Moody Microbes

How are you feeling right now? Happy or sad? Angry or content? The microbes living inside of you, particularly those in your large intestine, are partially responsible for your state of mind right now.

Bacteria from the genus Lactobacillus, a genus of bacteria often found in the intestine.
A creative commons image. Source.  

Microbes—tiny creatures that aren’t even part of the human body—influence the brain?

Yes, intestinal bacteria, and the food we feed them, play critical roles in how we feel. 

Diagram of the large intestine, where our gut bacteria live,
 A creative commons image. Source: Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436

Here’s how bacteria and diet influence the brain:

Microbes talk to the brain through the immune system. Dendritic cells—immune system cells in gut lining—constantly monitor microbes for misbehavior. If the dendritic cells sense that the intestinal bacteria are acting up, they trigger the release of cytokines—compounds that cause gut inflammation.

Cytokines communicate with the brain in two ways: as hormones and as signals sent via the vagus nerve—a thick nerve connecting the gut to the brain. These hormonal and nervous system signals make the brain reduce energy levels, and increase pain sensitivity. Cytokines can even induce feelings of sadness often felt during a stomach ache or gut infection.

It doesn’t require a full-blown gut infection to induce gut inflammation—simply eating a diet high in animal fat can cause the release of cytokines—and the subsequent mood drop.

Bacteria from the genus Klebsiella, a genus often found living in the gut.
A creative commons image. Source.

Microbes also signal the brain through metabolites—byproducts of microbial digestion. The metabolites microbes produce change based on what food we feed them. Metabolites travel through the bloodstream and act as hormones in the brain to influence our moods.

Bacteria from the genus Lactobacillus, a genus of bacteria often found in the intestine.
A creative commons image. Source.

 Generally, food that is good for humans also is good for our bacteria and causes them to release beneficial metabolites. Some metabolites, like those released after eating whole grains and vegetables, trigger release of serotonin, a neurotransmitter which is linked to improved mood. Fatty, unhealthy food on the other hand is likely to cause gut inflammation and the depressed mood that comes with that condition.

Illustration of a human brain. A public domain image. Source.

Gut microbes are so vital to our emotional state and thought process that scientists are starting to think of the gut, the brain, and the human microbiome as a connected system rather than separate entities. This system is often called the gut/brain/microbiome axis. Next time you are in a good mood remember to thank your intestinal microbes!

Check out a previous post I wrote on microbes, We Need Bacteria, to read about the connection between microbes and food allergies.

Sources.

We Need Bacteria

Food allergies are on the rise. If we can eradicate smallpox, why are people becoming fatally ill when exposed to food that’s supposed to be good for them? Are we forgetting about some vital aspect of human health?

I learned from Dr. Jack Gilbert at the American Museum of Natural History’s Teen SciCafe, that yes we are neglecting an important aspect of human health.

Well, it’s not exactly human health that we’re forgetting about but the health of the millions of microbes that cover our skin and inhabit every organ of our bodies except the brain. Yes, bacteria are everywhere, and yes they are good for us.

Peanut butter toast and milk, standard snack or a potential hazard?

In our society we are taught that bacteria are bad and we must kill them with soap. While this is true about some bacteria, there are many other microbes that we need to survive.

 Dr. Jack Gilbert and his colleagues have studied differences in sterile mice (mice never exposed to any bacteria) and normal mice (teeming with bacteria). They found sterile mice’s organs wouldn’t develop properly, they had no fight or flight response to stressful situations, and these mice had severe food allergies. When these sterile mice were treated with good bacteria, they regained their fight or flight response and became tolerant of foods that once poisoned them.

Bacteria are amazing, they’ve been on earth for 3.8 billion years, far longer than we have. We evolved to live with and depend on bacteria. Each of us have our own unique microbe colony which influences many bodily functions from weight gain, to food tolerance, to mental health.

Okay, now we know there’s a link between bacteria and health, now what do we do?

Can we use our knowledge to help decrease risk of food allergies? According to Dr. Gilbert the answer is yes, but we might have to change the way the medical field functions. The nature of our modern, western, medical field is one-size-fits-all. We want easy treatments that work the same way on everyone. But, everyone has a unique microbe colony. Treatments that work for me based off my microbe colony might not work for you. Now that we can figure out people’s microbiomes and understand what they mean, it might be time to go back to personalized medicine.

Dr. Gilbert and his colleagues have worked with more personalized microbe therapy for children with food allergies by introducing butyrate-producing bacteria to their intestines. The bacteria helped the children to handle trigger foods better and reduced the severity of the children’s reactions, or even ended the reactions all together.

Bacteria aren’t the cure-all but it’s about time they get attention. At the Teen SciCafe hosted by American Museum of Natural History, microbes were put in the spotlight thanks to Dr. Gilbert’s lecture. We also got to try out a new student designed card game called Gutsy all about microbes in the gut. The card game was the perfect way to set the mood for microbe talk. Now I’m very excited about bacteria! Improving microbial health can have big impacts, such as reducing risk of food allergies, but doesn’t have to be complicated, just spending more time outdoors and eating food rich in good bacteria can improve your microbiome. (Sauerkraut anyone?)