The way people eat -- their food choices, food cravings, even their inability to modify their intake in order to get into better shape -- may all come down to gut reactions, literally.

That isn't to say the way folks consume food is determined by rash decisions. Rather, new research by teams from the University of California San Francisco, Arizona State University and University of New Mexico has concluded the microbes living inside of us all -- in our digestive systems -- may influence our culinary likes and dislikes and eating habits much more than anyone every realized.

The findings of the study, published in the journal BioEssays, suggest gut microbes influence human eating and dietary choices in favor of the particular nutrients that help them grow best, rather than simply passively living off whatever nutrients we choose to send their way.

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

Nevertheless, people can influence the compatibility of these microscopic, single-celled houseguests by altering what they ingest, Maley said, with measurable changes in the microbiome -- the community of microbes that live inside us -- 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."

Bacterial species vary in the nutrients they need, explained the researchers. So, while some organisms prefer fat, others are partial to sugar, for example.

There are even specialized bacteria that digest seaweed, found to a great extent in humans from Japan, where seaweed is popular in the diet.

Additionally, according to the paper's senior author Athena Aktipis, PhD, co-founder of the Center for Evolution and Cancer with the Helen Diller Family Comprehensive Cancer Center at UCSF, the bacteria not only vie with each other for food and to retain a niche within their ecosystem -- which happens to be our digestive tracts -- but often have different aims than we do when it comes to our own actions .

So, while it's still not completely clear how it happens, it seems from the research that the microbes may influence our dietary decisions by releasing signaling molecules into our gut.

And, since the gut is linked to the immune system, the endocrine system and the nervous system, those bacterial messages could be swaying our physiologic and behavioral responses.

"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.

Aktipis -- an evolutionary biologist and a psychologist who says she 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 -- noted the evolution of tumors and of bacterial communities are linked, as some of the bacteria that normally live within us cause stomach cancer and likely 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.