August 4, 2025

Ultra-processed versus minimally processed diets (that follow healthy diet guidelines) and weight loss – a randomised, crossover trial

Scientists at UCL have carried out a randomised, crossover trial to compare weight change on UPF (ultra-processed foods) versus MPF (minimally processed foods) when diets in both cases adhered to healthy diet guidelines.

This is the first RCT of UPF carried out in real world conditions (participants were at home rather than living in a lab/hospital during the trial) and is also longer in duration than previous RCTs on UPF.

There were 55 participants in the trial – half started with a UPF diet and (following a ‘wash out’ period) switched to an MPF diet, and the other half did vice versa. Participants were provided with ad lib food, and the two diets were nutritionally matched and both diets adhered to the Eatwell Guide for levels of fat, saturated fat, protein, carbohydrate, salt and fibre, and quantities of fruits and veg.

Weight change in the individual participants was the primary outcome of the trial. The paper was published in Nature Medicine.

Journalists came to this press briefing to hear the results from the scientists who’ve run the trial, and to ask your questions.

Speakers included:

Dr Samuel Dicken, Research Fellow at the Department of Behavioural Science and Health, and at the Centre for Obesity Research, UCL

Dr Adrian Brown, NIHR Advanced Fellow and Senior Research Fellow in Nutrition and Dietetics and Senior Specialist Dietitian at the Centre of Obesity Research, UCL

Dr Friedrich Jassil, Research Fellow at the Service of Endocrinology, Diabetology and Metabolism, University of Geneva; and Honorary Research Fellow at the Centre for Obesity Research, UCL

This Briefing was accompanied by an SMC Roundup of comments.