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How Your Gut Bacteria Influence What You Eat

Your gut is a battleground for microbiota manipulating your brain into eating their favorite foods.
Composite of gut flora. Image: Fruzsina Eördögh

You can't always trust your gut: it may be deliberately lying to you as part of the eternal microscopic war going on inside your body.

Within the human digestive system lives a massive ecosystem of bacteria, known as gut flora or the gut microbiota, and recent research suggests that these microbes can manipulate your brain into eating unhealthy things and even into feeling stressed and depressed. This is all part of the schemes bacteria use to optimize their environment for themselves.


In a recent meta-analysis published in the journal BioEssays, researchers from UC San Francisco, Arizona State University, and the University of New Mexico concluded that these microbiota can influence their host's eating patterns through the vagus nerve. The vagus nerve is a nerve that extends from the brain to the gut, and microbiota love playing with it.

"Microbes have the capacity to manipulate behavior and mood through altering the neural signals in the vagus nerve, changing taste receptors, producing toxins to make us feel bad, and releasing chemical rewards to make us feel good," said senior author Athena Aktipis in a statement. The researchers behind the current study looked at 120 different papers and research articles on gut flora published between 1981 and 2013 to come to their conclusions.

Microbiota have "hijacked the nervous system" with "dramatic effects on behavior," reads the new study. Besides hooking up with the vagus nerve, the gut is also connected to the endocrine system and the immune system, which means these microbiota can also influence those systems, but researchers are unsure of exactly how.

To give you an idea as to how they can overpower and trick your body, remember that microbiota cells outnumber human cells 100 to one in your gut (though they're much, much smaller). These manipulative bacteria can make their hosts crave unhealthy foods rich in sugar and fat and are therefore thought to contribute to obesity. As if that wasn't bad enough, it turns out some of our gut flora is linked to the growth of tumors and may be responsible for some stomach cancers, and possibly other types of cancer.


Image: graphic from the research paper

Gut flora manipulate their host's eating patterns in order to survive and propagate, but also to wipe out their microbial competitors next-door. The gut is a battleground for these bacteria, and manipulating a host's brain into eating certain foods is their primary weapon. Sometimes they'll even endanger the host by making them eat harmful foods. Research has found that people whose gut flora weren't particularly diverse—meaning one bacteria managed to kill off the other types through brain manipulation—were more likely to be obese.

The paper stresses that gut flora is not solely responsible for obesity, though it did find some research to suggest microbiota might be contagious, including the bacteria that causes overeating.

So why shouldn't we nuke these bacteria in our gut with a bunch of antibiotics right away? Well, these microbiota perform important functions like "nutrient harvesting and immune development," the paper explains, i.e. they serve us vitamins and minerals and build up our immune systems in return for living inside us. These microbiota also help the host digest certain foods. People in Japan have a special type of bacteria that helps them digest seaweed, and children in Africa whose diet includes consuming sorghum, a grass, have bacteria that helps them digest cellulose.

But fortunately, everyone's microbiome is easy to manipulate via relatively simple changes in eating habits.

If you're worried about your microbiota composition, know that changing it through diet can take anywhere from a couple of minutes, which is how often the microbiota in your gut evolve, to 24 hours, which is how long it takes the gut flora to restructure itself once dietary changes have taken place. Changing the bacteria in your gut can potentially help change your eating habits, and vice versa.

"Because microbiota are easily manipulatable by prebiotics, probiotics, antibiotics, fecal transplants, and dietary changes, altering our microbiota offers a tractable approach to otherwise intractable problems of obesity and unhealthy eating," wrote the authors in a statement.

In addition to healthier living, "[t]argeting the microbiome could open up possibilities for preventing a variety of disease from obesity and diabetes to cancers of the gastro-intestinal tract" said Aktipis. "We are only beginning to scratch the surface of the importance of the microbiome for human health."