Twenty people with depression cut ultra-processed food by 85%. Their depression scores improved

A pilot crossover trial published in JAMA Psychiatry on 23 September 2026 asked 20 adults with major depressive disorder, who ate a large share of ultra-processed food, to cut it back. One group stayed on its usual diet for four weeks while the other switched to a diet low in ultra-processed foods; then the groups swapped. Participants chose and bought their own food, with guidance from the research team at the University of California, San Francisco.

According to the university's release, participants cut their ultra-processed food intake by more than 85% and showed moderate to large improvements on three different measures of depression while eating that way. Anxiety scores improved modestly. The group's average age was 44, 70% were women, 14 of the 20 also had anxiety, and all had a high BMI and at least one metabolic disorder.

The trial was built to test whether such a study can be done, not to prove that diet treats depression. Twenty people is a small group, everyone knew what they were eating, and a change of diet often comes with other changes in routine. The researchers plan a larger phase 2 trial, with enrolment expected to begin in 2028. Changing what you eat is not a replacement for depression treatment: keep to the care plan agreed with your doctor.