Obese mice exhibited more anxiety-like behaviors, such as increased freezing—a defensive posture rodents adopt when sensing a threat—compared to their lean counterparts
As global obesity rates surge, new research suggests that being overweight may not only impact physical health but could also significantly impair brain function and increase the risk of anxiety. The study, conducted in mice, indicates that obesity-related changes in brain signaling and gut microbiota may play a key role in affecting mental health.
The findings, presented at NUTRITION 2025, the flagship annual meeting of the American Society for Nutrition in Orlando, Florida, provide fresh insights into the complex relationship between diet, brain health, and emotional well-being.
“Our results show that obesity can lead to anxiety-like behavior, potentially due to altered brain function and changes in gut health,” said Desiree Wanders, Associate Professor and Chair of Nutrition at Georgia State University in the US. While obesity is already known to raise the risk of type 2 diabetes, cardiovascular disease, and certain cancers, this new study zeroes in on its potential neurological consequences. Using a mouse model that replicates many of the obesity-related conditions seen in humans, researchers tracked changes in behavior, brain chemistry, and gut microbiota over a 21-week period.
The study involved two groups of six-week-old mice. One group (16 mice) was fed a low-fat diet, while the other group (16 mice) was placed on a high-fat diet designed to induce obesity. As expected, the high-fat diet group gained significantly more weight and accumulated more body fat than the low-fat diet group. However, the most telling findings emerged during behavioral testing.
Obese mice exhibited more anxiety-like behaviors, such as increased freezing—a defensive posture rodents adopt when sensing a threat—compared to their lean counterparts. These mice also displayed altered signaling in the hypothalamus, the brain region responsible for regulating metabolism, which the researchers believe may contribute to cognitive impairments.
Beyond the brain, researchers also noted striking differences in the gut microbiota of the obese mice. “Gut bacteria play a critical role in regulating everything from digestion to immune response to brain chemistry,” said Wanders. “Disruptions to this delicate ecosystem can have far-reaching consequences.”
The gut-brain axis—the bidirectional communication pathway between the gastrointestinal tract and the brain—is increasingly recognized as a crucial factor in mental and neurological health. This study adds to a growing body of evidence suggesting that poor dietary choices and obesity can disrupt this axis, potentially leading to mood disorders and reduced cognitive performance.
“These findings carry significant public health implications,” Wanders emphasized. “Understanding how obesity affects mental health through changes in gut bacteria and brain function can help shape more effective prevention and intervention strategies, especially among children and adolescents, who are increasingly vulnerable to both obesity and anxiety.”
The research team hopes their findings will lead to further studies exploring the gut-brain connection in humans and promote policy initiatives that prioritize nutritional education and early intervention to combat the dual burden of obesity and mental health disorders.
