It’s 10 PM and you’re about to head home. Exhausted and frustrated (because all you needed was that one last repeat to work), an idea pops into your head – you need a burrito.

From coordinating our heart rate to our respiration, the brain is constantly at work. Like any well-oiled machine, it requires good maintenance and the right kind of fuel to keep it up and running. Although many associate a nutritious diet with cardiovascular health or body weight, what we eat can also have an impact on our moods and behaviours.

bacteria-106583_1920Composed of trillions of microorganisms, the gut microbiota plays a crucial role in metabolism, vitamin production, and defence against infection. In addition to these, the influences of the gut microbiota on human behaviour have also been garnering attention. According to Dr. Carol Maley, the director of the Center for Evolution and Cancer at the University of California, San Francisco (UCSF), the “bacteria within the gut are manipulative” and have preferences for the types of food that they consume – some fancy sweets while others favour fats (I can identify with this). These preferences in turn affect the way we feel about certain cuisines and may even contribute to why we get cravings for particular foods. Conversely, what we eat can influence the microbial composition in the gut. Following a shift from a plant-based to a meat-based diet, or vice versa, changes in gut microbial populations and bacterial gene expression can be witnessed within a few days’ time; however it remains inconclusive as to how long these changes are sustained.

Just last year, researchers at the Imperial College of London and the University of Glasgow found that ingestion of an inulin-propionate ester supplement could ease cravings for calorically high foods such as cake and pizza. Propionate is a compound produced by bacteria in the gut that digest a type of fiber called inulin. When released, propionate signals to the brain to curb appetite. Following administration of either inulin-propionate ester or inulin alone, volunteers completed an MRI scan while being presented with an assortment of food images. Less activity was found in the areas of the brain associated with reward-signalling in those given the supplement. Some individuals may produce higher levels of propionate naturally and be more resistant to cravings, suggesting the effects that differing gut microbial compositions can have.

Those who consume traditional diets, such as the Mediterranean diet – comprised of whole unprocessed foods and a large consumption of fruits and vegetables – have been associated with lower risks of depression. The typical “Western” diet, on the other hand, which is chock full of refined sugars and processed goods, has been shown to drive inflammation and the production of reactive oxygen species (ROS). Diets rich in healthy carbohydrates have been suggested to promote the conversion of tryptophan to serotonin. Involved in sleep regulation and appetite, serotonin is known as your body’s feel-good neurotransmitter and it is estimated that up to 90% of your body’s serotonin is produced in the gut. This raises another case for the influence of diet and the gut microbiota on mood and behaviour.

Like fingerprints, gut microbiota are unique to every individual. Food and nutrition show great promise in the development of personalized treatments of psychiatric conditions but many questions still remain with regards to the link between microbiota composition and mental health. In the meantime, go and get that burrito.


  1. University of California, San Francisco (UCSF). “Do gut bacteria rule our minds? In an ecosystem within us, microbes evolved to sway food choices.” Science Daily. ScienceDaily, 15 August 2014. <>.
  2. “Do microbes control our mood?.” ScienceDaily. ScienceDaily, 20 October 2016. <>.
  3. Feltman R. “The Gut’s Microbiome Changes Rapidly with Diet.” Scientific American, 14 December 2013. <>.
  4. Byrne C. et al. “Increased colonic propionate reduces anticipatory reward responses in the human striatum to high-energy foods.”Am J Clin Nutri, 11 May 2016. doi: 10.3945/ajcn.115.126706
  5. Selhub E. “Nutritional psychiatry: Your brain on food.” Harvard Health Publications, 16 November 2015.<>.
  6. Rao, T. S. Sathyanarayana et al. “Understanding Nutrition, Depression and Mental Illnesses.” Indian Journal of Psychiatry 50.2 (2008): 77–82. PMC. Web. 2 June 2017.
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Sharon Ling

Sharon is an MSc candidate within the lab of Dr. Rae Yeung in the Department of Immunology at the University of Toronto. Outside of the lab, Sharon enjoys watercolour painting, working out, and grabbing weekly dim-sum with her grandma.

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