A small preliminary study from UC San Francisco adds to mounting evidence that eating fewer ultra-processed foods may help reduce symptoms of depression.
Published Sept. 23 in JAMA Psychiatry, the 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 they moved 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 UCSF’s departments of Psychiatry and Behavioral Sciences and Neurology, said it “successfully established the viability of carrying out this research in a larger-scale trial.”
Depression Symptoms Improved After a Major Diet Shift
Participants cut their intake of ultra-processed foods by more than 85%. After doing so, they showed moderate to large improvements across 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 coloring, flavor enhancers, and emulsifiers.
“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, PhD, assistant professor in the UCSF Department of Psychiatry and Behavioral Sciences. “Ultra-processed food triggers dopamine, the pleasure hormone, which promotes craving. 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.”
Testing the Gut-Brain Connection
The participants had an average age of 44, and 70% were female. Along with depression, 14 participants also had anxiety. Everyone in the study had a high BMI and at least one metabolic disorder — such as hypertension, diabetes, or elevated LDL cholesterol.
Researchers divided the participants into two groups. One group stayed on its usual diet for four weeks, while the other switched to a diet low in ultra-processed foods. Participants selected and bought 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 food and depression involves what she described as a “leaky, out-of-balance gut.” According to this idea, ultra-processed foods may damage the protective lining of the gut.
“This gut damage can create low-grade, chronic inflammation throughout the body that either directly causes depression or makes people more vulnerable to it.”
“In other words, junky processing may harm your gut in ways that ripple up to your 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: Additional UCSF authors include Eliana Kim, MD, Dorothy T. Chiu, PhD, Chengshi Jin, PhD, Catherine Lee PhD. Other authors are 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 UCSF-CTSI Grant Number UL1 TR001872; NHLBI grant R38AG070171, NIMH grant R38AG070171, and the UCSF Weill Institute of Neurosciences.
