SINGAPORE — The importance of the gut to physical health is well known. Now, an emerging field of research has found that the trillions of microorganisms living in the digestive tract, known as gut microbiota, can communicate with the brain too.
Tweaking this gut microbial balance through the use of a new class of probiotics known as psychobiotics, for instance, could tip it in favour of better mental health, some experts believe.
Psychobiotics are “a game changer” that could potentially provide new treatments for conditions such as depression, Parkinson’s disease and autism, said Professor Tsai Ying-Chieh of the Institute of Biochemistry and Molecular Biology of National Yang-Ming University in Taiwan at the Vitafoods Asia conference held here earlier this month.
The effect, according to experts, could occur though several pathways, including the nervous system — the spinal cord or the vagus nerve, which connects the brain to the digestive tract — small molecules produced by gut microbes, as well as through the immune system and hormones within the gut.
“This concept surfaced only in the past five to six years. Before that, nobody would believe that your gut microbiota could influence your brain,” Prof Tsai told TODAY on the sidelines of the conference.
Findings from preliminary research have been promising. In studies on animals, Prof Tsai and his team found a novel psychobiotics strain, known as Lactobacillus plantarum PS128, could alter the brain chemistry of mice, such as by raising dopamine levels.
Dopamine is a chemical messenger that transmits signals between brain cells and lowers stress hormones and depression-like behaviour.
Low levels of dopamine are linked to low mood, depression, as well as neurological conditions such as Parkinson’s disease and attention deficit hyperactivity disorder. Elevated levels of stress hormones in the long term can interfere with learning, memory and may lower immunity, said Prof Tsai.
Lactobacillus plantarum PS128, extracted from a Taiwanese traditional fermented mustard, has been tested on humans. This year, Prof Tsai and his team wrapped up a study involving 80 boys aged seven to 15 and diagnosed with autism spectrum disorder. The study was placebo-controlled and double-blind, where participants and researchers did not know which participants belonged in the test or the control groups.
WHEN GUT BALANCE IS DISRUPTED
Prof Tsai said his team observed “improvements in symptoms such as compulsive repetitive and disruptive behaviour” and will submit its findings next month.
The team is in the midst of two more clinical trials in Taiwan to study the effects of PS128 on major depressive disorder and movement disorders including Tourette Syndrome (characterised by repetitive and involuntary movements and vocalisations called tics) and Rett Syndrome (a rare genetic disorder that affects brain development and results in severe mental and physical disability).
Just as increasing good gut bacteria could benefit mental health, the opposite effect could also occur when beneficial microbes in the gut are depleted.
“For instance, we know that taking too much antibiotics can affect gut microbiota balance, which may cause the immune system to go haywire. If the child takes too much antibiotics in the early stage of his life, during which rapid brain development occurs, an unhealthy gut microbiota may affect or change how his brain develops. But this is still a hypothesis,” said Prof Tsai.
Other environmental and lifestyle factors that may upset the balance include work stress and sleep deprivation, said Associate Professor Lee Yuan Kun of the Department of Microbiology and Immunology at the National University of Singapore.
Animal studies have also found that early mother-and-child separation may induce depression symptoms, which could be improved through the right gut microbes, said Assoc Prof Lee, who spoke on gut microbiota at the conference.
However, doctors will not be prescribing psychobiotics to treat mental disorders any time soon.
There is currently no strong clinical evidence to suggest any particular food or dietary supplements can improve mental disorders, said Adjunct Associate Professor Daniel Fung, chairman of the Medical Board at the Institute of Mental Health.
That said, he does not discourage the use of dietary supplements as part of a balanced diet, as long as there is no harm to one’s health.
Most existing studies have been done on animals and it could take another five to 10 years to complete human clinical trials, said Assoc Prof Lee.
“Currently, dietary probiotics are not allowed by law to claim that it has clinical effects. (For it to claim clinical effects), it would have to be marketed as a drug,” he said.
More research is also needed on how best to use psychobiotics — for instance, which specific strains to use, and in what amounts, to improve mental health. So far, there are published studies on only five to six strains of probiotics, said Prof Tsai.
“It is not as simple as taking some yoghurt or fermented food,” he said. “For instance, in the autism study, the children take high doses of Lactobacillus plantarum PS128, which are impossible to obtain if you were to consume fermented mustard directly.”
In the meantime, individuals can maintain good gut health through a varied and balanced diet, said Assoc Prof Lee.
A common mistake people make is to consume too much of a few good things, such as salmon, and reject foods that are “not good enough”, he said.
Some studies, including one published in the peer-reviewed journal PLoS ONE in 2011, show that people who consume a balanced diet generally have lower rates of mental health issues.
A diverse and balanced diet helps provide the necessary nutrients for microbes in the gut, which generally feed on whatever their hosts eat, but draw from different components of the diet so that they do not compete for nutrients, he said.
Consumers should also eat less processed foods. This is because they tend to contain artificial flavours which have no nutritional value, and lack fibre and roughage (found in the bran of cereal, for example) which are a good food source for gut microbes, said Assoc Prof Lee.