Cutting ultra-processed foods may improve symptoms of depression

A preliminary study led by UC San Francisco adds to growing evidence that reducing ultra-processed food may improve symptoms of depression.

Published Sept. 23 in JAMA Psychiatry, the study, which is funded by the National Institutes of Health, is believed to be the first to compare symptoms in people with depression before and after they switched from their regular ultra-processed diet to healthier food.

Although the pilot study comprised just 20 people, it "successfully established the viability of carrying out this research in a larger-scale trial," said senior author Andrew Krystal, MD, Ray and Dagmar Dolby Distinguished Professor in UCSF's departments of Psychiatry and Behavioral Sciences and Neurology.

Participants reduced ultra-processed food intake by more than 85% and experienced moderate to large improvements across three measures of depression. Anxiety scores also improved modestly. 

Ultra-processed food includes packaged snacks, fast food, sugary beverages, and other industrially manufactured items that may contain preservatives, artificial coloring, flavor enhancers, and emulsifiers.

Reducing the amount of ultra-processed food in our diet can be challenging, because it's highly palatable, cheap, and convenient. Ultra-processed food triggers dopamine, the pleasure hormone, which promotes craving. Food companies work with scientists to find just the right amount of sugar, salt, and fat that make you want to eat more and more."

Nyasha Chagwedera, MD, PhD, corresponding author, assistant professor, UCSF Department of Psychiatry and Behavioral Sciences

The gut-brain connection

The average age of the study participants was 44 and 70% were female. In addition to depression, 14 participants had anxiety, and all had a high BMI and at least one metabolic disorder - such as hypertension, diabetes, or elevated LDL cholesterol.

Participants were divided into two groups: one continued with their regular diet for four weeks, while the other shifted to a low ultra-processed diet, which they shopped for and purchased themselves with guidance from researchers. After four weeks, the two groups swapped diets.

The link between ultra-processed food and depression may be explained by a "leaky, out-of-balance gut," caused by damage from the food to the gut's protective lining, according to Chagwedera, who is the founder of the UCSF Metabolic and Mental Health Program. "This gut damage can create low-grade, chronic inflammation throughout the body that either directly causes depression or makes people more vulnerable to it."

"In other words, junky processing may harm your gut in ways that ripple up to your brain."

The researchers expect to start enrollment in phase 2 of the study in 2028.