Can You Lose More Weight Eating the Same Calories-Just Less Processed? Study Sheds Light - Video
Overview
A new clinical trial led by researchers from University College London (UCL) and UCL Hospitals has found that participants following a minimally processed diet lost twice as much weight as those consuming ultra-processed foods-even when both diets were nutritionally matched. The study, published in Nature Medicine, is the first of its kind to compare ultra-processed (UPF) and minimally processed (MPF) diets under real-world conditions and is also the longest experimental study of a UPF diet to date.
The research involved 55 adults divided into two groups. One group began with an eight-week MPF diet consisting of meals like homemade spaghetti Bolognese or overnight oats, followed by a four-week break and then an eight-week UPF diet that included ready meals like lasagna or packaged oat bars. The other group followed the reverse order. Participants received more food than needed and were allowed to eat freely. Participants completed several questionnaires to assess their food cravings before starting the diets, and at weeks four and eight during the diets.
Despite both diets being designed to meet the UK government’s Eatwell Guide in terms of calories, fat, salt, and fibre, weight loss was significantly higher on the MPF diet.
Participants on the MPF diet lost an average of 2.06% of their body weight, compared to just 1.05% on the UPF diet. The MPF group also experienced greater reductions in fat mass and total body water, while maintaining muscle mass—indicating healthier body composition.
The MPF diet also improved participants' ability to resist cravings, particularly for savoury foods.
"The primary outcome of the trial was to assess percentage changes in weight, and on both diets, we saw a significant reduction, but the effect was nearly double on the minimally processed diet. Though a 2% reduction may not seem very big, that is only over eight weeks and without people trying to actively reduce their intake. If we scaled these results up over the course of a year, we'd expect to see a 13% weight reduction in men and a 9% reduction in women on the minimally processed diet, but only a 4% weight reduction in men and 5% in women after the ultra-processed diet. Over time this would start to become a big difference," said Dr. Samuel Dicken, first author of the study from the UCL Centre for Obesity Research and UCL Department of Behavioural Science & Health.
Though the trial found no significant negative effects from the UPF diet on blood markers, experts stress the long-term benefits of reducing food processing.
Reference: Dicken, S. J., et al. (2025). Ultraprocessed or minimally processed diets following healthy dietary guidelines on weight and cardiometabolic health: a randomized, crossover trial. Nature Medicine. doi.org/10.1038/s41591-025-03842-0.
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