What's in your gut affects what's happening in your brain: a growing field of research

(June 24, 2018)

Brain connection
There is a growing body of evidence that the bacteria in our intestines have much more to do with our health than just digestion. Our brain may not be anywhere near our intestines, but many studies are showing that what we eat can have a huge impact on our mental health. The bacterial environment in our gut starts changing at birth and is affected by many factors including vaginal vs. c-section birth, breastfeeding vs. formula, and how we are introduced to solid foods. More changes take place continuously throughout our lives, but generally, the more diverse our bacteria, the healthier our intestines are. Low bacterial diversity is associated with inflammatory markers which travel systemically to the brain and can cause anxiety, depression, and memory loss.

Further, researchers found evidence that a high-fat diet can encourage the growth of bacteria that aid in the production of metabolites which ultimately disrupt chemical signaling in the brain. Mice that were fed a 60 percent fat diet began exhibiting symptoms of anxiety. Importantly, when the mice were treated with antibiotics designed to kill certain bacteria, these symptoms were reversed.

Our intestinal bacteria can affect the development of other common diseases as well. Parkinson's disease (PD), the second most common neurodegenerative disease, causes a decline in motor function, and a recent study found it may be regulated by gut microbiota. Mice that had fecal transplants from humans with PD started developing symptoms right away, while those that had transplants from healthy humans remained healthy. Researchers are now trying to narrow down which microbes are responsible.

Do probiotics work?
Probiotics are becoming huge money makers for food and supplement companies, but are we just throwing money away trying to improve our gut environment with their products? It turns out there are very few studies that show any benefits for people who are already healthy. First, manufacturers pack capsules full of bacteria that are easy to grow in large quantities, not because they are beneficial to us. Second, assuming some of the bacteria survive the trip through our acidic stomach, they aren't going to greatly influence the overall bacterial composition, as the microbes in our gut would outnumber those in a pill by several magnitudes.

That being said, probiotics have been shown to provide benefits for some patients with specific bowel-related conditions. For example, they can reduce common side effects from antibiotics.They can also help protect preterm infants from a potentially deadly gut disease. Probiotics also may relieve symptoms associated with irritable bowel syndrome (IBS). The problem in these cases is that there is no one probiotic that will help all people since internal ecosystems differ from person to person. Creating custom-made probiotics that will benefit individual patients is the newest challenge for researchers. Read the Scientific American article referenced below for more on the "hype" as well as the potential of probiotics for improved health.

Foods for a healthy gut
If you feel healthy already, is there a way to maintain a healthy bacterial environment in your intestines? Eating the right food can encourage healthy bacteria to flourish and protect us from bad bacteria. Here is a list of 10 healthy foods (in alphabetical order) that promote a healthy gut:
10 Foods for a Healthy Gut
Food Other Benefits
1 Apple Cider Vinegar relieves acid reflux
2 Bananas may help reduce inflammation
3 Beans help with weight loss; feeds good gut bacteria
4 Bone Broth helps heal the intestinal lining
5 Cruciferous Vegetables reduce risk of several cancers
6 Garlic prevents gastrointestinal illnesses
7 Mangoes may help control blood pressure
8 Miso (fermented soy bean paste) prevention of cancer tumors and radiation injury
9 Kimchi (Korean fermented vegetables) may reduce social anxiety
10 Yogurt improves digestion

Sources and Additional Reading:
Effect of probiotics and prebiotics on depression. Clinical Nutrition Journal
Early stress and low bacterial diversity and their effect on depression. From IFL Science: IFL Science
How our gut microbes recover after a round of antibiotics. Summary of a recent Duke University study: ElifeScience Summary
Probiotics can protect bones in older women. From University of Gothenburg: Gu.(Sweden) article on probiotics and skeletons
Do probiotics really work? Scientific American article explains the hype as well as the potential: Scientific American article on probiotics
How to choose a probiotic supplement: https://www.healthline.com/nutrition/best-probiotic-supplement
Possible link between Parkinson's and gut health: https://www.cureparkinsons.org.uk/News/parkinsons-starts-in-gut
Fatty foods can trigger anxiety and depression: https://www.inverse.com/article/46087-microbiome-high-fat-diet-depression