The Gut-Brain Connection

Obesity and its connections to a multitude of diseases – diabetes, cardiovascular, hypertension, orthopedic issues and a host of others – are well established. Somewhat less frequently discussed during visits with patients, if mentioned at all, is the possible impact of adiposity – or obesity – on brain function.

An increasing body of literature looks at the gut-brain connection. More specifically, the connection between adiposity and dementia, in particular Alzheimer’s disease, continues to develop, providing support for a link between gut microbiota, neurodevelopment and neurodegeneration. This area of research strongly indicates that intestinal microbiota affects not only brain development, but also its function and regulation of behavior.

Recent research also offers insights into other previously unknown connections between obesity and brain function. A group of New York researchers claim to be the first to have identified a mechanism that, when activated, can reduce food intake. Animal behavior indicates that the sight and smell of food instigates the decision to eat. However, these researchers identified a receptor (hD2R) in the hippocampus that suggests that this part of the brain, which regulates emotions and learning, can also regulate eating.

Another study found a reciprocal relationship between the prefrontal cortex and obesity. The authors posit that variations in the prefrontal cortical structure may predispose some individuals to overconsumption of calorie-dense foods, while at the same time obesity might cause changes to cortical structure and functionality. Studies with mice have found evidence of a different reciprocal relationship. That is, separation form their mothers induces stress, which results in a notable difference in intestinal microbiota; likewise, intestinal microbiome influence depressive behaviors.

This link to depression is similar in humans, with one study finding that among patients with gastrointestinal symptoms, 20 percent report associations with depression. Continued research in this area can help us to understand the causes and biomarkers that influence depression, which can help target potential dietary interventions to improve the efficacy of antidepressants.

As the fattiest organ in the body there is a certain irony to the gut-brain connection. This continues to be an important area of emerging research to provide a clearer understanding how the function of these organs influence each other. Greater knowledge of the biological foundation for diseases such as depression and Alzheimer’s can create a path to potential new ways of therapeutic development.