A pack of snacks. A sweet drink. A meal ready in minutes. Ultra-processed foods make life in the kitchen easier. Researchers are studying whether eating less could also make a difference in depression symptoms.
In a pilot trial, people diagnosed with depression had lower symptom scores on a diet low in ultra-processed foods than on their usual diet.
Each dietary period lasted four weeks, which allowed researchers to compare two eating habits in the same people.
The study, led by psychiatry researcher Nyasha Chagwedera of the University of California, San Francisco (UCSF), recruited 20 adults consuming significant amounts of ultra-processed foods.
Their average age was around 44 and they had been living with depression for almost 13 years on average.
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 changed.
Participants purchased their own food with advice from researchers. They agreed to keep medications, therapy, exercise, and sleep unchanged throughout the study.
Nineteen people completed the trial. Mean scores on a questionnaire assessing consumption of highly processed foods increased from 10.10 at baseline to 1.42 after the intervention.
Three separate depression assessments recorded lower scores during the low ultra-processed food intake period than during the usual diet period.
On the nine-question PHQ-9 assessment, mean 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 diets.
In another depression assessment, the MADRS, mean scores were 18.9 with the usual diet and 8.05 with the diet low in ultra-processed foods.
The third depression assessment and an anxiety questionnaire also had lower scores during the dietary intervention.
Previous observational studies have linked higher consumption of ultra-processed foods to depression. Here, researchers explored what happens when people already suffering from depression change their eating habits.
This meant asking participants to modify their familiar routines. Packaged snacks and some ready-made products offer convenient options when time and energy are limited, although not all processed foods are ultra-processed.
Cutting back on ultra-processed foods can be a challenge “because they’re so tasty, cheap and convenient,” says Chagwedera.
Participants’ average rating for ease of 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-scale 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 dietary change were important.
Symptoms were also weaker during the usual diet period than at baseline. For example, mean PHQ-9 scores were 12.8 at the start of the study, compared to 8.68 during the usual diet.
The reported dietary effect therefore relates to the difference between the two diet periods, rather than attributing the entire improvement from baseline to the reduction in ultra-processed foods.
The trial was small and unblinded: participants knew what diet they were following, so expectations could have influenced the results. Food consumption was self-reported, with no objective measurement of ultra-processed food consumption.
All participants had high body weight and reported at least one metabolic abnormality. The results may therefore not apply in the same way to other people suffering from depression.
The primary outcome measures were feasibility and acceptability. The depression and anxiety findings were exploratory and the authors describe these findings as hypothesis generating.
Researchers are calling for larger, blinded studies that use objective measures of ultra-processed food consumption and investigate the mechanisms behind the findings.
The research was published in JAMA Psychiatry.
This article was fact-checked by Rebecca Dyer and edited by Rebecca Dyer. Although we are proud of our process, we are only human. If you spot an error, please let us know.
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