A small pilot study from UC San Francisco suggests that cutting ultra-processed foods from your diet might ease depression. The study, published Sept. 23 in JAMA Psychiatry, followed 20 people with depression who dramatically reduced their intake of packaged snacks, fast food and industrially manufactured foods. They showed moderate to large improvements across three measures of depression, and anxiety scores also moved up modestly.
The research was funded by the National Institutes of Health. Senior author Andrew Krystal, MD, Ray and Dagmar Dolby Distinguished Professor in UCSF’s departments of Psychiatry and Behavioral Sciences and Neurology, said the pilot “successfully established the viability of carrying out this research in a larger-scale trial.”
The Diet Change
Participants cut their intake of ultra-processed foods by more than 85%. Ultra-processed foods include products containing preservatives, artificial coloring, flavor enhancers and emulsifiers. They are the packaged snacks, fast food meals and sugary drinks that fill supermarket aisles.
Corresponding author Nyasha Chagwedera, MD, PhD, assistant professor in the UCSF Department of Psychiatry and Behavioral Sciences, noted that reducing these foods is difficult. “Reducing the amount of ultra-processed food in our diet can be challenging, because it’s highly palatable, cheap, and convenient,” she said. “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.”
The participants chose and bought their own food with guidance from the research team. They switched diets in sequence, with one group staying on its usual diet for four weeks while the other went low in ultra-processed foods. Then they swapped back. This design let researchers compare the same people before and after the diet change, which the team says has not been done before in this field.
What the Numbers Show
The study included only 20 people, so the findings are preliminary. But the direction of the results is consistent across multiple measures. Depression symptoms improved moderately to largely, and anxiety scores moved up modestly.
The participants had an average age of 44, and 70% were female. Fourteen of the 20 also had anxiety. Everyone in the study had a high BMI and at least one metabolic disorder — hypertension, diabetes or elevated LDL cholesterol.
The improvement in depression was moderate to large across three different measures. Anxiety showed a smaller but still notable upward trend. Both changes occurred after the diet shift, and the design of the study — comparing each person to themselves before and after — strengthens the case that the food change drove the result.
The Gut-Brain Explanation
Chagwedera, who founded the UCSF Metabolic and Mental Health Program, offered one possible explanation for the link between ultra-processed food and depression. She described it 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 hypothesis is straightforward. Processed foods may disrupt the gut lining, leading to low-grade inflammation that travels to the brain. That inflammation could then worsen mood or make people more sensitive to stress. The study does not prove this pathway — it documents the correlation between diet and symptoms — but the researchers describe it as their working theory.
Who Funded the Work
The study received funding from the National Center for Advancing Translational Sciences, National Institutes of Health, through UCSF-CTSI Grant Number UL1 TR001872; NHLBI grant R38AG070171; and NIMH grant R38AG070171. The study was also supported by the UCSF Weill Institute of Neurosciences.
What Comes Next
Because the study was small, the findings remain preliminary. The researchers now plan to test the effect in a larger group, with enrollment for phase 2 expected to begin in 2028.
Additional UCSF authors include Eliana Kim, MD, Dorothy T. Chiu, PhD, Chengshi Jin, PhD, and Catherine Lee PhD. Other authors are Susannah Tye, PhD, of the University of Queensland, Australia, Mayo Clinic and Emory University.
The Bottom Line
This is a small study, and small studies are noisy. But the direction of the results — depression and anxiety improving after people cut ultra-processed foods — is consistent across multiple measures.
The findings are promising, but they are not a prescription. The study looked at a specific population of people with depression and metabolic disorders, and the results need to be confirmed in a bigger, more diverse group before anyone should treat diet as a stand-in for medication or therapy.
Still, the basic idea — that what you eat affects how you feel — is one worth paying attention to. The brain responds to what goes into it, and the study documents a clear pattern in this small group.
The study is available online at JAMA Psychiatry, with DOI: 10.1001/jamapsychiatry.2026.2320. For now, the takeaway is simple: the early data suggests that eating fewer ultra-processed foods may help ease depression.
Key Facts Box
– Study size: 20 participants
– Diet reduction: More than 85%
– Symptom improvement: Moderate to large across three depression measures
– Anxiety improvement: Modest
– Funding: National Institutes of Health
– Phase 2 enrollment: Expected to begin in 2028
– DOI: 10.1001/jamapsychiatry.2026.2320
What the Study Found
– Participants cut ultra-processed foods by more than 85%
– Depression symptoms improved moderately to largely
– Anxiety scores improved modestly
– Average age: 44
– 70% female
– 14 of 20 had anxiety
– All had a high BMI and at least one metabolic disorder
Who Led the Research
– Senior author: Andrew Krystal, MD, Ray and Dagmar Dolby Distinguished Professor
– Corresponding author: Nyasha Chagwedera, MD, PhD, assistant professor
– UCSF co-authors: Eliana Kim, MD; Dorothy T. Chiu, PhD; Chengshi Jin, PhD; Catherine Lee PhD
– Other authors: Susannah Tye, PhD, University of Queensland, Australia, Mayo Clinic, Emory University
The paper’s honest reaction to this story is RELIEF: A small pilot study found that people with depression who cut ultra-processed foods by 85% showed notable symptom improvement, offering a promising dietary path toward mental health.
Source material: “Could quitting ultra-processed food boost your mental health?,” ScienceDaily.
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