Are you thinking with your head? No the other one… your gut.

The next time you can’t control yourself around chocolate, just blame it on the 100 trillion little voices living in your gut.

It’s happened to all of us. All is good and grande in the world, and suddenly and without warning we must have [insert your gluttonous guilty pleasure], and we must have it now! It’s as if someone has planted a devious thought directly in our minds, commanding us to gorge ourselves on everything we know we shouldn’t (goodbye waistline!). Well it turns out we might not be as schizophrenic as I’m making us out to be. There might actually be someone, or rather something(s), causing the cravings. And they just might be planting thoughts in our mind in ways we’re just starting to unravel. Research is demonstrating that we could be eating, tasting, and being emotionally manipulated by decisions arising from a complex ecosystem of roughly 100 trillion little organisms competing in our mini-brain - the gut [1].

“Bacteria within the gut are manipulative”  
Carlo Maley, director of the UCSF Center for Evolution and Cancer [1]

Cocktail party summary:

• Research is finding a direct link between our gut (mini-brain), our brain (the big one… hopefully) and what we are influenced to eat, what we taste, and even our mood.
• Comes from complex interactions between the enormous amount of microorganisms living in our gut (around 100 trillion!), and the signals they send to various locations of the brain.
• Mice studies are showing that these microorganisms are triggering mental cues in their hosts to eat foods that the microorganisms specialize in consuming, even at the detriment of the host [2]. I thought this was a symbiotic relationship?!.
• Basically if the population count of a certain microorganism is high enough in the gut, and let’s say it specializes in eating carbohydrates, it will send signals to the brain saying feed me carbs!
• One good thing is it’s a two-way street. Changing your diet can directly change the number and types of microorganisms, which will influence what you crave.
• I guess you really are what you eat, and vice-versa.

Read on to go deeper down the rabbit hole...

Carlo Maley continues, "There is a diversity of interests represented in the microbiome, some aligned with our own dietary goals, and others not." [1]. Scientists have largely debunked the myth that our food cravings are just our bodies way of telling us which nutrients we need. Using a communication highway (enteric nervous system) that exists between the brain and the gut, microbes have the capacity to change mood and behavior, alter taste receptors, and release chemical rewards and penalties that make us feel good or bad. For example, one randomized, double blind, placebo-controlled clinical human trial found that ingesting a probiotic drink (Lactobacillus casei) significantly reduced anxiety and depression in people suffering from chronic fatigue syndrome [3].

Now that a pathway between the gut and brain has been established, what do we know about the 1.5 kilos (3.3 lbs) of bacteria living in our digestive system? Firstly, not all gut bacteria are created equal. Different bacteria specialize, vary in nutritional needs, and are often in competition with one another. Some like fat, while others prefer sugars, or other macronutrients. But it can go even deeper. For example, there is even a bacteria found in people in Japan that specialize in digesting seaweed. Secondly, we aren't exactly slaves to the little critters, it's more like a two-way street. We can alter our gut microbiome simply by altering our diet. Measurable changes in gut microbiome can be detected just 24 hours after changing (adding or removing) substances from the food we consume. It's a constantly evolving ecosystem.

With all this in mind, let's wrap it up in a nice, compact summary you can divulge to your nerdy best friends.

Dungeons and dragons party summary:

• The gut contains many of the same neurotransmitters as the brain (there are even more neurons in the gut than in the entire spinal cord!)
• The neurons in the walls of the gut form a distributed network called the enteric nervous system.
• When you eat, hormones are secreted in the gut. These hormones can directly activate receptor targets in the brain, but strong evidence points to the vagus nerve playing a large role in gut-brain signaling.
• The vagus nerve acts as an enormous information highway, directly linking over 100 million neurons in the gut directly to the brain.
• Research is pointing to the gut-brain highway as the food craving culprit.
• Using the communication highway between the brain and the gut, microbes can change mood and behavior, alter taste receptors, and release chemical rewards and penalties that make us feel good or bad. A human clinical trial with a probiotic even showed a reduction in anxiety and depression from those suffering from chronic fatigue!
• If you are what you eat, then you have the power to change what you are. The microbiome is constantly evolving based on your dietary intake.

So the next time you stand in front of the fridge asking yourself what you feel like eating, just realize that your decision might have actually come from the loudest of the 100 trillion shouting little voices living in your belly.

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1. https://www.ucsf.edu/news/2014/08/116526/do-gut-bacteria-rule-our-minds
2. "Is eating behavior manipulated by the gastrointestinal microbiota? Evolutionary pressures and potential mechanisms”, DOI 10.1002/bies.201400071
3. Rao, A. V., Bested, A. C., Beaulne, T. M., Katzman, M. A., Iorio, C., Berardi, J. M., & Logan, A. C. (2009). A randomized, double-blind, placebo-controlled pilot study of a probiotic in emotional symptoms of chronic fatigue syndrome. Gut Pathogens, 1, 6. http://doi.org/10.1186/1757-4749-1-6