Probiotics: Effective link between Gut and Brain

Companies selling probiotic foods had for a long time widely popularised the benefits of cultivating healthy gut bacteria but neuroscientists had reservations about the same. Gut bacteria together in scientific parlance are referred to as microbiome. Probiotics are ingested microorganisms associated with beneficial effects to humans. These are basically good bacteria. The concept has been introduced way back in 1907 by the Nobel Laureate Eli Metchinkoff who suggested that “the dependence of the intestinal microbes on the food makes it possible to adopt measures to modify the flora in our bodies and to replace the harmful microbes with useful microbes”. It is known that digestive tract is home for trillions of bacteria and they account for 3% of the body weight. Studies show that these bacteria affect the dense network of neurons in the gut, now deemed as the second brain. A microbial imbalance in the gut or dysbiosis has been associated with chronic fatigue, obesity, physical ailments and certain types of cancer. Though the exact mechanism through which these bacteria can cause or cure the ailments is known but growing evidence has sparked greater interest among the scientists towards probiotic research.

Scientists of California Institute of Technology, Pasadena believes that bacterial waste products have an influence on the brain. Particularly the Vagus nerve that connects digestive tract to the brain might have an important role to play. Two types of intestinal bacteria are found to produce ϒ- amino butyric acid (GABA), a neurotransmitter. The new observations assume greater significance due to the dogma of nothing can cross the brain-blood barrier prevalent in the scientific community. This essentially means that brain is sealed off from rest of the body and protected from infection. But new evidence effectively shows that there is an apparent communication between the brain and the gut.

In an experiment carried out at University of Cork, Ireland found that mice born by caesarean section had a different microbial composition compared to the vaginally delivered mice. The former were more anxious and had symptoms of anxiety. Inability to pick up mother’s vaginal bacteria may have led to lifelong changes in mental health.

Mice with autism were found to have low levels of common gut bacterium Bacteriodes fragilis than the normal mice. These animals were stressed, antisocial and had gastrointestinal symptoms characteristic of autism. Symptoms were reversed when then mice were fed with B.fragilis. The stressed mice were also found to contain higher levels of bacterial metabolite 4-ethyl phenyl sulphate (EPS) in their blood. When normal mice were injected with EPS it exhibited similar behavioural symptoms as autistic mice. Though the mechanism of action is unclear, the changes in the behaviour may be outcome of a leaky gut since the chemical seeped into body through intestinal wall. These observations raise the possibility of Probiotics as a promising therapy for autism as they target gut instead of brain which is a more complex and inaccessible organ.

Currently there is a great excitement about the role played by the microbiome on the body hence large scale DNA profiling had been initiated to identify various bacterial species of the gut. Probiotics are becoming increasingly popular international organisations like FAO (Food and Agriculture Organisation) and WHO (World Health Organisation) has also validated certain of the recommendations of the probiotic research. Both the organisations have endorsed the use of probiotics as an effective ‘alternative’ besides the recommended medications for regression of psychological disorders and other body ailments.

 

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