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The Brain in your Gut

Gut health linked to brain health.

You may already know that different parts of the body communicate and send signals back and forth. Researchers have recently discovered that "cross-talk" between gut bacteria and the brain may reduce your risk for a variety of health issues, including psychiatric illness, intestinal problems and even obesity.

Gut flora is made of the microorganisms (bacteria) that naturally live in our digestive tracts. Gut bacteria (flora) has been linked to diseases like inflammatory bowel disease and even asthma.
According to scientists, stress can alter the natural balance of bacteria in the intestines, leading to a decrease in immune system function. When scientists reduced the number of bacteria in the intestines using antibiotics, some of the effects of stress on the immune system were prevented. This led researchers to discover that stress can not only change the bacteria levels in the gut but also this decrease in bacteria levels and perhaps an increase in more harmful bacteria caused by stress can have a detrimental effect on the immune system.

Other important functions of the gut-brain axis include animal research showing that the colonization of the gut with healthy bacteria right after birth can actually regulate the set point for how we respond to stress and can affect behavior, learning and memory. Colonization occurs in humans by vaginal birth (vs. C-Section) and by breast feeding. Animals without the healthy bacteria right after birth in their gut were more likely to be anxious and were more likely to engage in behaviors deemed risky. Yet, when young bacteria-free mice were exposed to microorganisms they developed more normal behaviors while adult germ-free mice exposed to microorganisms did not experience any behavioral changes. This suggests the normal colonization of flora during infancy influences early brain development.

Other research discovered that there is a difference in gut bacteria in obese people versus the bacteria in their leaner counterparts. Animal studies found that by changing the diets of mice colonized with typical human gut flora were fed a high fat, high sugar diet (Western diet) the mice gained more weight and produced more of the bacteria specifically found in obese individuals than mice who were given low-fat diets. This research is a key component to understanding how microorganisms can potentially influence genetic information related to how the body stores fat. It is not clear whether obesity itself causes the change in gut flora or whether the change in gut flora signals the body to store fat more readily. More research is needed
No matter how you look at it, however, it is more important than ever to pay attention to what is happening in your gut.

K. M. Neufeld, N. Kang, J. Bienenstock, J. A. Foster. Reduced anxiety-like behavior and central neurochemical change in germ-free mice. Neurogastroenterology & Motility, 2011; 23 (3): 255 DOI: 10.1111/j.1365-2982.2010.01620.
Elsevier. "Stress affects the balance of bacteria in the gut and immune response." ScienceDaily22 March 2011. 3 April 2011 <;.

F. Backhed, H. Ding, T. Wang, L.V. Hooper, G.Y. Koh, A. Nagy, C.F. Semenkovich, J.I. Gordon. The gut microbiota as an environmental factor that regulates fat storage. Proc Natl Acad Sci U S A. 2004 November 2; 101(44): 15718-15723.
Published online 2004 October 25. doi:10.1073/pnas.0407076101.,8599,1938023,00.html

More from Carolyn C. Ross M.D., M.P.H.
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