Ask the Doctors by Eve Glazier, M.D. and Elizabeth Ko, M.D

Two Missing Gut Microbes Could Influence Mental Health

Dear Doctor: I just read about a study where people who were depressed actually had a different gut microbiome than people who weren’t depressed. Is that true? Does your gut determine how you feel?

Dear Reader: The recognition of the link between emotions and the gut is so ancient, it’s been hardwired into our language. There’s the gut feeling, going with your gut, butterflies in your stomach, a sinking feeling, bad news that’s a punch to the gut, having a gut response, or finding something to be nauseating, sickening or gut-wrenching.

Now, new research suggests that not only does the brain affect the gut, but that the connection actually goes both ways. Specifically, that the composition of the gut microbiome may play a role in how someone feels. This is a new and sometimes controversial field of research, and it is the subject of (occasionally fractious) debate.

The study you refer to may be one published in February in the scientific journal Nature Microbiology, which focused on 1,054 people from Belgium. Of those, 173 were either diagnosed with depression or did poorly on a questionnaire that asks participants to rate their quality of life.

When the composition of participants’ microbiomes were analyzed and compared, researchers found an interesting difference. Specifically, people with depression lacked two types of microbes, known as Coprococcus and Dialister, which were present in the guts of those who were free from depression.

Data in the Nature study were compared with a study of 1,064 Dutch people in which researchers found that the same two microbes were missing from the guts of those who either reported or were diagnosed with depression. In addition, the two different groups with depression had greater numbers of a certain microbe believed to be involved in Crohn’s disease.

This adds weight to the theory that inflammation has a role in mental health. The specific reason that these two missing microbes affect depression is unclear. One promising line of thought, according to the researchers, is that that Coprococcus has been linked to dopamine, a brain chemical that influences feelings of pleasure and satisfaction. The microbe also makes a substance that acts as an anti-inflammatory.

Such studies can suggest cause-and-effect relationships, but they shouldn’t be considered “proof” of a connection. They don’t prove them.

It’s fascinating that the depressed people in the studies lacked certain microbes in their guts, but more research is needed to show direct causality. The good news is that each new study adds to our understanding and sets the stage for new research to come. The hope is that, over time, this line of inquiry will lead to new therapies such as microbiome profiling or precision bacterial supplements, which will offer new avenues of relief to people living with depression.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)