Cutting back hard on ultra-processed foods was linked to noticeable improvements in depression symptoms in a small preliminary study from UC San Francisco.
The study, published Sept. 23 in JAMA Psychiatry and funded by the National Institutes of Health, compared depression symptoms in the same participants before and after they moved from their usual ultra-processed diet to healthier foods. Researchers said they believe it is the first study to do that.
The pilot study included 20 people. 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.”
Participants cut their intake of ultra-processed foods by more than 85 percent. After that, 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.”
Participants had an average age of 44, and 70 percent 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 split 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 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,” she said.
“In other words, junky processing may harm your gut in ways that ripple up to your brain.”
The findings are preliminary because the study was small. Researchers plan to investigate the effect in a larger group, with enrollment for phase 2 expected to begin in 2028.
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