The bacteria that live in our gut are as numerous as the cells in our body. As medical research progresses, the influence that these billions of tiny creatures have on our health is becoming ever more apparent.
It comes as no surprise that they might play a role in gastrointestinal issues, but the microbiome's influence flies much further afield.
Stress, the gut, and the brain
Although the thought of a microorganism in our intestines affecting our mental well-being seems like a leap, the gut and brain are deeply entwined. As an example, most people will know how a nerve-wracking situation can influence the speed of our bowels and, vice versa, how being hungry can cast a shadow over our mood.
A troubled brain can inform the gut, and a troubled gut can inform the brain.
Stress, although it is a mental state, can physically affect our gastrointestinal system and the bacterial residents within it. A recent study found that high levels of stress can affect gut bacteria to a similar degree as a high-fat diet; while other studies have shown that reducing the number of bacteria in the gut can produce stress-induced activity in mice.
So, it seems that the road runs both ways: stress can alter gut bacteria, and gut bacteria can influence stress levels. It is a complicated web.
A recent piece of research, published in The Journal of Physiology, takes a fresh look at how gut bacteria are involved in gut health problems induced by stress. The work was carried out at APC Microbiome Ireland at University College Cork and Teagasc Food Research Centre in Ireland.
The role of SCFAs
The team of scientists was interested in short-chain fatty acids (SCFAs). Gut bacteria produce SCFAs when they digest fiber; the cells of the colon then use SCFAs as their primary source of energy, making them vital for good gut health.
The researchers found that when they introduced SCFAs to the guts of mice, stress and anxiety-based behaviors were significantly reduced.
After demonstrating that SCFAs reduce anxiety, they wanted to understand how these small molecules influenced physical, stress-related gut damage.
Known as a "leaky" gut, high levels of stress over time increase the intestine's permeability. This means that particles, such as bacteria and undigested food, can move more easily into the bloodstream, which can cause damaging chronic inflammation.
The researchers found that by introducing SCFAs, they reduced the gut leakiness caused by persistent stress.
"There is a growing recognition of the role of gut bacteria and the chemicals they make in the regulation of physiology and behavior. The role of short-chain fatty acids in this process is poorly understood up until now."
Lead author, Prof. John F. Cryan
What does it all mean?
Fruits, vegetables, and grains naturally contain high levels of fiber. Although this study was conducted on mice, the inference is that a high-fiber diet might prompt gut bacteria to produce more SCFAs — thereby bolstering our gut's natural defenses against the damage caused by stress.
Of course, plenty more research will be necessary before that conclusion can be written in stone; as Prof. Cryan says, "It will be crucial that we look at whether short-chain fatty acids can ameliorate symptoms of stress-related disorders in humans."
Future work will also need to dig deeper to get a better understanding of exactly how SCFAs provide these benefits. Unwrapping the molecular shenanigans behind the scenes is likely to be challenging.
The authors hope that the current findings will, eventually, help in the "development of microbiota-targeted therapies for stress-related disorders."
However, for now, attempting to minimize stress in one's life while upping consumption of fruit and veg is likely to be a sensible recommendation, whether it impacts levels of SCFAs or not.