Recent years have seen an increase in the amount of research examining the connection between gut bacteria and stress-related disorders such as anxiety, depression and irritable bowel syndrome. Exposure to stress can cause major changes in the functioning of the gut and brain, which can in turn trigger behavioural alterations.
Short-chain fatty acids lower stress reaction
In this latest study, scientists at APC Microbiome Ireland at University College Cork and Teagasc Food Research Centre found that there were decreased levels of stress and anxiety-like behaviour when short-chain fatty acids (SCFAs) were introduced to the gut.
Bacteria in the gut naturally produce SCFAs, which are the main source of nutrition for cells in this region of the body. High fibre foods such as grains, legumes and vegetables stimulate the production of these SCFAs, the researchers noted.
The study involved feeding mice the main SCFAs normally produced by the gut bacteria and then subjecting them to stress. Using behavioural tests the mice were assessed for anxiety and depressive-like behaviour, stress-responsiveness, cognition and sociability as well as how easily material passes through the gut.
The researchers also noted stress experienced over a prolonged period can affect the bowel by making the barrier between the inside of the gut and the rest of the body less effective and “leaky”. This means undigested food particles, bacteria and germs will pass through the leaky gut wall into the blood and cause persistent inflammation. Treating with the SCFAs can also reverse this “leakiness”, the team suggested.
These results provide new insights into mechanisms related to the impact of the gut bacteria on the brain and behaviour as well as gut health. Developing dietary treatments targeting these bacteria will be important for treating stress-related disorders, the APC Microbiome and Teagasc researchers said.
Mechanism remains a mystery
While the researchers said their study provides further evidence of the link between gut health, diet and depression, the exact mechanisms by which SCFAs facilitate their effect remain undetermined.
SCFAs had no effect on an increase in body weight caused by stress therefore understanding why SCFAs only affect certain stress-induced effects will be important, the study suggested.
Professor John Cryan, the corresponding author on the research, commented: “There is a growing recognition of the role of gut bacteria and the chemicals they make in the regulation of physiology and behaviour. The role of short-chain fatty acids in this process is poorly understood up until now. It will be crucial that we look at whether short-chain fatty acids can ameliorate symptoms of stress-related disorders in humans.”
Source: The Journal of Physiology
doi: 10.1113/ 276431
“Short-Chain Fatty Acids: Microbial Metabolites That Alleviate Stress-induced Brain-Gut Axis Alterations”
Authors: Van de Wouw et al.