Hunger: your microbiome's way of saying hello

Hangry

I feel like I am about to starve to death. My stomach has that pain that comes with being hungry and I am struggling to find the foods to say because food is the only food on my food. Food food? food food……food!

{One Pizza later…}

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I’m thinking clearly again, I feel like myself, and I’m curious to know why I got so hungry — to the point of being angry and irritable. I always thought it was because I’m running low on energy and my brain is on a mission to find food, and being hangry keeps people from distracting me on my quest for some tasty tacos or a nice slice of pizza.

As it turns out, the average person has enough energy stored in their muscles, fat, and liver to survive over fifty days without food. If I’m not running on empty, then what is the agonizing, mind altering pain that I call hunger? I did a little (a lot) of research, and I found that being hungry is actually an urge for the feeling of being full, much like an addict has urges for their drug of choice. We are literally addicted to being full, and being hangry is essentially withdrawals from the delicious drug that is food. Except food keeps us alive.

But why does it happen when you don’t actually need to eat every day? What is making me want to eat every few hours when I have enough energy for weeks?

The answer is the brain-gut axis.

The brain-gut axis is a really complex system where the brain and gut communicate with each other through biochemical signals such as neurotransmitters and hormones which travel through the nerves and blood.  These signals help regulate just about everything; feelings of hunger and fullness, blood pressure, the immune system, mood, and more. What is truly fascinating is that one of the major players in the brain-gut-axis are the microbes living in the gut. These microbes play an integral role in producing or regulating many of the hormones and neurotransmitters that are involved in the brain-gut-axis. One way the bacteria does this is by releasing signals that tell Enterochromaffin cells, which line the intestines to produce serotonin: a major neurotransmitter involved in feeling happy, and when it is low results in feelings of anxiety and depression. Interestingly, the enterochromaffin cells produce up to 90% of the serotonin in the body.

Another signal these bacteria produce is called peptide YY (PYY), which can make you feel hungry. Bacteria need food every few hours to keep their metabolism running at full speed. When the bacteria are hungry, they will stop telling our cells to produce serotonin, and will produce PYY that tells the brain it is hungry. When you combine the low serotonin levels with the increased PYY levels you get “hangry”. After eating, the cells stop producing PYY and go back to promoting serotonin production, restoring our mood. These bacteria can even influence what kinds of foods you are craving.

Next time you fail your diet for the seventh time this year, or get angry at someone because you missed lunch, just tell people you need to feed your microbiome.

Further Reading:

Gut/brain axis and the microbiota, http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4362231/#!po=8.91304

Appetite and energy balancing, http://www.sciencedirect.com/science/article/pii/S0031938416301196?via%3Dihub

The Hormonal Control of Food Intake, http://www.sciencedirect.com/science/article/pii/S0092867407004473

The microbiota–gut–brain axis: neurobehavioral correlates, health and sociality, http://journal.frontiersin.org/article/10.3389/fnint.2013.00070/full

 

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