Reducing Ultraprocessed Foods May Improve Depression and Anxiety Symptoms in Major Depressive Disorder: JAMA
USA: A small pilot crossover trial published in JAMA Psychiatry found that patients with major depressive disorder experienced reductions in depression and anxiety scores when they reduced their intake of ultra-processed foods, suggesting that dietary modification may have a role in supporting mental health.
The study, led by researchers from the University of California, San Francisco (UCSF), evaluated whether substantially reducing ultra-processed food (UPF) consumption was feasible and acceptable among people with major depressive disorder (MDD) who regularly consumed high amounts of these foods. The findings add to epidemiological evidence linking greater UPF consumption with a higher risk of depression, including a reported dose-response relationship.
The researchers noted that observational evidence alone cannot establish causation. However, biological pathways involving both peripheral and central mechanisms provide plausible explanations for a relationship between UPF consumption and depression, although a direct mechanistic connection has not been established.
The pilot crossover trial included 20 adults with MDD, with participants having a mean age of 44 years and 70% being women. Fourteen participants also had anxiety. All participants had a high body mass index and at least one metabolic condition, including hypertension, diabetes, or elevated low-density lipoprotein cholesterol.
Participants were assigned to either continue their usual diet for four weeks or follow a low-UPF diet. Those assigned to the dietary intervention received guidance from the research team while purchasing and preparing their own food. After four weeks, participants switched to the alternative diet, allowing each participant to experience both dietary conditions.
The findings were:
• Participants reduced their consumption of ultra-processed foods by more than 85% during the low-UPF dietary phase.
• Moderate-to-large improvements were observed across three measures of depressive symptoms.
• Anxiety scores also showed a modest improvement following the reduction in UPF intake.
• The pilot demonstrated that substantially reducing UPF consumption among patients with MDD was feasible and acceptable, supporting further investigation in larger clinical trials.
Ultraprocessed foods commonly include packaged snacks, fast foods, sugary drinks and other commercially manufactured products that may contain additives such as preservatives, artificial colors, flavor enhancers and emulsifiers. The researchers noted that reducing these foods can be difficult because they are generally convenient, inexpensive and highly palatable.
The authors proposed that changes in the gut may be one possible pathway connecting UPF consumption with mental health. Damage to the intestinal barrier and alterations in the gut environment could potentially contribute to chronic, low-grade inflammation, which may influence brain function and vulnerability to depressive symptoms. However, this remains a proposed mechanism rather than an established causal pathway.
The researchers emphasized that the study's small sample size and pilot design mean that the findings require confirmation in larger trials. The team expects to begin enrollment for a phase 2 study in 2028.
Overall, the trial provides preliminary clinical evidence that substantially reducing ultra-processed foods may be associated with improvements in depressive and anxiety symptoms, while highlighting the need for larger controlled studies to determine whether dietary UPF reduction can become a meaningful component of depression management.
Reference:
Chagwedera DN, Kim E, Chiu DT, et al. Reducing Ultraprocessed Foods From the Diets of Patients With Depression: A Pilot Crossover Trial. JAMA Psychiatry. Published online September 23, 2026. doi:10.1001/jamapsychiatry.2026.2320
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