Imagine that you've become very, very small and you're entombed within your gut. You look around you and notice that you are not alone. There are trillions of other very small creatures in here with you. All of these bacteria, viruses and fungi are busy doing very simple tasks. First, they're trying to stay alive as they battle each other for dominance. Second, they're trying to win this continuing battle by replicating themselves as much as possible. In order to do so they require the food that is regularly provided by each meal consumed. Whoever eats more also produces more offspring and wins the battle of survival; this war is waged continuously every day.
Scientists are beginning to understand how a shift in the mixture of these bugs can lead to poor health, including heart disease, inflammatory bowel diseases, high cholesterol, obesity and cancer. The balance of gut bacteria is also thought to influence behavior and the presence of certain mental disorders, such as depression. How does this happen? How can the bugs in your gut convince your brain that you should feel happiness or sadness and anxiety?
A recent study suggests that the answer is related to the mechanism by which alcohol acts in your brain to produce the same types of feelings. According to scientists at McMaster University in Canada and the University of Cork in Ireland [published in the Proceedings of the National Academy of Sciences] the specific mechanism involves a protein that responds to the presence of alcohol in the brain; this protein is called the GABA receptor. The bugs in your gut communicate with your brain via the GABA receptor. I would like to think that the little bugs are telling your brain "thank you" for that last tasty meal.
How does this communication work? Let's imagine that you're feeling stressed due to the events of your life. In response to this stress your body releases lots of stress hormones. When stressed mice were fed a broth containing some Lactobacillus rhamnosus bacteria (this bacterium is commonly found in yogurt and other dairy products) they became significantly less anxious and had lower levels of stress hormones in their blood. The researchers determined that the bacteria were somehow communicating via the vagus nerve. The vagus nerve is a very important neural two-way highway that connects your brain with all of the organs of your body.
Should you eat more yogurt? Possibly. There is still too little information available to prove that this same gut-brain communication process happens similarly in humans. After all, eating too much Lactobacillus rhamnosus can also make you quite sick. In a previous blog about food allergies I explained why you need these bugs to be in harmony with each other and with your human cells. When you induce an imbalance in their numbers by what you chose to eat they may punish you with anxiety or depression. A nice scary thought to consider this Halloween.
© Gary L. Wenk, Ph.D. Author of Your Brain on Food (oxford, 2010)