A University of California team in San Francisco, United States, has called for large-scale tests to confirm a connection between a junk food habit and vulnerability to depression after 20 patients reported improved symptoms, such as reduced anxiety, after switching to a healthier diet.
The participants in the preliminary investigation “reduced ultra-processed food intake by more than 85%”, and in turn reported “moderate to large improvements across three measures of depression”, the university stated.
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The tests “successfully established the viability of carrying out this research in a larger-scale trial”, said study senior author and Ray and Dagmar Dolby Distinguished Professor in Psychiatry and Neurology Dr Andrew Krystal.
Published in JAMA Psychiatry, an American Medical Association journal, the paper was described by the university as possibly “the first to compare symptoms in people with depression before and after they switched from their regular ultra-processed diet to healthier food”.
In their paper, the team explained that “further studies are needed” to assess how factors such as a “change in macronutrient content”, such as sugar and fat, affects depression patients, as well as how calorie intake differences play out.
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The researchers added that the impact of “contaminants from processing”, and the mix of additives, preservatives, stabilisers, artificial colours and flavourings, should be assessed in future examinations.
As well as being convenient, quick to cook and often less expensive than healthier options, ultra-processed snacks can trigger dopamine, sometimes called the pleasure hormone, said study lead author and assistant professor of psychiatry Dr D. Nyasha Chagwedera.
The implication is that junk food “may harm your gut in ways that ripple up to your brain”, according to her.
The findings follow multiple research papers pointing to a link between gut and mental health, in turn suggesting diet could be a factor in how people feel and think.
In April (2026), a team of Vienna-based doctors in Austria published research linking diet and stress after researchers in Singapore reached similar findings last year (2025). – dpa
