Does Cutting Ultra-Processed Food Help Depression?

Twenty people with depression dramatically reduced the ultra-processed food in their diets, and their symptoms improved. It is the first experimental signal that cutting UPF may help, but the trial was designed to show that the experiment could be done, not that changing your diet treats depression.

TL;DR

• The new trial is small but notable. Twenty adults with depression took part in a crossover study comparing four weeks of their usual diet with four weeks eating substantially less ultra-processed food.
• Depression and anxiety scores were lower during the low-UPF period. Improvements appeared across three separate depression measures, with smaller improvements in anxiety.
• But it wasn't blinded. Participants knew which phase they were in, received guidance and attention, bought their own food and reported what they ate.
• The researchers are cautious. Mood was an exploratory outcome in a trial whose stated purpose was to test feasibility and acceptability.
• A UK trial has tested processing more tightly. In UPDATE, 55 adults in England were given two eight-week diets built to the same national guidance, one minimally processed and one ultra-processed, and lost about twice as much weight on the minimally processed one.
• The observational literature is enormous. A recent analysis pooled 51 prospective cohorts containing almost 8.82 million adults and linked higher UPF consumption with a range of adverse outcomes.
• None of it settles causation. What exists is a feasibility signal, a feeding trial about weight, and millions of people whose diets differ in many ways at once.

Twenty People Changed Their Diets

The association between ultra-processed food and poor health has become hard to ignore, with study after study linking higher consumption to obesity, cardiovascular disease, diabetes and, increasingly, depression. Most of those studies share the same limitation: they observe what people eat and what happens afterwards. A trial published in JAMA Psychiatry on 23 September took a different approach. Researchers at the University of California, San Francisco, led by Nyasha Chagwedera, enrolled 20 adults with a primary diagnosis of depression who were also eating large amounts of ultra-processed food. To qualify, participants had to be aged 18 to 80, score at least 5 on the PHQ-9 depression questionnaire, fall in the top tertile of UPF consumption on a screening questionnaire for highly processed food, and report at least one metabolic abnormality. Nineteen completed the study.

The design was an open-label, order-randomised crossover: each participant spent four weeks on their usual diet and four weeks on a low-UPF intervention, in a random order. Rather than being handed two sets of meals, they shopped for and prepared their own food after a 45-minute session with a physician on cutting foods in the NOVA system's ultra-processed category, with phone check-ins during the intervention.

The dietary change was substantial. Mean scores on the screening questionnaire fell from 10.10 at baseline to 1.42 after the intervention, a reduction of more than 85% in reported UPF consumption. Compared with the usual-diet period, depression and anxiety scores were lower during the low-UPF period, with moderate to large improvements across three depression measures: the PHQ-9, the clinician-administered Montgomery-Åsberg Depression Rating Scale and the Quick Inventory of Depressive Symptomatology. Anxiety, measured on the GAD-7, improved more modestly. Participants also rated the intervention as acceptable.

Consistent results across several measures make the finding harder to dismiss as a quirk of one questionnaire, and unlike the usual nutritional epidemiology, these participants weren't sorted retrospectively by what they happened to eat. Their diets were deliberately changed.

Why This Doesn't Prove UPF Was Causing Their Depression

The study's own title gives away what is easily lost when interesting results reach the news: this was a pilot trial. Its primary purpose was to establish whether researchers could recruit people with depression who ate a lot of UPF and get them to follow a low-UPF intervention, and whether those participants found it acceptable. The symptom findings were exploratory.

The main reason for caution is that participants knew which phase they were in, since there is no practical way to disguise someone actively removing ultra-processed food from their diet. Anyone who enrols hoping to improve their health, receives guidance from researchers and knows they are on the "healthier" arm may expect to feel better, and expectation alone can move depression scores. Symptoms also fluctuate: people often enter trials when things are particularly bad, after which scores drift back towards their usual level regardless of treatment, a pattern known as regression to the mean. The crossover design helps, since half had the intervention first and the researchers accounted for period and sequence, but adjustment cannot blind people to what they are doing.

What Does Cutting UPF Change?

This is one of the central problems in ultra-processed food research: UPF is not a nutrient. The NOVA classification groups foods by the nature, extent and purpose of industrial processing, which captures soft drinks, confectionery, packaged snacks and many ready meals, while covering products with very different nutritional profiles. So when someone removes most UPF from their diet, they do not remove only processing: calories, fibre, sugar, fat, salt, additives and particular foods may all shift at once, and they may cook more or eat more regularly. In the UCSF study, participants bought and prepared their own food with guidance rather than receiving two controlled diets differing only in processing, which makes the experiment closer to real life and the mechanism much harder to identify. If depression improved because participants ate more fibre, fewer calories or a better diet overall, the trial cannot separate that from processing itself.

The Trial That Controlled the Diets

Researchers have already shown that processing level can be tested under much tighter dietary control. What they have not yet done is combine that control with a sufficiently large trial in people with depression.

The UPDATE trial, published in Nature Medicine in August 2025 by researchers at UCL and University College London Hospitals, recruited 55 adults in England with a BMI between 25 and 40 who habitually got at least half their calories from ultra-processed food. In a randomised crossover feeding trial, each participant was provided with two eight-week diets, one minimally processed and one ultra-processed, both designed to meet the UK's Eatwell Guide, and ate as much as they wanted.

Participants lost weight on both diets, but roughly twice as much on the minimally processed one. Cravings and the ability to resist them also improved about twice as much. Scaled over a year, the researchers estimated weight reductions of 13% in men and 9% in women on the minimally processed diet, against 4% and 5% on the ultra-processed one.

That is the closest anyone has come to isolating processing while holding dietary guidance constant, though it is not a perfectly matched comparison: both diets were built to meet the same recommendations, which does not mean every nutritional characteristic was identical, and critics have argued the matching was looser than the headlines implied. UPDATE also measured weight and cardiometabolic markers, not depression. What it establishes is that processing can produce different outcomes within diets following the same guidance, which makes the UCSF question worth pursuing properly.

What Do Almost Nine Million People Tell Us?

The reason a 20-person experiment matters is the size of the observational literature sitting behind it. A dose-response meta-analysis published in Family Medicine and Community Health pooled 51 prospective cohort studies involving 8,819,894 adults. For each additional 100 grams of UPF consumed per day, it reported a 14% higher risk of cardiovascular events, an 11% higher risk of hypertension, a 4% higher risk of cancer, a 3% higher risk of death from any cause and a 2% higher risk of metabolic syndrome or diabetes. Comparing the highest and lowest consumption gave 24% for cardiovascular events, 12% for cancer, 23% for overweight or obesity and 18% for all-cause mortality.

Those numbers are uncomfortable, but even 8.8 million people cannot solve the problem a 20-person experiment is designed to address. People eating the most ultra-processed food differ from those eating the least in income, education, working hours, smoking, alcohol, activity, sleep and access to fresh food. Researchers adjust for many of these, but adjustment is not randomisation, and if an unmeasured characteristic affects both UPF consumption and depression risk, part of the apparent relationship has nothing to do with processing. Causation can also run backwards, since depression affects motivation, appetite, shopping and cooking, so someone who is depressed may rely more on convenient food as a consequence of their symptoms rather than a cause.

What This Actually Means

The tempting conclusion is that people with depression should stop eating ultra-processed food. Twenty participants cannot support that, particularly as they were a specific group: middle-aged on average, mostly women, already eating large amounts of UPF and reporting at least one metabolic problem. Nor should diet be presented as a substitute for established treatment on the strength of a pilot study.

But dismissing the trial for being small would miss why it matters. The UPF debate has been dominated by observational evidence that is vast and consistent in direction, yet keeps running into the same question: are these foods causing poorer health, or standing in for something else about the people who eat them? Interventions are how that gets answered, and this one shows people with depression can substantially cut their intake in ordinary life, and that their symptom scores moved while they did. The next trial needs enough participants, a credible comparison and enough control over what people eat to see whether the improvement survives a more demanding test.

Frequently Asked Questions

Does ultra-processed food cause depression?

We don't know. Large observational studies consistently associate higher UPF consumption with depression, but they cannot establish cause. The UCSF pilot provides early experimental evidence and is far too small to settle it.

Did depression improve when people cut UPF?

In the UCSF trial, depression and anxiety scores were lower during the four-week low-UPF period than during the usual-diet period, across three depression measures. The trial included 20 participants and was not blinded.

How much ultra-processed food did participants cut?

Mean scores on the screening questionnaire fell from 10.10 to 1.42, equivalent to a reduction of more than 85%. That is a substantial dietary change rather than a modest one.

What counts as ultra-processed food?

Under the NOVA system, ultra-processed foods are industrial formulations made using processed ingredients, additives or manufacturing methods not typically used in home cooking. Examples include soft drinks, confectionery, packaged snacks and many ready-to-eat products, though nutritional quality varies considerably within the category.

Should I cut UPF if I have depression?

Eating more minimally processed food fits established healthy-eating advice, but this study does not show that removing UPF treats depression. Nobody should replace medication or therapy with dietary changes on the basis of it.

The Bottom Line

Nearly nine million people in observational studies can show that diets high in ultra-processed food travel alongside poorer health, but not why. A UK feeding trial has shown that processing level can change weight within diets following the same national guidance. And twenty people with depression have now shown that cutting UPF in ordinary life is feasible, and that their symptoms improved while they did it. That last study was too small, too short and too open to expectation and other dietary changes to tell us whether ultra-processing itself was responsible. For now the result is a reason for a larger experiment, not a new treatment, which is exactly what a good pilot study is supposed to produce.

This article is for general information and does not replace individual medical advice. If you are experiencing depression, speak to a healthcare professional rather than changing or stopping treatment on the basis of dietary research.

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Sources

• Chagwedera DN, Kim E, Chiu DT, et al. Reducing ultraprocessed foods from the diets of patients with depression: a pilot crossover trial. JAMA Psychiatry, published 23 September 2026. doi:10.1001/jamapsychiatry.2026.2320. https://jamanetwork.com/journals/jamapsychiatry/article-abstract/2854373
• Dicken SJ et al. Ultraprocessed or minimally processed diets following healthy dietary guidelines on weight and cardiometabolic health: a randomized, crossover trial. Nature Medicine 2025;31:3297–3308. https://www.nature.com/articles/s41591-025-03842-0
• UCL news release on the UPDATE trial, 4 August 2025. https://www.ucl.ac.uk/news/2025/aug/less-processed-diet-may-be-more-beneficial-weight-loss
• Liu X et al. Ultra-processed food consumption and risk of multiple chronic diseases among 8,819,894 adults from 51 prospective cohorts: a dose-response meta-analysis. Family Medicine and Community Health 2026. doi:10.1136/fmch-2026-003925
• Science Media Centre, expert reaction to the UPDATE trial, 4 August 2025. https://www.sciencemediacentre.org/expert-reaction-to-randomised-crossover-trial-of-ultra-vs-minimally-processed-foods-that-follow-healthy-diet-guidelines-and-weight-loss/