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Concerns over conclusions in an ultra-processed food trial

Nature Medicine (2026)Cite this article

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Matters Arising to this article was published on 06 January 2026

The Original Article was published on 04 August 2025

arising from S. J. Dicken et al. Nature Medicine https://doi.org/10.1038/s41591-025-03842-0 (2025)

Although extensive observational data link consumption of ultra-processed food (UPF; as defined by the Nova classification system) to obesity and other chronic health conditions, few interventional studies on this question have been conducted. Aiming to fill this knowledge gap, Dicken et al.1 compared an UPF diet to a minimally processed food (MPF) diet in 55 adults with a high body mass index (BMI), using a 2-by-2 crossover design with 8-week diet arms and a 4-week washout period. In their calculation of the primary outcome, an ‘intention-to-treat’ (ITT) mixed-effects model adjusted for several covariates, percentage weight loss was greater on the MPF-versus-UPF diet (−2.06% versus −1.05%, P = 0.024), amounting to a ~1-kg difference. The authors proposed that these data extrapolate at 1 year to 9–13% versus 4–5% weight loss, respectively. However, conservative interpretation of the data indicates that any marginal benefit of their MPF-versus-UPF diet would have limited public health importance and that the findings do not support their call for incorporation of “dietary guidance on food processing in addition to existing recommendations”1.

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Authors and Affiliations

  1. New Balance Foundation Obesity Prevention Center, Boston Children’s Hospital, Boston, MA, USA

    David S. Ludwig

  2. Department of Pediatrics, Harvard Medical School, Boston, MA, USA

    David S. Ludwig

  3. Department of Nutrition, Harvard TH Chan School of Public Health, Boston, MA, USA

    David S. Ludwig & Walter C. Willett

  4. Steno Diabetes Center Copenhagen, Herlev, Denmark

    David S. Ludwig

  5. Department of Biostatistics, Epidemiology, and Informatics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA

    Mary E. Putt

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  1. David S. Ludwig
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  2. Walter C. Willett
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All authors contributed to the writing of this paper and read and approved the final version.

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Correspondence to David S. Ludwig.

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Competing interests

D.S.L. received royalties for books on obesity and nutrition. The other authors declare no competing interests.

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Ludwig, D.S., Willett, W.C. & Putt, M.E. Concerns over conclusions in an ultra-processed food trial. Nat Med (2026). https://doi.org/10.1038/s41591-025-04087-7

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