The Immune System Inside Your Intestines

Gut Bacteria Inside the Colon
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While trite and overused, the proverbial saying "you are what you eat" has held up to the test of time. Decades of scientific research has confirmed that eating healthy whole foods is the key to good health and long lifespans. On the other hand, junk foods and prepackaged, ultra-processed snacks have been linked to a multitude of diseases and health conditions, including obesity, depression, diabetes, inflammatory bowel disease, heart disease, and cancer. Unfortunately, recent studies investigating how a poor diet impacts the gut has added yet another entry to this long list of disorders -- a weakened immune system.

Throughout human history, the digestive system has evolved to form a mutually beneficial, symbiotic relationship with the diverse ecosystem of bacteria inside the gut. We internalized and integrated these microbes into our own biology, forging a critical role for them in our ability to break down and digest food for energy and nutrition. Given its constant exposure to foreign substances through our diet, perhaps it is no surprise that the microbiome came to play a critical role in helping the immune system identify and defend against potentially harmful invaders.

Gut-Blood Barrier Permeability by Pathogens
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Approximately 70 to 80% of the body's immune cells are present in the gut, where they interact closely with the intestinal microbiota. In the process of breaking down food, the beneficial bacteria in the colon produce metabolites which help the body's immune cells produce antibodies to fight disease. At the same time, the gut biome helps defend the outer layer of the intestine which serves as the last line of defense in the gut-blood barrier. This keeps viruses, bad bacteria, and other pathogens out of the bloodstream, preventing them from traveling to other organs and infecting healthy cells.

Unfortunately, any external factors that reduce the quantity and diversity of bacteria in the gut significantly weaken your immunity over time and put you at risk. While antibiotics, heavy metals, and chemotherapy are perhaps the most worrisome with regard to their depletion of your beneficial gut bacteria, a poor diet can also have a significant negative impact. Diets loaded with fats and sugars but deficient in plant-based fiber can effectively starve out the good bacteria in your colon, allowing an opening for bad actors like C. diff and E. coli to take root and attack your digestive system, including the protective lining of the intestine itself. The resulting vulnerabilities in your gut-blood barrier can be easily exploited by harmful pathogens moving through your digestive tract.

Fortunately, a combination of healthy foods and the probiotics can help replenish your gut with the beneficial bacteria needed to keep your immune system strong. Fortifying your diet with nutrient-dense, fiber-rich foods acts like natural fertilizer for good bacteria to thrive, while preventing bad bacteria from being able to take hold inside your gut.



Paul has been interested in medical research since his first organic chemistry class in college. He was a high school biology teacher for 32 years until retiring to spend more time reading, hiking, and camping with his wife and two dogs.

Email Paul at [email protected].


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