A small preliminary study from the University of California, San Francisco adds to growing evidence that eating fewer ultra-processed foods may help reduce symptoms of depression.
Published on September 23 in JAMA PsychiatryThe study was funded by the National Institutes of Health. Researchers believe it is the first study to compare depression symptoms in the same participants before and after switching from their usual ultra-processed diet to healthier foods.
The pilot study included only 20 people, but senior author Andrew Krystal, MD, Ray and Dagmar Dolby Distinguished Professor in the departments of Psychiatry and Behavioral Sciences and Neurology at UCSF, said it “successfully established the feasibility of conducting this research in a larger-scale trial.”
Depression symptoms improved after major diet change
The participants reduced their consumption of ultra-processed foods by more than 85%. After doing so, they showed moderate to large improvements on three different measures of depression. Anxiety scores also improved modestly.
Ultra-processed foods include products such as packaged snacks, fast food, sugary drinks, and other industrially manufactured foods. These products may contain ingredients including preservatives, artificial colors, flavor enhancers and emulsifiers.
“Reducing the amount of ultra-processed foods in our diet can be challenging, because they are so tasty, cheap, and convenient,” said corresponding author Nyasha Chagwedera, MD, PhD, assistant professor in the UCSF Department of Psychiatry and Behavioral Sciences. “Ultra-processed foods activate dopamine, the pleasure hormone, which promotes desire. Food companies work with scientists to find just the right amount of sugar, salt and fat that makes you want to eat more and more.”
Testing the gut-brain connection
Participants had an average age of 44 years and 70% were women. In addition to depression, 14 participants also suffered from anxiety. All study participants had a high BMI and at least one metabolic disorder, such as hypertension, diabetes, or elevated LDL cholesterol.
The researchers divided the participants into two groups. One group maintained their usual diet for four weeks, while the other switched to a diet low in ultra-processed foods. Participants selected and purchased their own food with guidance from the research team. After four weeks, the groups switched diets.
Chagwedera, who founded the UCSF Metabolic and Mental Health Program, said one possible explanation for the connection between ultra-processed foods and depression involves what she described as a “leaky, unbalanced gut.” According to this idea, ultra-processed foods can damage the protective layer of the intestine.
“This intestinal damage can create chronic low-grade inflammation throughout the body that directly causes depression or makes people more vulnerable to it.”
“In other words, junk processing can damage the gut in ways that impact the brain.”
Larger depression trial planned
Because the study was small, the findings are still preliminary. The researchers now plan to investigate the effect in a larger group, with enrollment for phase 2 expected to begin in 2028.
Authors: Other UCSF authors include Eliana Kim, MD, Dorothy T. Chiu, PhD, Chengshi Jin, PhD, and Catherine Lee PhD. Other authors include Susannah Tye, PhD, of the University of Queensland, Australia, Mayo Clinic, and Emory University.
Funding: National Center for Advancing Translational Sciences, National Institutes of Health, through grant number UL1 TR001872 to UCSF-CTSI; NHLBI grant R38AG070171, NIMH grant R38AG070171, and the UCSF Weill Institute for Neurosciences.