Do gut bacteria rule our minds?

This image illustrates the relationship between gut bacteria and unhealthy eating. Credit: Courtesy of UC San Francisco

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 obesity.

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 nutrients they grow best on, rather than simply passively living off whatever nutrients we choose to send their way.

Bacterial 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 niche within their ecosystem—our digestive tracts—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 microbiome, may influence our decisions by releasing signaling molecules into our gut. Because the gut is linked to the immune system, the endocrine system and the nervous system, those signals could influence our physiologic 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 aligned with our own dietary goals, and others not."

Fortunately, it's a two-way street. We can influence the compatibility of these microscopic, 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 specialized bacteria that digest seaweed, found in humans in Japan, where seaweed is popular in the diet.

Research suggests that may be affecting our eating decisions in part by acting through the vagus nerve, which connects 100 million 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.

In mice, certain strains of bacteria increase anxious behavior. In humans, one clinical trial found that drinking a probiotic containing Lactobacillus casei improved mood in those who were feeling the lowest.

Maley, Aktipis and first author Joe Alcock, MD, from the Department of Emergency Medicine at the University of New Mexico, proposed further research to test the sway microbes hold over us. For example, would transplantation into the gut of the bacteria requiring a nutrient from seaweed lead the human host to eat more seaweed?

The speed with which the microbiome can change may be encouraging to those who seek to improve health by altering microbial populations. This may be accomplished through food and supplement choices, by ingesting specific in the form of probiotics, or by killing targeted species with antibiotics. Optimizing the balance of power among bacterial species in our gut might allow us to lead less obese and healthier lives, according to the authors.

"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.

The authors met and first discussed the ideas in the BioEssays paper at a summer school conference on evolutionary medicine two years ago. Aktipis, who is an evolutionary biologist and a psychologist, was drawn to the opportunity to investigate the complex interaction of the different fitness interests of microbes and their hosts and how those play out in our daily lives. Maley, a computer scientist and evolutionary biologist, had established a career studying how tumor cells arise from normal cells and evolve over time through natural selection within the body as cancer progresses.

In fact, the evolution of tumors and of bacterial communities are linked, points out Aktipis, who said some of the bacteria that normally live within us cause stomach cancer and perhaps other cancers.

"Targeting the microbiome could open up possibilities for preventing a variety of disease from obesity and diabetes to cancers of the gastro-intestinal tract. We are only beginning to scratch the surface of the importance of the microbiome for human health," she said.

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User comments

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antigoracle
1 / 5 (9) Aug 15, 2014
I call bollocks
verkle
1 / 5 (9) Aug 15, 2014
It is so interesting to see how people love to come up with yet another excuse for our own lusts and evil desires. Now, blame your obesity on the bacteria! What a shame on science. We can try to blame genes, bacteria, our growing-up experiences, society, religion, etc, etc for all of our faults and shortcomings. This makes us feel better---because then it is not our fault, but someone (or something) else's fault.

This has been happening since the beginning of the world.

anonymous_9001
5 / 5 (12) Aug 15, 2014
This has been happening since the beginning of the world.


Which was not 6000 years ago.
yep
5 / 5 (8) Aug 15, 2014
Think with your gut, that's not bollocks.
Even sexual attraction could be in some way regulated by our microbiota.
http://www.the-sc...Gut-sex/
How much of our ego is that five pounds of other in us?
alfie_null
5 / 5 (8) Aug 16, 2014
. . . This makes us feel better---because then it is not our fault, but someone (or something) else's fault.

Would it make you feel better if all obese people were to own up to their evil lustful ways? I hardly have to say that's a remarkably shallow (and perverse) view.

When you see a morbidly obese person, is your thought "there goes a minion of Satan"?
PPihkala
5 / 5 (8) Aug 16, 2014
"We are only beginning to scratch the surface of the importance of the microbiome for human health," she said.

I think this is an understatement.
thingumbobesquire
3.3 / 5 (4) Aug 16, 2014
The analogy to society of these bugs in the gut are the parasitical "royal" families looting the planet.
antigoracle
1.2 / 5 (6) Aug 16, 2014
Think with your gut, that's not bollocks.

Nope. That's when y'er George Dubya.
So, bacteria ran the US for 2 terms.
russell_russell
4.6 / 5 (5) Aug 16, 2014
The cell numbers are:
Outnumbered ten to one.

I am going to cooperate and be a good host.
It takes too much effort not to host. Sterile life excludes adaptability.
JVK
1.9 / 5 (9) Aug 16, 2014
Re: "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."

Nutrient-dependent pheromone-controlled ecological adaptations: from atoms to ecosystems
http://figshare.c...s/994281

"This atoms to ecosystems model of ecological adaptations links nutrient-dependent epigenetic effects on base pairs and amino acid substitutions to pheromone-controlled changes in the microRNA / messenger RNA balance and chromosomal rearrangements. The nutrient-dependent pheromone-controlled changes are required for the thermodynamic regulation of intracellular signaling, which enables biophysically constrained nutrient-dependent protein folding; experience-dependent receptor-mediated behaviors, and organism-level thermoregulation in ever-changing ecological niches and social niches."
JVK
1 / 5 (7) Aug 16, 2014
Which was not 6000 years ago.


Analysis of 6,515 exomes reveals the recent origin of most human protein-coding variants
http://dx.doi.org...ure11690

"We estimate that approximately 73% of all protein-coding SNVs and approximately 86% of SNVs predicted to be deleterious arose in the past 5,000–10,000 years."

This suggests beneficial variants also arose via nutrient-dependent amino acid substitutions that stabilized the DNA in organized genomes of modern human populations. That stability enables ecological adaptations to ecological variation that would otherwise mutate a species into extinction, not cause them to become another species over millions of years.

Thus, claims
This has been happening since the beginning of the world.
appear to be consistent with claims of a 6-10,000 year-old Earth and nutrient-dependent pheromone-controlled ecological adaptations perturbed by mutations associated with nutrient stress and social stress. There's a Book about that!
JVK
1 / 5 (8) Aug 16, 2014
Kohl's Laws of Biology

Life is nutrient-dependent. That is a Biological Law. The ecological origin of all biological laws is apparent 1) in the context of systems biology [91]; 2) in the context of the metabolism of nutrients by microbes [157]; and 3) in the context of how the metabolism of nutrients results in species-specific pheromones that control the physiology of reproduction [158]. Taken together, the systems biology of nutrient metabolism to species-specific pheromones, which control the physiology of reproduction, can be expressed in a summary of Kohl's Laws of Biology: 1) Life is nutrient-dependent. See for review [2, 31]. The physiology of reproduction is pheromone-controlled. See for review [30]. In the context of nutrient-dependent epigenetically-effected human reproduction, it is clearer that the epigenetic effects of human pheromones integrate neuroendocrinology and behavior [104], which includes the neuroendocrinology of mammalian behavior..."
Smithder
5 / 5 (4) Aug 17, 2014
Look first at Candida. It eats carbo, and when humans get overloaded with candida, they develop carbo cravings. This becomes a nasty spiral into eating more and more carbo and sugar as candida takes over our gut, causing depression, IBS and a hoard of related conditions.

This article rings scary true.
animah
5 / 5 (4) Aug 17, 2014
Keep going scammer James V Kohl. Your SEO profile is slowly changing, and it won't stop until you stop spamming this board:

https://www.googl...+scammer
Grallen
not rated yet Aug 19, 2014
I've kind of looked at multi-cellular life as tools of bacteria v bacteria warfare. :P
PhotonX
5 / 5 (3) Aug 20, 2014
It is so interesting to see how people love to come up with yet another excuse for our own lusts and evil desires. Now, blame your obesity on the bacteria! What a shame on science.
That's rich coming from someone who thinks our problems began with a talking snake persuading a naked woman to eat an apple.
JVK
1 / 5 (3) Aug 20, 2014
Diversity and function of the avian gut microbiota http://dx.doi.org...2-0645-z links what's known about nutrient-dependent pheromone-controlled transgenerational epigenetic inheritance from yeasts http://rspb.royal...abstract to nematodes http://www.cell.c...)00806-X and to ecological speciation via conserved molecular mechanisms the eliminate any further consideration of mutation-initiated natural selection and the evolution of biodiversity. See for examples from other model organisms: http://www.ncbi.n...24693353
Smithder
5 / 5 (1) Aug 20, 2014
That's rich coming from someone who thinks our problems began with a talking snake persuading a naked woman to eat an apple.


I think you are bing a little too critical - my talking snake once persuaded a naked woman to eat my apple and I ended up in all manner of trouble...