The Microbiome, the Brain, and Obesity

uBiome - Microbiome Sequencing Gut Bacteria SampleJournals are full of information about the microbiome, and the scientific world is getting used to the idea that the bacteria inside us are related somehow to obesity, diabetes, asthma and other manifestations that are amenable to traditional metrics. Much harder to accept is the idea that the bugs influence depression, anxiety and other moods that we typically think of as originating in the brain.

Researchers have been aware, wrote Peter Andrey Smith for The New York Times, that neurochemicals like serotonin and dopamine are created in the intestine, but apparently it comes as a surprise that microbes are doing the manufacturing work. Such substances are called psychobiotics because they actually alter the mind, as demonstrated by both psychological tests and brain scans.

This is being taken seriously by, for instance, the National Institute of Mental Health, which has awarded hefty grants to people and institutions who study the role of the microbiome in mental disorders. In the pages of the journals, tantalizing hints regularly appear that point to a whole new unexplored realm.

New Revelations About the Microbiome

It seems to be more than coincidental that autism rates have been increasing along with obesity rates, and this month’s issue of Pediatrics contains news of a study of 5,053 children that showed:

Nearly a third (32 percent) of the 2 to 5 year olds were overweight, compared to less than a quarter (23 percent) of 2 to 5 year olds in the general population. Sixteen percent of the 2 to 5 year olds with autism were medically obese, compared to 10 percent of 2 to 5 year olds in the general population.

Autistic teenagers are also more likely to be obese, but the difference between them and the general population is not so pronounced. Unfortunately, this study did not account for the variables provided by diet and exercise, and it did not consider a possible relationship with the microbiome. One theory holds that relatively isolated autistic kids don’t engage in as much physical activity as their non-autistic counterparts, which undoubtedly is a factor, though perhaps not the defining or deciding factor.

The study also acknowledged that rispericone and other “behavior-calming” pharmaceuticals cause weight gain, and some very troubled kids are taking as many as five different kinds of pills. But why and how do these meds cause weight gain? Is it because they disturb the customary activities of the microbiota? Or does it go back even farther, to where autism itself is somehow caused or exacerbated by an unbalanced and disordered population of microbes in the GI tract?

A brand-new report in Current Biology documents, for the first time, “a direct link between the severity of someone’s autism symptoms and brain levels of the neurotransmitter GABA, or gamma-aminobutyric acid.” To make this part short and sweet, here is the Conclusions section of a poster addressing the subject, from Northeastern University researchers:

  • GABA is a growth factor for uncultured bacteria in the gut microbiome
  • Flavonifractor sp. is an abundant member of the gut microbiome focused on fermenting GABA
  • A number of the most abundant bacteria in the gastrointestinal tract produce large quantities of GABA
  • GABA modulation by the gut microbiome may be a mechanism of communication along the gut-brain axis
  • Introducing producers of GABA or eliminating Flavonifractor sp. could be therapeutic for mental health disorders

Obesity and autism are connected. Autism and GABA are connected. GABA and a prominent citizen of the microbiome are connected—and not only that one. As Childhood Obesity News mentioned, Dr. Sarkis Mazmanian of the California Institute of Technology has been working with another abundant species of gut bacteria, Bacteroides fragilis, and also suspects that intestinal permeability might be the issue, which circles back again to the problem of leaky gut syndrome, which is caused by yet another type of bacteria. Further, it is known that some children with autism have experienced improvement in their conditions when subjected to “restrictive diets and antibacterial treatments.”

Your responses and feedback are welcome!

Source: “Can the Bacteria in Your Gut Explain Your Mood?,”, 06/23/15
Source: “Seeking solutions, study explores autism-obesity link,”, 11/02/15
Source: “Evidence that brain-chemical imbalance drives autism symptoms,”, 12/17/15
Source: “GABA Modulating Bacteria in the Human Gut Microbiome,”, 2014
Image by Tony Webster


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About Dr. Robert A. Pretlow

Dr. Robert A. Pretlow is a pediatrician and childhood obesity specialist. He has been researching and spreading awareness on the childhood obesity epidemic in the US for more than a decade.
You can contact Dr. Pretlow at:


Dr. Pretlow’s invited presentation at the American Society of Animal Science 2020 Conference
What’s Causing Obesity in Companion Animals and What Can We Do About It

Dr. Pretlow’s invited presentation at the World Obesity Federation 2019 Conference:
Food/Eating Addiction and the Displacement Mechanism

Dr. Pretlow’s Multi-Center Clinical Trial Kick-off Speech 2018:
Obesity: Tackling the Root Cause

Dr. Pretlow’s 2017 Workshop on
Treatment of Obesity Using the Addiction Model

Dr. Pretlow’s invited presentation for
TEC and UNC 2016

Dr. Pretlow’s invited presentation at the 2015 Obesity Summit in London, UK.

Dr. Pretlow’s invited keynote at the 2014 European Childhood Obesity Group Congress in Salzburg, Austria.

Dr. Pretlow’s presentation at the 2013 European Congress on Obesity in Liverpool, UK.

Dr. Pretlow’s presentation at the 2011 International Conference on Childhood Obesity in Lisbon, Portugal.

Dr. Pretlow’s presentation at the 2010 Uniting Against Childhood Obesity Conference in Houston, TX.

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