Low-UPF diet links to lower depression scores in 20-person study

A JAMA Psychiatry study published Sept. 23 found that 20 adults with depression had lower symptom scores while eating a low-ultra-processed-food diet than during their usual diet.

Evidence grade: Moderate (consistent observational data or small trials). The Patient Health Questionnaire-9, a nine-item depression symptom scale, averaged 5.53 during the low-UPF phase, compared with 8.68 during the usual-diet phase.

The study enrolled adults ages 18 to 80 with a primary diagnosis of depression, a PHQ-9 score of at least 5, high ultra-processed-food intake and at least one self-reported metabolic abnormality. Nineteen participants completed the study, and the average age was 44.

Participants ate both their usual diet and a low-UPF diet in separate phases, with the order randomly assigned. They had to agree not to change medications, therapy, exercise or sleep during the study.

Ultra-processed foods, or UPFs, do not have one universally accepted definition. The NOVA classification system describes them as industrial formulations made mainly from substances extracted or derived from foods, often with additives not typically used in home cooking; examples include soft drinks, packaged snacks, candy, sausages, hot dogs and pastries.

The finding adds to earlier research associating high UPF intake with depression, anxiety, eating disorders and other mental-health conditions. In this study, participants reduced UPF intake by more than 85% and had lower depression scores across three standard measures during the low-UPF phase.

Michelle Routhenstein, Preventive Cardiology Dietitian at Entirely Nourished, who was not involved in the study, told Healthline that the distinction between processing levels matters. “Processing is not inherently negative. Many nutritious foods are processed in some way.”

“I would not encourage people to simply label a food as ‘processed’ or ‘unprocessed’ and make decisions based on that label alone,” Routhenstein said. “I prefer to look at the overall dietary pattern, the nutritional value of the food, and what role that food plays in the diet. A packaged food can still provide meaningful nutrients and be part of an overall nutritious eating pattern.”

Researchers and outside experts cited in the Healthline report described several possible pathways under investigation, including nutrient quality, inflammation, metabolic health and the gut-brain axis. The report said UPFs are often low in fiber, vitamins and minerals, which can be relevant to brain health.

The result most directly applies to adults like those studied: people with depression, high UPF intake and at least one self-reported metabolic abnormality. It does not show the same effect in people without depression, children, pregnant people or adults with different dietary patterns.

The study cannot show which part of the low-UPF diet contributed to symptom changes. Its limits include the small sample, self-reported dietary data and uncertainty over whether reducing UPFs directly affected symptoms or whether other changes in the overall diet mattered.

The researchers said larger studies are needed to determine whether lowering UPF intake can improve depression symptoms. The supplied Healthline report did not provide funding or declared conflict-of-interest details for the JAMA Psychiatry study.

Source: Consumer-health news article, Healthline News, Oct. 3, 2026; study, JAMA Psychiatry, Sept. 23, 2026.

Atlas360 reports health research and does not provide medical advice.