Anxiety, Stress and the Gut

How many of us have undergone an extreme stress, and described it as feeling like "a pit who among us has not in the stomach?" Who among us has not gone through a "gut wrenching experience?" And readers of my columns and other health writings have likely come across the idea before that "the gut is a second brain".

Now exciting new research has been building, to show the extent to which those common phrases have some truth. A number of recent studies have supported the idea that the digestive tract, and in particularly the billions of bacteria that lined the digestive tract, play and critical role in our emotional health as well as our digestive health.

In one study performed at Michael G DeGroote School of Medicine at McMaster University on mice, the mice were given antibiotics to wipe out the bacteria of the digestive tract. The mice immediately became less anxious and less cautious. This was accompanied by an increase in a fascinating protein called brain derived neurotrophic factor or BDNF. BDNF has been found to be associated with more calmness and less anxiety in the brain. When the antibiotics were continued and the bacteria improved, the mice became anxious again, their normal state. Then they took mice that were passive in nature and treated them so that they were free of bacteria in the gut, and then colonized them with bacteria from mice that were more daring and active. The mice that were colonized immediately became braver and more active. When they took mice that were naturally more active and colonize them with bacteria from passive mice, the colonized mice became more passive.

In another study of mice (apparently, anxiety is a big problem in mice) scientists at the elementary pharmacy by Alexander at University College Cork in Ireland mice were fed a strain of Lactobacillus rhamnosis, a screen similar to typing dose founding many yogurts on the market. The mice, along with a control group of mice were fed bacteria free food, and put through a number of tests to distress them. The bacteria fed mice were much less anxious, ventured much farther into open spaces, and did not give up as easily as the bacteria free mice did. What was doubly interesting about this study was that they looked at brain chemistry of the mice, and the bacteria fed mice had half the amount of corticosteroid, a stress hormone, than the control mice. They also had a change in brain receptors for the neurotransmitter GABA, which is known to relax the brain.

In another mouse study, using a strain of mice that are prone to show more anxious behavior, two strains of the intestinal bacteria Bifidobacterium fed to the mice were actually more effective than the antidepressant SSRI drug, escitalopram (Lexapro)!

So now that we know that bacteria make mice less anxious, what about humans?  A 2013 study at UCLA looked at this using 36 women were divided into three groups, one needing a mixed probiotic yogurt, one eating a dairy product that did not contain bacteria but look the same and tasted the same as yogurt, and the third without any dairy products. Using functional MRIs before and after, the women were then shown pictures of faces and angry or frightened poses. Normally, this would trigger increase activity in certain areas of the brain devoted to emotions. In particular, people who are naturally anxious react highly to this type of stimulus. But the women who ate the probiotic yogurt had a more "mellow" response, showing the intricate relationship between intestinal bacteria and the tendency to anxiety.

But bacteria in the intestine does not tell the whole story. As I'm fond of saying to patients, putting acidophilus and other bacteria in the intestines without preparing the intestines is like throwing seeds onto a parched earth it's also necessary to feed the lining of the gut so that bacteria can colonize easily. And those substances which feed the lining of the intestinal tract are collectively known as prebiotics. Prebiotics, technically, are dietary fibers and oligosaccharide molecules that feed the good bacteria in the intestine, allowing them to multiply and be healthy. The more prebiotics available, the more number and range of good bacteria in the intestine. And so, it makes sense that prebiotic's would also be important in regulating emotions, including anxiety.

In a recent study, 45 healthy adults were giving either prebiotics or a placebo daily for three weeks. The subjects who took the prebiotic showed less anxiety when exposed to negative stimuli, similar to subjects who would've been given anti-anxiety medications. In addition, the prebiotics group had decreases in serum cortisol, the stress hormone, a finding similar to the stressed mice and the earlier study. 

Although that’s the only human study of anxiety and prebiotics so far, our anxious mice have been studied several times to elucidate the relationship between the two.  In one study Brain Behav Immun. 2015 November; 50: 166–177.  mice were fed regular food or food augmented by two milk-derived prebiotics, 3’sialyllactose and 6’sialyllactose.  Multiple tests looking at anxiety behavior, biochemical changes in the lining of the gut and the type of intestinal bacteria, and resilience in the face of stresses showed the powerful effects of prebiotics when given before the exposure to external stresses.

More and more, science is catching up with the simplest of natural health principles, that “you are what you eat.”   And in labs throughout the world,  what is being called the “gut-brain axis” is being validated.  Perhaps soon, people will be taking “yogurt breaks” as a way of destressing during the workday!