It sounds like science fiction, but it seems that bacteria within us -- which outnumber our own cells about 100-fold -- may very well be affecting both our cravings and moods to get us to eat what they want, and often are driving us toward obesity¹. In an article published this week in the journal BioEssays, researchers from UC San Francisco, Arizona State University and University of New Mexico concluded from a review of the recent scientific literature that microbes influence human eating behavior and dietary choices to favor consumption of the particular nutrients² they grow best on, rather than simply passively living off whatever nutrients we choose to send their way.

 

Bacterial³ species vary in the nutrients they need. Some prefer fat, and others sugar, for instance. But they not only vie with each other for food and to retain a niche⁴ within their ecosystem⁵ -- our digestive tracts⁷ -- they also often have different aims than we do when it comes to our own actions, according to senior author Athena Aktipis, PhD, co-founder of the Center for Evolution and Cancer with the Helen Diller Family Comprehensive Cancer Center at UCSF.

 

While it is unclear exactly how this occurs, the authors believe this diverse community of microbes, collectively known as the gut⁸ microbiome, may influence our decisions by releasing signaling molecules⁹ into our gut. Because the gut is linked to the immune system, the endocrine system（内分泌系统） and the nervous system, those signals could influence our physiologic¹⁰ and behavioral responses.

 

"Bacteria within the gut are manipulative," said Carlo Maley, PhD, director of the UCSF Center for Evolution and Cancer and corresponding author on the paper." "There is a diversity of interests represented in the microbiome, some aligned¹¹ with our own dietary goals, and others not."

 

Fortunately, it's a two-way street. We can influence the compatibility of these microscopic¹², single-celled houseguests by deliberating altering what we ingest, Maley said, with measurable changes in the microbiome 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."

 

There are even specialized¹³ bacteria that digest seaweed, found in humans in Japan, where seaweed is popular in the diet.

 

Research suggests that gut bacteria may be affecting our eating decisions in part by acting¹⁴ through the vagus nerve（迷走神经）, which connects 100 million nerve cells from the digestive tract⁶ to the base of the brain.

 

"Microbes have the capacity to manipulate behavior and mood through altering the neural¹⁵ signals in the vagus nerve, changing taste receptors, producing toxins¹⁶ 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 Psychology¹⁷.

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