Happy Gut, Happy Brain? Truth and Hype in the New Gut–Brain Research

[david_myers]

Psychological science delights us with its occasional surprises. For example, who would have imagined that

• electroconvulsive therapy—shocking the brain into mild convulsions—would often be an effective antidote to otherwise intractable depression?
• massive losses in brain tissue early in life could have minimal later effects?
• siblings’ shared home environment would have such a small effect on their later traits?
• after brain damage, a person may learn new skills yet be unaware of such?
• visual information is deconstructed into distinct components (motion, form, depth, and color), processed by distinct brain regions, and then reintegrated into a perceived whole?

The latest who-would-have-believed-it finding is that the microbiology of the gut may influence the moods of the brain. Digestive-system bacteria reportedly influence human emotions and even social interactions, perhaps by producing neurotransmitters. Moreover, we are told (such as here and here), healthy gut microbes can reduce anxiety, depression, and PTSD.

New articles on this supposedly “revolutionary” and “paradigm-shifting” microbiota-gut-brain (MGB) research are accumulating, report Katarzyna Hooks, Jan Pieter Konsman, and Maureen O’Malley in a forthcoming (yet-to-be-edited) review. By comparing rodents or humans with or without intestinal microbiota, researchers have indeed found “suggestive” effects on how organisms respond to stress and display emotions. Some researchers are exploring microbiota-related interventions (such as with probiotics versus placebos) as a possible treatment for depression, anxiety, and anorexia nervosa.

The findings are intriguing and worth pursuing but haven’t yet definitively demonstrated “the impact of the microbiota itself on behavior,” say Hooks, Konsman, and O’Malley. Nevertheless, the popular press, sometimes aided by university press offices, has hyped the research in more than 300 articles. People love the news of this research, say Hooks et al., because it lends hope that a natural, healthy diet can provide a simple DIY solution to troubling emotions.

Reading this analysis triggers déjà vu. This cycle of (a) an intriguing finding, followed by (b) hype, followed by (c) reassessment, is an occasional feature of our science’s history. Mind-blowing experiments on people with split brains yielded (a) believe-it-or-not findings, leading to (b) overstated claims about left-brained and right-brained people, which (c) finally settled into a more mature understanding of how distinct brain areas function as a whole integrated system.

Despite the “large helpings of overinterpretation” and the overselling of “currently limited findings,” the Hooks team encourages researchers to press on. “We see MGB research as a field full of promise, with important implications for understanding the relationship between the brain and the rest of the body.” The body (brain included) is one whole system.

(For David Myers’ other weekly essays on psychological science and everyday life visit TalkPsych.com)