Cutting Out Ultra-Processed Foods For One Month Reduced Depression Scores By More Than Half.
A small clinical trial from the University of California, San Francisco, published in JAMA Psychiatry, found that adults with depression who spent a month eating very little ultra-processed food had significantly lower depression scores than after a month eating their usual diet, a result that appeared consistently across three separate depression measurement scales including one scored by a clinician. The trial enrolled 20 adults who all had depression, all scored high on a diet questionnaire for ultra-processed food consumption, and all carried extra body weight. Their average age was around 44, and on average they had lived with depression for approximately 13 years. Half spent four weeks eating a low ultra-processed food diet while the other half ate as usual, then they swapped, with the order set randomly. Participants shopped for their own food with guidance from researchers. Everyone kept their medication, therapy, exercise, and sleep the same throughout, meaning the only variable changing between the two conditions was the diet. On a standard 27-point depression questionnaire, the group averaged 12.8 at the start, 8.7 after the usual diet month, and 5.5 after the low ultra-processed month. On the clinician-scored scale, which runs to 60, the group averaged 22 at the start, 19 after the usual diet month, and 8 after the low ultra-processed month. Anxiety scores also dropped further during the low ultra-processed period. No harmful side effects were reported, and 19 of the 20 participants finished the trial.
Lead author Nyasha Chagwedera, an assistant professor in UCSF's Department of Psychiatry and Behavioral Sciences and founder of the UCSF Metabolic and Mental Health Program, was clear about what the results do and do not show. The trial was designed primarily as a feasibility study, meaning its main goal was to find out whether a larger trial could work: whether people would enroll, stay in, actually cut back on ultra-processed food, and find the approach acceptable. The mood results were described by the authors as exploratory and hypothesis-generating rather than definitive. The sample of 20 people is too small to draw firm conclusions, everyone in the trial knew which diet they were on, and what participants ate was self-reported rather than objectively measured. The group was also specific, combining depression with excess body weight, so the results do not yet speak to people with depression who do not carry extra weight. Chagwedera proposed one possible biological mechanism involving what she described as a leaky gut, in which ultra-processed foods may damage the gut's protective lining and trigger low-grade chronic inflammation that either causes or worsens depression, a pathway that has supporting evidence in other research but was not directly measured in this trial. She also noted that cutting back on ultra-processed food is genuinely hard, because food companies design their products to trigger dopamine responses that drive repeated consumption, and the volunteers in her trial rated the dietary change as useful but not easy. The next phase of the research is expected to begin enrolling in 2028 in a larger, more rigorously designed study. The early signal from this trial is promising enough that it is worth pursuing.
