Cutting back on ultra-processed foods may do more than improve physical health, it could also help improve symptoms of depression.
Cutting back on ultra-processed foods may do more than improve physical health, it could also help improve symptoms of depression, according to a preliminary study led by researchers at the University of California, San Francisco.
Published in JAMA Psychiatry, the study is believed to be the first to compare depression symptoms in people before and after they substantially reduced their intake of ultra-processed foods. Although the pilot study included only 20 participants, researchers found that those who dramatically reduced their consumption experienced moderate to large improvements in several measures of depression. Anxiety symptoms also improved modestly.
The findings add to growing research examining the connection between diet and mental health and suggest that what we eat may influence how we feel.
“Reducing the amount of ultra-processed food in our diet can be challenging, because it's highly palatable, cheap and convenient,” said corresponding author Nyasha Chagwedera, MD, Ph.D., assistant professor in the UCSF Department of Psychiatry and Behavioral Sciences.
Ultra-processed foods include many packaged snacks, fast foods, sugary beverages and other highly manufactured products. They often contain ingredients such as preservatives, artificial colors, flavor enhancers and emulsifiers.
Chagwedera noted that these foods are designed to be highly appealing and can encourage cravings.
“Ultra-processed food triggers dopamine, the pleasure hormone, which promotes craving,” she said. “Food companies work with scientists to find just the right amount of sugar, salt and fat that make you want to eat more and more.”
The study participants had an average age of 44, and 70% were women. All participants had a high body mass index and at least one metabolic disorder, such as high blood pressure, diabetes or elevated LDL cholesterol. Fourteen participants also had anxiety in addition to depression.
Researchers divided the participants into two groups. One group continued eating its usual diet for four weeks, while the other switched to a diet containing very little ultra-processed food. Participants purchased and prepared their own food with guidance from the research team.
After four weeks, the groups switched diets.
Overall, participants reduced their ultra-processed food intake by more than 85%. During the periods when they followed the lower ultra-processed food diet, researchers observed moderate to large improvements across three different measures of depression. Anxiety scores also showed a modest improvement.
Because only 20 people participated, the findings should be considered preliminary. However, senior author Andrew Krystal, MD, Ray and Dagmar Dolby Distinguished Professor in UCSF's departments of Psychiatry and Behavioral Sciences and Neurology, said the study successfully demonstrated that a larger clinical trial is feasible.
One possible explanation for the relationship between ultra-processed foods and depression involves the gut-brain connection.
Researchers propose that diets high in ultra-processed foods may negatively affect the gut's protective lining and contribute to an imbalance in the gut. This could potentially promote low-grade, chronic inflammation throughout the body.
According to Chagwedera, this inflammation could directly contribute to depression or make someone more vulnerable to developing depressive symptoms.
The idea reflects growing scientific interest in the gut-brain connection—the complex communication system linking the digestive system and brain.
In other words, the effects of a highly processed diet may extend beyond weight and metabolic health. Changes taking place in the gut could potentially influence inflammation, brain function and mental well-being.
More research is needed to determine exactly how these factors are connected and whether reducing ultra-processed foods can consistently improve depression in larger groups of people.
Researchers expect to begin enrollment for Phase II of the study in 2028. If larger trials confirm the initial findings, dietary changes could become an important part of how researchers approach the relationship between nutrition and mental health.
