The intestinal flora is also affected by chronic stress. The increased release of stress hormones can reduce the biodiversity of the bacteria living in the intestine and cause a decrease of the useful lactic acid producing bacteria (lactobacilli and bifidobacteria). The food consumed becomes more difficult to digest due to the decrease in bacteria, which can initially result in abdominal pain and later in diarrhoea or vomiting. In addition, when the lactic acid-forming bacteria decrease, the pH value of the intestinal environment shifts and thus offers less resistance to unwanted bacteria.
However, the stress-induced, slowed-down gastrointestinal passage can further shift the bacterial balance in the intestine: Putrefactive bacteria can displace useful bacterial strains such as lactobacilli and bifidobacteria. The latter are significantly involved in the production of the amino acid tryptophan, which is needed for the production of serotonin. A decrease in bifidobacteria can thus also manifest itself in a serotonin deficiency. The consequence: stress resistance decreases even further.