Chewing and Mental Health

I recently attended a lecture on neurogenesis that discussed some fascinating research on the link between soft-textured foods and a decrease in the ability of adult brains to generate new cells. It reminded me of a podcast by Katy Bowman that I listened to two years ago, which discussed how chewing can stimulate the growth and maintenance of the hippocampus. It made me wonder: if there is a link between the development of the hippocampus and chewing, could damage to the hippocampus lead to a disinterest in chewing and food, creating a negative feedback loop? Is it possible that the size of the hippocampus can be first reduced and then lead to an eating disorder rather than the other way around? Or maybe it’s both?

Hippocampus

The hippocampus is an integral part of the limbic system, the region of your brain that regulates emotions and conveys sensory relays. It helps form, organize, and store memories; connects memories and emotions with your senses (sound, smell, touch); and helps you distinguish between past and present memories. It is one of the first regions of the brain to be damaged by Alzheimer’s, which may give you a better picture of what functions it regulates.

The hippocampus is also involved in behavior inhibition, including the regulation of eating behaviors. When functioning normally, the hippocampus brings up food-related memories to signal you to eat, which stop once you are full. However, people with damage to their hippocampus may experience these memories even when they aren’t hungry so food is constantly on their mind. In one study, rats with hippocampal damage were unable to tell that they were full and would forget they had just eaten. They would see food, pick it up, eat a little, and then drop it, only to repeat the cycle only a few minutes later. Damage to the hippocampus plays a role in eating disorders and disordered eating.

PTSD and Chronic Stress

When someone experiences trauma or even continuous long-term stress, the hippocampus atrophies and becomes under-active. This makes it less effective at making synaptic connections and consolidating memories, keeping the body and mind in threat reaction mode. This also makes it harder, and even impossible, for PTSD patients to differentiate between past and present experiences or to correctly interpret environmental contexts, causing them to overreact in seemingly unrelated current contexts.

Similarly, researchers have noted a high comorbidity between PTSD and eating disorders. A study conducted by the National Institute of Mental Health found that 24.3% of those with eating disorders suffer from PTSD, and another study found that “74% of 293 women attending residential treatment indicated that they had experienced a significant trauma.” These studies have many hypotheses about why this occurs- that the eating disorder is way to cope with the discomforting emotions and experiences, to keep their mind focused on the eating disorder and not on the traumatic memories, to escape, to punish themselves, etc. The complexity of the disorder means that the neurobiology of anorexia nervosa is still unknown. However, studies have shown that those suffering from the disease showed hippocampal volume reduction, and that alterations in hippocampal function and structure could be the result of reduced caloric intake which compromises the supply of energy to the brain.

Chewing

Wait, so what does this have to do with chewing? Chewing is important for preserving and promoting general health, including hippocampus-dependent cognition. According to this study, “both animal and human studies indicate that mastication influences hippocampal functions through the end product of the hypothalamic-pituitary-adrenal (HPA) axis, glucocorticoid (GC). Epidemiologic studies suggest that masticatory dysfunction in aged individuals, such as that resulting from tooth loss and periodontitis, leads to increases in circulating GCs and eventually inducing various physical and psychological diseases, such as cognitive impairment, cardiovascular disorders, and osteoporosis. Recent studies demonstrated that masticatory stimulation or chewing during stressful conditions suppresses the hyperactivity of the HPA axis via GCs and GC receptors within the hippocampus, and ameliorates chronic stress-induced hippocampus-dependent cognitive deficits.”

I personally have ‘coped’ with my PTSD through an eating disorder. An old roommate of mine joked that I was a ‘functioning anorexic’, and for a long time that was true. I was able to maintain a certain level of health and awareness that kept me off the ‘needs help’ radar of friends and family, but eventually had to seek professional help through a recovery program. When I was listening to the podcast, it made me think about when I was first recovering from anorexia and trying to incorporate more foods into my diet. I microwaved everything- all my veggies were steamed until they were super soft. I loved yogurt, oatmeal, and smoothies. I would eat a bowl of cookie-dough flavored hummus for lunch. In the winter, I got really into making soups. It felt easier to eat these types of spoonable foods. It just slid down and I didn’t have to think about it as much.

And maybe this is what I needed when I first started to recover, but I still have a preference for these soft foods. The good news is that the hippocampus demonstrates “an unusual capacity for neuronal plasticity and regeneration. It has recently been demonstrated that changes in the environment can modulate neurogenesis in the dentate gyrus of the hippocampus, and slow the normal age-related decline in neurogenesis.” In other words, chewing and eating a diet with varied textures has been shown to improve neurogenesis and could reverse some of the damage done to the hippocampus.

While it is not clear whether damage to the hippocampus could lead to a decreased interest in eating, it is clear that chewing can increase the health of your hippocampus, helping to generate new cells. Finding something small and easy I can add into my recovery routine makes me feel hopeful. I hope that you have found this new information as interesting as I have. What are your thoughts?

References:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4466515/

https://www.hindawi.com/journals/bmri/2015/412493/

https://content.iospress.com/articles/nutrition-and-aging/nua0054

http://brainblogger.com/2015/01/24/how-does-post-traumatic-stress-disorder-change-the-brain/

https://psychcentral.com/blog/archives/2015/09/16/the-science-behind-ptsd-symptoms-how-trauma-changes-the-brain/

http://www.strengthofawarrior.org/ptsd-and-the-brain/

https://www.recoveryranch.com/articles/eating-disorders/neurological-differences-cause-eating-disorders/

https://www.eatingdisorderhope.com/information/anorexia/how-malnourishment-affects-the-brain-research-on-anorexia-and-neurobiology

https://www.hindawi.com/journals/np/2016/2426413/

https://www.npr.org/sections/health-shots/2016/12/30/506433671/the-wrong-eating-habits-can-hurt-your-brain-not-just-your-waistline

https://www.eatingdisorderhope.com/treatment-for-eating-disorders/co-occurring-dual-diagnosis/trauma-ptsd