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Depression scores ran about three points lower while 19 adults in a UCSF pilot cut ultra-processed food
UCSF researchers found depression scores about three PHQ-9 points lower when 19 adults cut ultra-processed food for four weeks. The result justifies the larger blinded trial the authors want; on its own it is too small to guide how depression is treated.
The Scientist · Science desk
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What happened
- Participants were randomly assigned to start with four weeks of usual eating or four weeks of cutting ultra-processed food, then switched to the other diet.
- Depression scores also fell during the usual-diet weeks, with average PHQ-9 dropping from 12.8 at the start to 8.68, so the diet effect is measured between the two periods.
- On a second depression scale, the MADRS, average scores were 18.9 during usual eating and 8.05 during the low-ultra-processed-food weeks.
- Every participant had high body weight and reported at least one metabolic abnormality.
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Why it matters
- constraint The 4.12-point fall on the usual diet alone is larger than the gap between the two diets, so any follow-up has to judge the diet against a control period and never against where patients started.
- constraint Participants knew which diet they were eating, so expectation and food are mixed together in these scores until a blinded design pulls them apart.
- decision Medication, therapy, exercise and sleep were held constant, so the evidence bears only on adding the diet to existing care and gives clinicians no basis for using it in place of treatment.
- cost Patients carry the effort: they rated the diet 5.74 for ease against 8.42 for usefulness, and a longer trial will have to show whether people keep it up past four weeks.
Twenty adults enrolled and 19 finished [1] [6]. Each person ate both ways, and the order was randomized [3]. That let the analysis adjust for baseline symptoms, diet order and study period, and the adjusted model produced the headline estimate [8]. On the nine-question PHQ-9, the raw gap was 3.15 points, between averages of 8.68 on the usual diet and 5.53 on the low-ultra-processed diet [1]. A third depression scale and an anxiety questionnaire also came in lower during the diet weeks [10].
On paper the diet change was large. Average scores on a questionnaire about highly processed food fell from 10.10 at baseline to 1.42 after the intervention [7], a drop of about 86% [3]. Participants shopped for themselves with guidance from the researchers [4]. Intake was self-reported, and the trial had no objective measure of how much ultra-processed food anyone ate [18].
The thing this doesn't tell you is which part of the change mattered. Eating less ultra-processed food also shifts sugar, fat and calorie intake, and additives or processing contaminants are other candidates; the study could not separate them [15]. Earlier observational studies linked higher ultra-processed food consumption with depression [11]. Here the diet was changed on purpose, in adults with an average age of about 44 who had lived with depression for nearly 13 years on average [2].
The diet takes effort to keep. Chagwedera said reducing ultra-processed food is hard "because it's highly palatable, cheap, and convenient" [12]. No adverse events were reported [23]. The team concluded the approach was feasible and acceptable, and a basis for larger trials [14].
I think that conclusion is the right size. Feasibility and acceptability were the primary outcomes, and the authors describe the depression and anxiety results as exploratory and hypothesis-generating [20]. They want the next study to be larger and blinded, to measure intake objectively and to investigate mechanisms [21]. The pilot was published in JAMA Psychiatry [22].
What to watch
- Whether the UCSF group runs the larger blinded trial it calls for, with an objective measure of ultra-processed food intake in place of a questionnaire.
- Whether the between-diet difference holds in people with depression who do not have high body weight or metabolic abnormalities.
- Whether follow-up work can separate sugar, fat, calories and additives as the part of the diet change linked to lower scores.