Recent studies from North American research teams have linked ultra-processed food intake to depression, anxiety and subtle brain changes. The findings, published in journals including JAMA Psychiatry and JAMA Network Open, suggest that what people eat may shape mood and cognitive health, not just weight.

What did the California trial find?

A small University of California, San Francisco, study followed 20 overweight adults with depressive symptoms and at least one metabolic condition, such as high blood pressure or elevated cholesterol. Participants averaged about 44 years old, and 14 were women.

Read also Reducing Ultra-Processed Foods May Improve Depression Symptoms

In a crossover design, one group kept its usual diet for four weeks while the other cut back on packaged snacks, fast food and sugary drinks under researcher guidance. The groups then swapped. Nineteen participants finished the study.

Those who reduced ultra-processed food intake by more than 85% reported moderate to significant improvement in depression symptoms, with some also seeing slightly less anxiety, according to the report in JAMA Psychiatry. The work was funded by the National Institutes of Health.

Why might food affect mood?

One hypothesis centers on the gut. Lead author Dr. Nyasha Chagwedera said these foods may damage the intestinal lining, creating what she called a "leaky, unbalanced gut." That damage could trigger low-grade inflammation affecting the brain, she said, though the idea remains unproven.

Neuropsychologist Sanam Hafeez, who was not involved, told the Epoch Times that the speed of change was striking. She said the results challenge the view that food only affects physical markers like weight and blood sugar.

Critics note the trial could not separate the diet's effect from weight change or the extra attention participants received, and the sample was small.

What about the brain scans?

A Canadian study of 8,783 adults aged 35 to 69, published in JAMA Network Open, found that the heaviest consumers of ultra-processed foods had a 40% higher risk of silent brain lesions, such as small vessel disease. Lesions appeared in about 11% of heavy consumers versus 8% of low consumers, and can precede memory problems.

Processed meats, sugary drinks, sweet dairy desserts and industrial breakfast products were flagged as the highest-risk categories.

Separately, a JAMA Network Open study of 46 normal-weight children found that those getting more calories from ultra-processed foods showed stronger reward-system responses to food images, linked to later gains in body fat.

FAQ

Are all processed foods unhealthy?

No. Dietitian Michelle Routhenstein noted that processing is not inherently negative, since many nutritious foods undergo some processing.

How quickly could diet changes help?

In the California trial, participants reported mood improvements after four weeks, though the study was small.