You are what you eat

Anyone who’s ever tried to cure the blues with Ben and Jerry’s knows that there is a link between our stomachs and our moods. Foods high in fat and sugar release pleasure chemicals like dopamine and opioids into our brains in much the same way that drugs do, and I’d certainly argue that french fries and a chocolate milkshake can perk up even the lousiest of days.

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 included 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.

Now, recent research from a team of doctors at UCLA’s School of Medicine and *CONFLICT OF INTEREST ALERT* funded by Danone, the yogurt company, has for the first time provided support for this brain-stomach connection in humans. These researchers looked at the effect eating yogurt (or as they like to call it, a “fermented milk product with probiotic”) every day for four weeks had on neural responses to pictures of negative faces. This type of task usually causes an increase in activity in emotion and somatosensory regions of the brain, like the amygdala and the insula, indicating an unpleasant or stressful reaction to the images. Compared to control individuals who had eaten just a normal fermented milk product, those who had eaten the probiotics had decreased activity in these brain areas, suggesting they were not as affected by the pictures.

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 affect 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!

 

Dana Smith

PhD student in Experimental Psychology at the University of Cambridge