One of the most complex body systems is the digestive system. It has so many connections beyond just getting nutrients from food (such as inflammation, immunity etc.) For many of the same reasons you can have “GUT-BRAIN” connections that can affect how the brain functions, how much inflammation it has and many other things.
https://www.ctrnetwork.com/drpaulanderson
Some resources:

FREE article “The Brain on Fire”: https://www.consultdranderson.com/?s=Brain+on+fire

Johns Hopkins news: http://www.hopkinsmedicine.org/health/healthy_aging/healthy_body/the-brain-gut-connection

Gut-Brain and Microbes: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4367209/pdf/AnnGastroenterol-28-203.pdf

Psychology Today review: https://www.psychologytoday.com/blog/evolutionary-psychiatry/201404/the-gut-brain-connection-mental-illness-and-disease

Scientific American: https://www.scientificamerican.com/article/gut-second-brain/