More than 2,000 years ago, a Greek physician, who came to be known as the Father of Medicine, stated, “All disease begins in the gut.” While many traditional medical systems acknowledged the primary role of the gut in overall health, modern research continues to confirm the ancient wisdom of Hippocrates and Western medical systems are now placing a larger focus on gut health.
In addition, it has become increasingly clear that many metabolic, autoimmune and cognitive diseases start with gastrointestinal disturbances or imbalances. Therefore, these findings support that optimal health in pets (and people) cannot be achieved without a healthy gut.
The GI tract actually has numerous important roles beyond basic digestion. It hosts trillions of bacteria, fungi and other organisms, houses 70% of the immune system, performs the majority of neurotransmitter production, influences metabolism, contributes to energy homeostasis, mitochondrial function and much more.
All veterinarians certainly recognize that chronic inflammation of the gut and IBD (Inflammatory Bowel Disease)-related disorders are a rapidly growing health issue for dogs and cats. However, it may not be commonly recognized that chronic GI issues are often associated with a myriad of other health conditions in our veterinary patients, such as allergies, chronic skin conditions, autoimmune diseases, cancers, neurologic and cognitive diseases, and even chronic inflammatory joint disease.
Furthermore, the absence of GI symptoms does not necessarily equate to a healthy gut. Total gut health takes into account the diversity and balance of the gut microbiome and the integrity of the gut barrier amongst other factors. Dysbiosis and intestinal hyper-permeability (i.e., leaky gut) are incredibly common and may not present with obvious symptoms.
Leaky gut occurs as a result of inflammation in the gut lining which leads to separations in the cellular tight junctions of the gut barrier. Once the gut barrier is compromised, it allows for the penetration and absorption of unwanted particles, toxins and pathogenic microorganisms to get into systemic circulation, which can lead to massive immune system disruption and inflammatory changes affecting any or all organ systems. Simply said, a leaky gut puts pets at a higher risk for food sensitivities, allergies, chronic skin disease, autoimmune conditions and metabolic disorders.
Furthermore, it is well understood that a healthy gut barrier is critically important for optimal immune function, as this barrier also protects the GALT (Gut Associated Lymphatic Tissue) which comprises 60-70% of the immune system and creates up to 80% of antibodies.
Chronic inflammation in the gut and subsequent hyper-permeability of the gut lining is also associated with a disturbance in gut microbe populations. A healthy microbiome consists of vast communities of beneficial bacteria, fungi and viruses. Rather than just casual colonizers, these microbe populations make essential nutrients, provide immunological signaling, perform detoxifying functions and influence neurotransmitters and hormones, and even metabolism.
Veterinarians are very familiar with the obesity rates in our canine and feline patients, and the health risks associated with this common health issue. And while there are many casual factors involved here, there is quite a bit of interesting research demonstrating a clear association between obesity or body weight issues with the microbiome populations in both mice and people.
It is also clear that many neurotransmitter chemicals and hormones used by the brain and nervous system such as serotonin, dopamine and GABA are produced in the gut. Serotonin impacts mood and anxiety, and has actually been termed the “happy chemical” because it contributes to happiness and wellbeing. And, conversely, low levels of serotonin have been associated with depression. It is estimated that 70% of serotonin is made in the gut. Dopamine is involved in motor function, mood, decision making and control of other hormones as well. Reports estimate about 50% of dopamine is produced in the gastrointestinal tract by enteric neurons and intestinal cells. GABA regulates stress, anxiety and sleep patterns, and is known to be modulated by bacteria in the gut microbiome. Indeed, bacteria in the gut actually communicate with the brain and the connection between the gut and brain is called the Gut-Brain Axis.
New research may have us looking more at gut health in addressing behavioral disorders of pets as well. A recent groundbreaking study at the University of Oregon has shown a clear link between aggressive behavior of dogs and the microbes that live in the dog’s gut. This study analyzed a population of similar-breed dogs in a shelter setting and compared evaluations of behavior with microbiome status, via testing a series of their fecal samples. While this study could not distinguish the exact relationship between cause and effect, it reveals that the gut microbiome may contribute to aggression or its severity, and that manipulation of the microbiome, via probiotics or dietary changes, may modify behavior. Furthermore, the results of this study suggest that analyzing the canine gut microbiome may have some predictive value in diagnosis of canine behavioral disorders.
With a deeper understanding of the diverse actions of the gut and the critical role it plays in systemic health, metabolism, immune function, behavior status and overall wellbeing, it becomes clear that supporting a healthy gut environment is a powerful proactive approach in maintaining the health of our veterinary patients. +