August 18, 2014
How Do Gut Microbes Rule Our Minds, And Our Cravings?
April Flowers for redOrbit.com - Your Universe Online
Our bodies play host to millions of bacteria. In fact, they outnumber our own cells by about 100-fold. And yet, we hold the notion that we are in charge of our own lives, not the bacteria that has just hitched a ride.
A new study, published in BioEssays, tells a different story. The findings reveal that the bacteria within our bodies may very well be affecting our cravings and our moods to ensure that we eat what they want. The research team — from UC San Francisco, Arizona State University and University of New Mexico — say these bacteria could be driving us to obesity.
The research team performed a review of recent scientific literature, finding that microbes influence human eating behavior and dietary choices, forcing the human host to consume the particular nutrients they grow best on. Different species of bacteria need different nutrients. For example, some prefer fat, while others prefer sugar.
Dr. Athena Aktipis, PhD and co-founder of the Center for Evolution and Cancer with the Helen Diller Family Comprehensive Cancer Center at UCSF, says that bacteria not only have to compete with each other for food and to retain a niche within their ecosystem — aka us — they also have different goals for our actions than we do.
The diverse ecosystem of bacteria within our digestive system is known collectively as the gut microbiome. Our decisions could be influenced by signaling molecules released into our gut by the microbiome. Our gut is linked closely to the immune system, the endocrine system and the nervous system, making our physiologic and behavioral responses susceptible to influence from these signaling molecules.
"Bacteria within the gut are manipulative," said Carlo Maley, PhD, director of the UCSF Center for Evolution and Cancer. "There is a diversity of interests represented in the microbiome, some aligned with our own dietary goals, and others not."
Maley suggests that we are not entirely without recourse. By deliberately choosing and altering what we consume, we can influence the compatibility of the gut microbiome, measurably changing it within 24 hours of diet change.
"Our diets have a huge impact on microbial populations in the gut," Maley said. "It's a whole ecosystem, and it's evolving on the time scale of minutes." An example would be the bacteria found in the human gut biomes in Japan, able to digest seaweed because it is a popular choice in the diet.
The researchers believe that the gut bacteria might be affecting our choices and behaviors by acting through the vagus nerve, which connects 100 million nerve cells from the digestive tract to the base of the brain.
"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 Aktipis, who is currently in the Arizona State University Department of Psychology.
The research team, which included University of New Mexico's Department of Emergency Medicine's Joe Alcock, MD, emphasizes that further research is necessary to fully understand the level of influence our gut bacteria might hold over us. For example, if bacteria that digest seaweed were transplanted into the human gut, would it lead the host to eat more seaweed?
For those seeking to improve their health, the authors say there is encouraging news in how quickly the microbiome can be changed. This change can be affected by food and supplement choices, probiotics and antibiotics. Creating an optimized balance of power among bacterial species in our gut may allow us to lead less obese and healthier lives, overall.
"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," the authors wrote.
Image 2 (below): This image illustrates the relationship between gut bacteria and unhealthy eating. Credit: Courtesy of UC San Francisco