The Gut-Brain Axis and How What We Eat Affects How We Feel

Recently I had the opportunity to visit Oxford and London with my Art in Science cohort. Several parts of our time there contributed to my ongoing microbiome research and they were all displayed to the public in different ways, including a lecture, performance art, and a museum exhibit. In the following three posts I will reflect on each of these as they relate to my research and art-science collaborations as a whole, beginning with the lecture I attended.


While in Oxford, I attended a lecture given by Dr. Philip W.J. Burnet entitled “The Gut-Brain Axis and How What We Eat Affects How We Feel.” I was excited to be part of the crowd at this lecture, as it coincides quite well with my area of research.


Dr. Burnet began by explaining the difference between probiotics and prebiotics (if you are unsure of the difference, check out my earlier blog post here). Prebiotics include foods such as lentils, green peas, chickpeas, and garlic. He went on to explain how the gut-brain axis regulates food intake through hormonal feedback loops. For example, a nutrient-sensing G-protein-coupled receptor (basically, a gut “taste receptor”) in an intestinal L-cell will elicit a hormonal response, which will be picked up by the vagus nerve, which will send a signal up to the brain stem, and from there to the hypothalamus. The hypothalamus is a part of the brain that regulates increase and decrease in food intake. The brain and the gut are “talking” to each other via the vagus nerve, and this is a two-way conversation. While the brain will send neurotransmitters such as serotonin and dopamine to the gut, the gut microbiota can respond with serotonin, as well as leptin. Since the gut bacteria are in intimate physical contact with the intestinal walls, they affect the intestinal feedback to the brain.

photography of garlic on wooden table
Photo by Skitterphoto on

Contrary to popular belief, there are not actually twice as many bacterial cells than human cells in the human body. According to Dr. Burnet, recent research reveals that there are actually about 1.3 times as many bacterial cells than there are human cells. The most well-known “friendly” bacteria are Lactobacillus and Bifidobacterium (both of which I have previously come across in my research). But even “unfriendly” bacteria live in the human gut normally; they are just kept at bay by the other bacteria. The basic difference between good and bad bacteria is the type of coats they wear: bad bacteria wear coats that elicit a “pro-inflammatory” response, while good bacteria do not. High fat, high sugar diets promote the growth of the former kind of bacteria, while high fiber diets promote the growth of good bacteria. Bacteria affect the way the gut responds to the food it is fed, and thus influence the brain through the gut-brain connection


The novel part of probiotic studies is not that they make us healthier, but that they improve our mood. The first study to show a connection between gut bacteria and mood was with germ-free mice. These mice had been cleansed of all of their bacterial colonies and showed lower sociability and higher stress response. Upon addition of good bacteria, the mice became more sociable and less jumpy.


Since the germ-free mice study, probiotics have shown themselves to help improve mood in patients with chronic fatigue syndrome. They also appear to improve metacognition in patients with MDD. That means probiotics not only affect our mood but how we think about our mood, which is a form of metacognition.


Prebiotics have been shown to reduce anxiety, improve problem solving abilities, and possibly even optimize metabolism. They can even cause waking cortisol levels to decrease, much like an antidepressant. Schizophrenia can be affected by gut bacteria. Patients who took prebiotics noticeably improved in basic cognitive assessments, which led researchers to wonder if the same could be true for patients with dementia.

pre- and post-supplement waking cortisol
Waking cortisol levels (blue) noticeably  decreased with GOS prebiotic supplement. Find full article here

I found it particularly interesting to learn how probiotics break down other chemicals. Pomegranates contain chemicals that are good for the brain but cannot normally cross the blood-brain barrier. However, the addition of probiotics has been shown to break down the chemicals enough that they may cross the barrier and deliver their benefits to the brain. This goes to show that while one single food or ingredient probably won’t save you (for instance, a pomegranate), making it part of a healthy, balanced diet (in this case, one that includes probiotics) can indeed deliver a health benefit.

sliced pomegranate
Pomegranates contain chemicals that are good for the brain

I was curious what others are saying about food and mood, so I did some cursory reading of online sources. In so doing I was bombarded with many so many different articles claiming that different diets could beat depression, that I think if I was someone seeking help in that area, I would have become overwhelmed by trying to discern which of these diets I should try. I am skeptical of most lists that have titles sounding anything like “eat these 10 foods every day to beat depression,” as different people may respond to the same food product in different ways. However, a recurring theme seems to be that eating more leafy greens and seafood and less sugary and processed food is generally helpful. I cannot help but wonder if leafy greens and seafood were presented as mood-boosting, such as through package design or presentation, people might be more likely to put this advice into practice. That could be an interesting avenue of art/science collaboration for future research.

Do you have any experience with using diet to treat mood disorders? Do you think food packaging design and presentation can/should be used to encourage more mental health-conscious decisions? Please comment below.

3 thoughts on “The Gut-Brain Axis and How What We Eat Affects How We Feel

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