One Diet Change May Ease Depression Symptoms in Just 4 Weeks, Small Trial Finds

A packet of snacks. A sugary drink. A meal ready in minutes. Ultra-processed foods make life easier in the kitchen. Researchers are investigating whether eating fewer of them could also make a difference to depression symptoms.

In a pilot trial, people diagnosed with depression had lower symptom scores during a diet low in ultra-processed foods than during their usual diet.

Each dietary period lasted four weeks, giving researchers a chance to compare two eating patterns in the same people.

The study, led by psychiatry researcher Nyasha Chagwedera at the University of California, San Francisco (UCSF), recruited 20 adults who consumed substantial amounts of ultra-processed foods.

Their average age was approximately 44, and they had lived with depression for an average of nearly 13 years.

Participants were randomly assigned to start with one of two diets. One group ate as usual for four weeks, while the other reduced ultra-processed foods. Then they switched.

Participants bought their own food with guidance from researchers. They agreed to keep medications, therapy, exercise, and sleep unchanged throughout the study.

Nineteen people completed the trial. Average scores on a questionnaire assessing highly processed food consumption dropped from 10.10 at baseline to 1.42 after the intervention.

Three separate depression assessments recorded lower scores during the low-ultra-processed-food period than during the usual-diet period.

On the nine-question PHQ-9 assessment, average scores were 8.68 during the usual diet and 5.53 during the dietary intervention. An analysis accounting for baseline symptoms, diet order, and study period estimated a difference of about three points between the diets.

On another depression assessment, the MADRS, average scores were 18.9 during the usual diet and 8.05 during the low-ultra-processed-food diet.

The third depression assessment and an anxiety questionnaire also recorded lower scores during the dietary intervention.

Earlier observational studies have linked higher ultra-processed food consumption with depression. Here, researchers explored what happens when people already living with depression change their eating habits.

That meant asking participants to alter familiar routines. Packaged snacks and some ready-made products offer convenient options when time and energy are limited, though not all processed foods are ultra-processed.

Reducing ultra-processed food can be challenging "because it's highly palatable, cheap, and convenient", Chagwedera explains.

Participants' average rating for the ease of the intervention was 5.74. Their average rating for its usefulness was 8.42, and no adverse events were reported.

The researchers concluded that the approach was feasible and acceptable, providing a basis for larger trials.

Reducing ultra-processed foods can also change sugar, fat, or calorie intake. Processing-related contaminants or additives are other possible factors. This study could not determine which aspects of the dietary change mattered.

Symptoms were also lower during the usual-diet period than at baseline. For example, average PHQ-9 scores were 12.8 at the start of the study, compared with 8.68 during the usual diet.

The reported dietary effect therefore concerns the difference between the two diet periods, rather than attributing the entire improvement from baseline to reducing ultra-processed foods.

The trial was small and unblinded: participants knew which diet they were following, so expectations could have influenced the results. Food consumption was self-reported, with no objective measure of ultra-processed food intake.

All participants had high body weight and reported at least one metabolic abnormality. The findings may therefore not apply equally to other people with depression.

The primary outcomes were feasibility and acceptability. Depression and anxiety outcomes were exploratory, and the authors describe these findings as hypothesis-generating.

The researchers call for larger, blinded studies that use objective measures of ultra-processed food intake and investigate the mechanisms behind the results.

The research has been published in JAMA Psychiatry.