Bowel problems and bladder
The gut microbiota is the collective term for the rich ecosystem inhabited by trillions of micro-organisms living both in and on humans. Over the last two decades, research on the gut microbiota has been on the rise and it is now clear that it is a key determinant of human health and an important regulator of host physiology. The human microbiota is thought to be highly diverse, dynamic and sensitive to external stimuli, making it a potential and promising target for various therapeutic interventions (Cryan et al., 2019).
There is hardly a niche of the human body that is not inhabited by a different ecosystem of bacteria, viruses, fungi and other micro-organisms, yet the largest areas of microbial colonisation on the human body are: the skin, the respiratory tract, the eyes, the genitourinary tract and the gastrointestinal tract. Despite the importance of the respiratory and oral microbiota, most emphasis in academia is placed on the gut microbiota because of its impact on various brain processes. Whereas research on the brain-gut axis initially focused on the regulation of digestion and satiety, most of the focus today is on higher-level cognitive processes and the pathopsychological effects resulting from the breakdown of communication between the two. Impairment of the brain-gut axis is thought to increase the risk of autism spectrum disorders, depression, schizophrenia, eating disorders and anxiety, among others (Finegold et al., 2012; Foster and McVay, 2013; Horne and Foster, 2018; Kleiman et al., 2018; Severance et al., 2015).
Effects of diet on the brain-gut axis
Diet is one of the critical factors that regulates the composition of the gut microbiota and has a concomitant effect on our brain and behaviour. The effects of diet are so dramatic that huge changes in gut microbiota composition can occur in as little as 24 hours when individuals change their diet from an animal-based to a more plant-based diet and vice versa (David et al., 2014).
Gut micro-organisms are involved in the digestion, absorption, metabolism and breakdown of undigested micronutrients, which has many positive and beneficial effects for the host.
Carbohydrates
The most researched micronutrients are carbohydrates, more specifically dietary fibre. Dietary fibre is a non-digestible substance that is most concentrated in whole grains, vegetables, fruits, legumes, nuts, seeds and potatoes. They are an important part of a balanced diet because of the fermented by-product that results from their breakdown by the microbiota in the large intestine. This fermented by-product is short-chain fatty acids, which play an important role in maintaining immune homeostasis and protecting us from inflammation and carcinogenic influences. Short-chain fatty acids can reach the brain by crossing the blood-brain barrier, but their effect on psychological processes is not yet fully understood (Zmora et al., 2018).
Vitamins and minerals
Vitamins and minerals belong to the second group of micronutrients and play a key role in the synthesis and metabolism of neurotransmitters, whose main function is to transmit messages between nerves. The gut microbiota is thought to synthesise mainly vitamin K and a group of B vitamins, with which, in addition to minerals, it has a symbiotic relationship. Many gut bacteria require minerals for growth and development, so deficiencies or excess concentrations of minerals can lead to microbial imbalances and the proliferation of many pathogenic microbes (Zmora et al., 2018).
Polyphenols and fermented foods
Polyphenols are powerful oxidants that protect our bodies from oxidative stress and free radicals. They are found in fruits and vegetables, cocoa beans, nuts, cereals, spices, red wine, coffee and green tea. 90-95% of polyphenols cannot be absorbed by our bodies, so they are further broken down by microbes in the gut. Eating foods rich in polyphenols has many positive effects on our health. From anti-inflammatory and antioxidant effects, to improved cognitive function in both older and younger populations (Bastienatto et al., 2015; Devore et al., 2012; Gildawie et al., 2018; Philip et al., 2019).
Kombucha, yoghurt, sauerkraut and kimchi are just a few examples of fermented foods whose consumption is associated with maintaining a healthy weight and a reduced risk of diabetes, cancer and many cardiovascular diseases. The Stanford study investigated the effects of a high-fibre diet and a high-fermented diet on gut diversity and the immune system of healthy adults. They found that the high dietary fibre diet improved gut microbiota function, while immune responses were highly individualised. Alternatively, a diet high in fermented products increased microbiota diversity and reduced inflammatory factors, thus having a positive effect on both parameters measured (Díaz-López et al., 2016; Gille et al., 2018; Mozaffarian et al., 2011).
Bladder problems
Patients may also experience functional bladder problems. These symptoms may manifest in:
Urinary dysfunction (inability to urinate or difficulty starting to urinate)
Frequencies of urination
Urges to urinate
Occasional difficulty holding urine
Chronic urinary retention
"Urinary retention is the acute or chronic inability to voluntarily pass an adequate amount of urine." (Serlin et al., 2018). The disease predominantly affects men, the causes are complex and relate to iatrogenic, neurological, inflammatory and infectious causes. Chronic urinary retention is usually not of neurological cause and is asymptomatic.
Cauda Equina Syndrome
Cauda equina syndrome is caused by dysfunction of several sacral and lumbar nerve roots in the lumbar spinal canal. Signs and symptoms include low back pain, pain spreading down the leg, numbness around the anus and loss of bowel or bladder control (Orendáčová et al., 2001).
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