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Study finds high-fat diet changes gut microflora, signals to brain

Athens, Ga. – According to a recent study, eating foods high in fat—good-tasting french fries, for example—changes the populations of bacteria innate to flora in the digestive tract, or gut, and alters signaling to the brain. The result: People no longer recognize that they are full, which can cause overeating, a leading cause of obesity.

“When we switch to a high-fat diet, we reorganize our brain circuits,” explained study co-author Krzysztof Czaja, an associate professor of neuroanatomy in the University of Georgia College of Veterinary Medicine. “We change our brain circuits by eating unbalanced foods, and we also induce the inflammation in brain regions responsible for feeding behavior. Those reorganized circuits and inflammation may alter satiety signaling.”

The findings from this study, which was conducted by researchers at UGA, Washington State University and Binghamton University, are being presented at the 23rd annual meeting of the Society for the Study of Ingestive Behavior July 7-11 in Denver.

So what happens to the microbiota in the intestines when someone switches to a high-fat diet? Czaja likens the microscopic phenomenon to how a sudden significant shift in temperature might impact the people who live in the affected area: Some people will be fine. Others will become ill.

“In the regular physiological state, many different strains of bacteria live in a balanced environment in our intestinal tract,” Czaja said. “They don’t overpopulate. There are little shifts, but in general this population is quite stable.

“When we start introducing a different diet, there is an immediate effect. Suddenly, different nutrients are changing the microenvironment in the gut, and some bacteria begin to overpopulate. Some sensitive bacteria begin to die, and some populations may even vanish. So, introducing a significant change in the gut microenvironment triggers a cascade of events that leads to this population switch.”

All of these changes result in a damage of gut-brain neural connections reflected by an inflammation and miscommunication between the gut and the brain, he said. It is not yet known whether this change is permanent, but Czaja and his colleagues plan to address this question in the future.

When it comes to diet and how it impacts health, Czaja says people should “think systemically. All of the components and receptors in the body are interconnected and should work in harmony. There is not a single receptor responsible for huge physiological outcomes.”

Throughout the history of mankind until just a few decades ago, the human body was used to foods derived from natural and whole sources, rather than artificial and highly processed, he said.

“We should be aware that on a high-fat (and high-carbohydrate) diet, balance in the intestinal microbiota and gut-brain communication—which was developing over thousands and thousands of years in humans and animals—has been interrupted by the introduction of modified foods. This leads to the confused brain and inappropriate satiety feedback and results in obesity.”

Co-authors on the study include E.M. Cooper, C. Vaughn and J.H. Peters of the department of integrative physiology and neuroscience at Washington State University; P.M. Di Lorenzo of the department of psychology, Binghamton University; and J.L. O’Loughlin and M.E. Konkel of the School of Molecular Biosciences, Washington State University.

The research was supported by the National Institute on Deafness and Other Communication Disorders under grant number 1R01DC013904. For an abstract of Czaja’s presentation, visit

For more information on the Society for the Study of Ingestive Behavior’s annual meeting, visit For more information on the UGA College of Veterinary Medicine, visit