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The gut-brain axis

This is an excerpt from New Power Eating, The by Susan Kleiner & Maggie Greenwood-Robinson.

Your gut (stomach and intestinal tract) and brain are tightly connected and in constant communication with each other in what scientists call the gut-brain axis. The brain talks to the gut, and the gut talks to the brain—bidirectional communication that plays a key role in physical and mental health, according to an accumulating amount of research compiled by scientists.


You have collections of microbes in your body (about a trillion), referred to as microbiota. In total, the microbiota weigh about twice as much as your brain. The brain influences gastrointestinal and immune functions that control the populations of good and bad bacteria in the gut, and these same good and bad bacteria influence the creation and regulation of brain neurotransmitters that affect brain function, mood, and behavior. For example, a study published in 2015 in Biological Psychiatry involved the transfer of gut bacteria from the intestines of obese mice to normal-weight mice. The recipients, whose weight remained unchanged, developed neuropsychological symptoms characteristic of obese mice, such as anxiety and changes in cognition and behavior.


Studies in humans have suggested that introducing certain foods and restricting others can help change the microbiota and reduce levels of anxiety or depression. Many of the dietary changes they suggest—which mirror the new Power Eating recommendations you will find in this book—are generally healthy overall and offer a way to protect and enhance brain health. Overall, these studies suggest that you can positively affect the health and diversity of good gut bacteria by taking the following actions:

  • Avoid a high-fat, processed, and sugary Western-type diet. This appears to boost levels of unhealthy gut bacteria and significantly increases the risk for inflammation and depression.
  • Focus on whole foods. These include plenty of fiber-rich whole grains, fresh fruits and vegetables, fish, and healthy fats such as olive oil, all of which have been linked to the promotion of beneficial gut bacteria.
  • Eat fermented foods. These foods contain probiotics, which are living microorganisms that improve health by adding to the beneficial bacteria in your gut. Research suggests that regularly consuming the probiotics found in fermented foods such as yogurt, sauerkraut, kimchi and pickles, or taking probiotic supplements, may alter the nature of the microbiota in the gut, resulting in the production of compounds that are associated with positive brain changes. An important study published in 2013 in the journal Gastroenterology found that women who ate a cup of yogurt containing probiotics twice a day for one month reacted with less stress and anxiety to images of angry or frightened faces than did similar women who did not eat probiotics.
  • Eat soluble fiber. This naturally contains “prebiotics,” dietary fiber that stimulates the growth and activity of healthy bacteria in your gut. Good sources of prebiotics include whole grains, flaxseed, onions, bananas, and garlic. Among other beneficial effects, preliminary research suggests prebiotics may help you better manage stress. In a study published in 2015 in Psychopharmacology, three weeks of prebiotics consumption significantly suppressed levels of the stress hormone cortisol and shifted volunteers’ thought processes from a negative focus to a more positive focus.
  • Always combine your training with a healthy diet. This is another way to keep your intestinal bacteria in balance. A 2014 study comparing healthy nonathletes with 40 Irish soccer players revealed that the soccer players had about twice as much diversity in their gut microbiota; in other words, a higher ratio of good bacteria to bad bacteria, a sign of good health.