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Ketogenic Diet and Mental Illness: Introduction to the Gut-Brain Connection

The ketogenic diet has been researched for its health benefits for nearly 100 years (Bostock, Kirkby, & Taylor, 2017). In the 1920s, it was utilized as a treatment option for epilepsy (Wheless JW, 2008). Recently, it has become more researched as a potential treatment option for mental illness. Promising studies have shown the benefit of ketogenic diet for illnesses such as autism spectrum disorder, depression, ADHD, bipolar disorder, and anxiety (Bostock, Kirkby, & Taylor, 2017).

To better understand the mechanism of action that ketogenic diet exhibits on the body, we need to understand the gut-brain connection. The ketogenic diet is fascinating as it upends the whole process of bad bacteria proliferating. Several studies have shown that a ketogenic diet decreases the bad bacteria in the gut and helps restore the good bacteria (Paoli et al, 2019). The intestines and the gut are not disconnected or different entities within the body; rather, the brain innervates with the gut via the vagus nerve. The sympathetic part of the autonomic nervous system and the hypothalamus-pituitary-adrenal axis (HPA) co-modulate the secretion, motility, and blood flow affecting intestinal permeability and influencing various GI disorders (Skonieczna-Zydecka, Marlics, Misera, Koulaouzidis, and Loniewski, 2018). The central nervous system is the brain and spine. The autonomic nervous system is an extension to the central nervous system and manages body functions that we cannot consciously control, such as heartbeat, breathing, and digestive processes. The sympathetic nervous system is an extension to the autonomic nervous system and controls the fight-or-flight response, causing things like increased heart rate, pupil dilation, expansion of airway and lungs. Heaney (2013) states, “The hypothalamic-pituitary-adrenal axis (HPA axis) is an interactive neuroendocrine unit comprising of the hypothalamus, the pituitary gland, and the adrenal glands. The hypothalamus is located in the brain and the pituitary at the base of it, whereas the adrenals are on top of the kidneys. The HPA axis plays key roles in basal homeostasis and in the body’s response to stress.” Basically, the central nervous system works with the gut through a network of neural and hormonal pathways to maintain balance within the body (Skonieczna-Zydecka et al, 2018).

Through this network, normal body functions are carried out. The intestines have bacteria (both good and bad) that inhabit the region. These bacteria carry out critical tasks that our bodies rely on, such as making vitamin K and b12 and synthesizing gamma aminobutyric acid (GABA) and serotonin (Paoli et al, 2019). Vitamin b12 is important for nerve tissue health, brain function, and red blood cell production. Vitamin K is important for helping the blood to clot. Serotonin is important for mood and helps regulate feelings of happiness, and anxiety. GABA will be discussed further in this post. These by-products of the bacteria work with the enteric (gut) nervous system and the vagus nerve (Paoli, et al, 2019). However, when harmful gut bacteria begin to proliferate, this process destabilizes the operation of the gut-brain connection, thereby creating an environment conducive for illness. Bad gut bacteria can be caused from a number of things; however, what often impacts the gut the most is what is at the end of one’s fork.

So how does the ketogenic diet impact mental health? The ketogenic diet affects the production of GABA, an inhibitory neurotransmitter. That means it helps slow things down within the brain: think of it as the brake pedal in the brain. This neurotransmitter helps with anxiety and rumination of thoughts. It has now been demonstrated that GABA is produced by different strains of lactobacilli and bifidobacteria (Paoli et al, 2019). If the body does not have adequate good bacteria, or there is an imbalance (dysbiosis), GABA may not be made in proper quantities to meet the body’s demand, thereby resulting in varying forms of mental illness. When eating a ketogenic diet, the good bacteria that produce GABA are restored, thereby increasing the levels within the body and reducing or alleviating mental symptoms.

(Credit to Paoli et al, 2019)

Above is an explanatory chart about how the ketogenic diet interacts with not only the gut, but also the brain. As you can see, changing one’s diet helps to restore balance within the gut. When a ketogenic diet is first initiated, the body’s gut bacteria will decrease. This is because the body begins starving out the bad bacteria, thereby reducing the amount in the gut. However, research shows that over time, the bacteria will level out and return to a normal state (Paoli et al, 2019).

There are many of resources available about the ketogenic diet. However, consuming appropriate and healthy levels of fats, proteins and low carbohydrates is the key to a successful nutrition plan. Avoiding artificial sweeteners is important as well-several studies have shown that artificial sweeteners cause a negative impact on overall gut health and bacteria and may in fact increase one’s risk of developing cardiometabolic diseases (Paoli et al, 2019). Eating fermented and cultured foods also has a positive benefit to the gut. According to Paoli et al (2019), “It has been reported that foods enriched with these microorganisms are able to recovery and improve gut microbiota, reaching the state of eubiosis. Cultured-milk products (kefir, Greek yogurt), traditional buttermilk, water kefir, fermented cheese, sauerkraut, kimchi, miso, kombucha and pickles contain several and different “friendly bacteria” such as Lactobacillus acidophilus, Lactobacillus delbrueckii subsp. bulgarius, Lactobacillus reuteri, Saccharomyces boulardii and Bifidobacterium bifidum.” (When the author says “eubiosis”, that means beneficial gut bacteria.)

In conclusion, the ketogenic diet has very promising results and may be used as a treatment for mental illness in either the presence or absence of medications. As always, it is important to talk to your healthcare provider to ensure safety in medication management and monitoring lab work.


Bostock, E. C. S., Kirkby, K. C., & Taylor, B. V. M. (2017, March 20). The Current Status of the Ketogenic Diet in Psychiatry. Retrieved April 21, 2020, from

Heaney J. (2013) Hypothalamic-Pituitary-Adrenal Axis. In: Gellman M.D., Turner J.R. (eds) Encyclopedia of Behavioral Medicine. Springer, New York, NY

Paoli, A., Mancin, L., Bianco, A., Thomas, E., Mota, J. F., & Piccini, F. (2019, July 15). Ketogenic Diet and Microbiota: Friends or Enemies? Retrieved April 21, 2020, from

Skonieczna-Żydecka, K., Marlicz, W., Misera, A., Koulaouzidis, A., & Łoniewski, I. (2018, December 7). Microbiome-The Missing Link in the Gut-Brain Axis: Focus on Its Role in Gastrointestinal and Mental Health. Retrieved April 21, 2020, from

Wheless, J. W. (2008, November 30). History of the ketogenic diet. Retrieved April 21, 2020, from

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