What is the Gut-Brain Axis? Can What We Eat Affect How We Feel?

What if I told you that there is a kind of neglected organ-hub in your body that weighs just as much as the brain, and in some ways is just as important to our survival but is treated with disregard and we’re just beginning to understand how it works? Turns out we do have something like that, our gut, or rather it’s microbes.

The idea that the trillions of microbes that live on/in our bodies, especially the ones in the gut can affect how we function (re)gained momentum in 2004. A study in Japan led by Nobuyuki Sudo showed that when exposed to an external stressor, mice with microbe-free gut had a measurably exaggerated response to the stressor as compared to mice with their gut microbes left in-tact (Postnatal microbial colonization programs the hypothalamic-pituitary-adrenal system for stress response in mice, J Physiol, 2004). Studies like the one carried by Sudo et. al. sparked great interest in a concept called “The Gut-Brain Axis”, an idea that the microbes in our intestine can vastly effect the way our brain and nervous system function. 

But what might seem as a recent scientific breakthrough has been a known concept around the world. Cultures around the world have known that certain food, specifically called “probiotics” encourage healthy gut flora (Yogurt, Pickles, Lassi from the vedic culture; Kefir and Sauerkraut from the roman culture; Natto and Kimchi from far-east cultures).

So what gained scientific momentum as a concept recently, is certainly not new knowledge but let’s look at some recent research in the field of microbiome/gut-brain axis and discuss it’s implications.


(Sauerkraut, Pickles and Yogurt, common probiotic treats, image from http://www.eatthis.com/best-and-worst-probiotic-foods)

Recently it was identified that individuals with neurodevelopmental disorders, including autism spectrum disorder (ASD), have gastrointestinal (GI) abnormalities including heightened GI distress that might contribute to the pathophysiology of autism itself. In a mouse model of autism features, it was shown that treatment with a healthy probiotic bacterium Bacteroides fragilis alters the composition of the gut-microbiome, reduces GI-distress, improves gut-epithelial integrity and ameliorates specific autism-related behavioral abnormalities (Microbiota modulate behavioral and physiological abnormalities associated with neurodevelopment disorders, Cell, 2013).

On a similar note, Ted Dinan and his group showed that taking stool samples from humans with depression and transferring (a portion of) them into normal rats had a significant behavioral impact on the rats. The so called “melancholic microbes” from the depressed patients changed the behavior of the carefree rodents. The formerly asymptomatic rodents soon began showing signs of depression and anxiety, like forgoing sweet water treats, showing heightened anxiety response in a variety of behavioral tests whereas rats that got a microbiome from a person without depression showed no changes in behavior.


(microbiome and the brain artwork: http://www.wbur.org/npr/218987212/microbiome)

In some of the more complex and more recent studies researchers also convinvingly demonstrated that diurnal oscillations in microbial localization & activity that take place in our gut have a deep impact on circadian rhythm and function of distant tissues such as the liver and even the whole body (Microbiota Diurnal Rhythmicity Programs Host Transcriptome Oscillations, Cell, 2016). It was long held that the body has an internal clock that is maintained in the suprachiasmatic nucleus (SCN; a bilateral nerve cluster of about 20,000 neurons is located in the hypothalamus, where it receives input from specialized photosensitive ganglion cells) which responds to light availability. But by altering the diurnal rhythms of microbial activity, researchers were able to disrupt circadian patterns of organ and whole body function showing that there is a way more complex relationship shared by us and the microbes we harbor in our gut than previously understood. That changing gut microbial activity pattern independent of light availability to the whole body has an impact on our circadian rhythm of the body was an astonishing find.

While studies demonstrating that altering the gut microbiome can alter how we feel/behave/sleep have been published and gained press, a lot still needs to be uncovered. We don’t yet know how a condition like depression/anxiety/insomia (or other neurological disorders) actually alters the microbiome (by what mechanism), how long does it take for the microbiome to be altered so that it starts contributing to the pathophysiology of the condition, can altered microbiome due to our food choices be a driver of certain neurological states (the classic chicken or the egg scenario)?

To sum it up, while studies have shown that the right bacteria in our gut could brighten our mood and perhaps even combat pernicious mental disorders while the wrong kind, might lead the brain health in a darker direction, we are only beginning to understand the implications of the symbiotic relationship we have with our gut dwellers.

So the next time, you feel you eat something and it makes you feel lazy, unhappy, sleepy, or tired, there might be more going on than you might think. Think about food choices in context of how you feel, but more importantly, think about eating a balanced diet and everything else will fall into place. In the meantime if you’re looking to culture your gut with some happy, healthy bacterial folks you can go to this link https://draxe.com/probiotic-foods/ and have your pick.

BUT most importantly, trust your gut feeling.

Arpit Sharma

PhD Candidate, University of Iowa.


2 Comments Add yours

  1. Rashmi says:

    Is it really possible that ASD or even depression can be ameliorated by probiotics treatment.


    1. If by ameliorate you mean made less severe, then I think there is growing scientific evidence that probiotics treatment can help. There was also a recent study in humans in which probiotic pills were given to humans and the affect was compared to placebo and the outcomes were mood, stress and such. On the other hand if by ameliorate you mean, they can be treated, then potentially not fully with just probiotics.


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