How gut bacteria may trigger binge eating or weight gain

Certain gut bacteria may increase the risk that a person will binge eat and become obese, a new study suggests.

In a series of experiments, mice and humans with a propensity for binge eating had similar levels of two types of bacteria in their microbiomes — one detrimental and one beneficial — according to the report presented Thursday at a meeting of the Federation of European Neuroscience Societies and published in the journal Gut.

The researchers also found that if they increased the number of a type of beneficial bacteria called Blautia, they could prevent addictive eating behaviors from developing in mice.

The new findings are “very important because they show that this type of bacteria in effect protects against the development of compulsive food addiction,” said Elena Martin-Garcia, a senior study author and an associate professor at the Universitat Pompeu Fabra in Barcelona, Spain.

The team looked at both mice and humans initially to see if there were any consistent microbiome patterns.

While food addiction isn’t considered an official diagnosis, researchers generally recognize that some people have a hard time controlling their consumption of highly processed foods such as sweets and snacks.

Future experiments by the team will explore whether increasing Blautia bacteria in humans might help curb binge eating.

Does the gut talk to the brain?

The researchers aren’t sure how the bacteria protect against the development of compulsive eating, but they have theories.

“We speculate that the gut talks with the brain,” said Martin-Garcia, a researcher at the university’s Laboratory of Neuropharmacology-NeuroPhar. “And that may change the function of some brain areas, such as the prefrontal cortex, which is involved in self-control.”

The researchers recruited 88 people, some of whom were food addicted, along with a collection of 103 mice, including some with compulsive eating habits.

The participants were white women and men from Spain with an average age of 48. Thirty six of the participants were obese; 52 were normal weight.

As it turns out, a certain proportion of mice in nature develop food bingeing, said Dr. Rafael Maldonado, the study’s other senior author and head of the Laboratory Neuropharmacology-NeuroPhar.

“It results from a combination of genetics and environmental factors,” said Maldonado, a professor at the Universitat Pompeu Fabra. “The ones that have a genetic predisposition can lose control of eating if they are exposed to unhealthy food that is obesogenic.”

Obesogenic foods in the human diet typically have high levels of fat and carbohydrates, such as sugary drinks and desserts and foods containing high amounts of saturated fats and refined carbohydrates, including pizza, fries, burgers and hot dogs.

The humans and mice with symptoms of food addiction had similar patterns of microbiome bacteria that were different from the humans and rodents with a healthy relationship with food.

In the next experiment, the researchers exposed a group of mice to “obesogenic” food, which, along with a high fat and carb composition, also contained chocolate. About 22% of the mice became compulsive eaters.

“They became crazy for the food,” Martin-Garcia said. “They kept banging on the lever asking for more.”

Then the researchers exposed a group of mice that had been tweaked to have higher levels of the beneficial bacteria in their guts to the same food. None of them became compulsive eaters.

The next step, Martin-Garcia said, is to increase the levels of the beneficial bacteria in mice that already have an eating disorder to see if the bacteria can help them eat more normally.

If that pans out, the group would set up a trial to test whether tweaking the bacteria in the human microbiome could help reverse the inability to control eating, she said.

Scientists have come to appreciate more how microbes in the gut can affect health and behavior, said Dr. Mariana Byndloss, co-director of the Vanderbilt Microbiome Innovation Center. “The relationship between the gut and the brain is a very hot topic right now,” Byndloss said.

While the authors have shown that there is an association between certain bacteria and binge eating, the bacteria may not be directly causing the problem, said Byndloss, an assistant professor at the Vanderbilt University Medical Center.

Low levels of the bacteria could be causing issues further down the road that then lead to addiction problems or the low levels may simply be a marker for compulsive eating.

“There’s definitely been strong evidence that microbiota contribute to outcomes in different diseases,” Byndloss said. “But we also know that healthy dietary habits — consuming a diet that is rich in vegetables and complex types of fiber and low in processed foods and saturated fat — promotes a healthier microbiome that can protect against chronic diseases.”

Previous research has linked bacteria in the microbiome to a number of diseases, said Dr. Daniel Wang, a microbiome expert and an assistant professor at Brigham and Women’s Hospital, Harvard Medical School and the T.H. Chan School of Public Health. On June 25, Wang’s group published research in Nature Medicine linking certain patterns of bacteria in the gut to a higher risk of diabetes.

“This is a very novel and interesting study,” Wang said. “Their major finding, linking the microbiome to food addiction, is an area that is underexplored.”

Linda Carroll

Linda Carroll is a regular health contributor to NBC News. She is coauthor of "The Concussion Crisis: Anatomy of a Silent Epidemic" and "Out of the Clouds: The Unlikely Horseman and the Unwanted Colt Who Conquered the Sport of Kings."