Reducing ultra-processed foods linked to lower depression scores

Researchers are investigating whether eating less ultra-processed food can help ease symptoms of depression. In a trial, participants diagnosed with depression reported fewer symptoms during a low ultra-processed food diet than during their usual diet.

Each dietary period lasted four weeks, allowing researchers to compare the two eating patterns in the same participants.

The study was led by Nyasha Chagwedera, a psychiatry researcher at the University of California, San Francisco (UCSF). It recruited 20 adults who regularly consumed substantial amounts of ultra-processed foods. Their average age was approximately 44, and they had lived with depression for an average of about 13 years.

Participants were randomly assigned to begin with one of two diets. One group ate as usual for four weeks, while the other reduced its intake of ultra-processed foods. They then switched diets.

With guidance from the researchers, participants purchased their own food. They agreed to keep their medication, therapy, exercise and sleep routines unchanged throughout the study.

Nineteen participants completed the trial. The average score on a questionnaire assessing ultra-processed food intake fell from 10.10 at baseline to 1.42 after the dietary intervention.

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

On the nine-item Patient Health Questionnaire (PHQ-9), the average score was 8.68 during the usual-diet period and 5.53 during the intervention. After accounting for baseline symptoms, diet order and study period, the analysis estimated a difference of about three points between the diets.

On another depression scale, the Montgomery–Åsberg Depression Rating Scale (MADRS), the average score was 18.9 during the usual diet and 8.05 during the low ultra-processed food diet.

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

Previous observational studies have linked higher ultra-processed food consumption with depression. In this trial, researchers examined what happened when people already living with depression changed their eating habits.

The intervention required participants to alter familiar routines. Packaged snacks and some ready-made products can be convenient when time and energy are limited, although not all processed foods are ultra-processed.

Chagwedera noted that reducing ultra-processed food intake can be challenging because these products are highly palatable, inexpensive and readily available.

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

Reducing ultra-processed foods may also change sugar, fat or calorie intake. Contaminants or additives associated with food processing are other possible factors. However, the study could not determine which aspects of the dietary change were responsible for the differences in symptoms.

Symptoms also declined during the usual-diet period compared with the start of the study. For example, the average PHQ-9 score was 12.8 at baseline and 8.68 during the usual-diet period.

Therefore, the reported dietary effect reflects the difference between the two diet periods; it does not mean that the entire improvement from baseline can be attributed to reducing ultra-processed foods.

The trial was small and not double-blinded. Participants knew which diet they were following, so their expectations may have influenced the results. Food intake was also self-reported, with no objective measure used to assess ultra-processed food consumption.

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

Feasibility and acceptability were the primary outcomes. Depression and anxiety measures were exploratory, and the authors described the findings as hypothesis-generating.

The researchers called for larger studies using objective measures of ultra-processed food intake and investigating the mechanisms that may explain the results.