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This brain-belly connection works in the opposite direction, too. Ever felt nauseous before giving a big presentation? Or had butterflies in your stomach on a first date? It's this system relating feedback from your brain to your gut causing those sensations and giving you physical signals that something big is about to happen.
However, instead of trying to suppress those feelings (or running to the bathroom every five minutes) it now appears that we can use this brain-body loop to our advantage. Formally referred to as the microbiome-gut-brain axis, bacteria that live in our stomach and intestines can affect our responses to stress and anxiety, and research in recent years has shown that probiotic bacteria - like those found in many strains of yogurt - can help to reduce anxiety and elevate mood in addition to helping us "stay regular".
Previous research has shown reduced fear and stress responses during anxiety-inducing tests in mice who were fed broth with an added probiotic. This includes less freezing in the face of fear, greater exploration of new environments, and fewer indicators of depression during a behavioral despair test (cheerful, huh?). These chilled out mice also had lower levels of corticosterone - a major stress hormone - after being tested, corroborating these behavioral findings.
Curiously though, there was no difference between the groups in probiotic levels found in stool samples taken (yes, they tested their poop), and none of the participants reported feeling any changes in their levels of stress, anxiety or depression during the study. However, there were significant differences in brain activity between the groups while they were resting, including in the areas identified during the task. Altogether, it looks like even small amounts of probiotics (i.e., not enough to change your gut levels) can still have a significant effect on our brain activity, even without noticeably changing our moods.
This interaction between our guts and our gray matter is thought to be facilitated by the vagus nerve traveling down the base of the brain into the stomach, transmitting sensory information and chemical signals from internal organs back up to the brain. Supporting this theory, when this nerve was cut in the first study the positive effects of the probiotics disappeared, and the test mice were back to their normally anxious selves.
It doesn't appear that non-fermented milk products have the same positive effects on the brain, so it looks like I'll be switching my usual Ben and Jerry's to frozen yogurt for the next few weeks while I finish writing up my PhD thesis. Maybe it'll help with my growing "thes-ass" too!
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Bravo, JA et al. Ingestion of Lactobacillus strain regulates emotinoal behavior and central GABA receptor expression in a mouse via the vagus nerve. Proceedings of the National Academy of Sciences 108: 16050-16055 (2011).
Tillisch, K et al. Consumption of fermented milk product with probiotic modulates brain activity. Gastroenterology 1401: 1394-1401 (2013).
Image credit: D.Mallory (via Flickr) and Gray, H. Accessed online via Bartleby. Anatomy of the Human Body (1918). This image is in the public domain because its copyright has expired.
http://healthland.time.com/2012/04/24/healthy-foods-that-really-arent-nutritionists-weigh-in/slide/frozen-yogurt/
Great question! A quick google search shows that some frozen yogurt chains (Red Mango is listed as one) are investing in more stable probiotic strains in an attempt to keep them intact through the freezing process. But in general I think you're right, and you'd be hard pressed to find a link between froyo consumption and noticeable probiotic-related health benefits (which is still a pretty shaky claim to begin with). Guess I should change my diet strategy!
I was wondering how your self-experimentation is going and if you are having positive results from eating probiotics. My question for you is this: Would you actually get the same benefits from frozen yogurt as you would from refrigerated yogurt? Since many of the probiotics are thermophiles, I wonder if they survive the freezing process?
Thanks for the article.
Jenny