antidepressant therapy, make therapeutic effects to occur faster and be more satisfactory. For this reason, therapy targeted on the prevention of the intestinal barrier integrity, proper diet, both eliminating causes and symptoms of inflammation, should be an integral part of classical treatment. Many studies have been published to indicate a direct connection between intestinal barrier damage, IgG-dependent allergy development, activation of inflammatory traits and subsequent depression development. Performing tests for latent food hypersensitivity (IgA and IgG – dependent) and tailored dietary treatment may significantly improve clinical course in this group of patients.
We should never forget about the role of intestinal microflora in maintaining adequate gut barrier integrity. Moreover, intestinal bacteria, producing a number of metabolites, directly affect the brain structure and functions via gut-brain axis. It is a bidirectional communication pathway, connecting the intestine and gut microbiota to the central nervous system. Gut microbiota directly affects the level of pro-inflammatory cytokines, controls the production of neuromediators (chemicals affecting the brain), and synthesizes substances that elevate the intestinal barrier integrity. The dysbiosis is therefore proposed as a possible causative agent of neuropsychiatric disorders. It has been shown that appropriately selected probiotic strains (so-called psychobiotics) significantly improve mood and behaviour. In patients with psychiatric disorders, an evaluation of the gastrointestinal barrier integrity (zonulin) should be considered, followed by food hypersensitivity examination (IgA and IgG – dependent) both proved to activate inflammation. Implementation of a targeted elimination diet and probiotic therapy reduces inflammation in the body, which may improve the condition of patients.
In case of depression, schizophrenia and other psychiatric disorders, the following tests are recommended: