A new clinical trial from University College London (UCL) and University College London Hospitals (UCLH) has found that eating minimally processed foods helps people lose twice as much weight as eating ultra-processed foods, even when the two diets are nutritionally identical.
This suggests that simply cutting down on food processing could support long-term healthy weight management.
The study, published in the journal Nature Medicine, is the longest and most realistic experiment comparing ultra-processed food (UPF) with minimally processed food (MPF) diets. It involved 55 adults who each followed both diets during different periods.
One group started with an eight-week MPF diet, featuring meals like overnight oats and homemade spaghetti Bolognese. After a four-week break, they switched to an eight-week UPF diet, which included ready-made meals and processed snacks. The other group did the opposite.
Importantly, both diets matched the UK’s official Eatwell Guide recommendations in terms of calories, fat, protein, fibre, and other nutrients. Participants received more food than they needed and were allowed to eat freely. No one was told to limit their food intake.
Both diets led to weight loss, but the MPF diet produced nearly double the results—a 2.06% body weight reduction versus just 1.05% on the UPF diet. This translates to an estimated daily calorie deficit of 290 kcal on the MPF diet compared to only 120 kcal on the UPF diet.
Over time, this difference could be significant. Researchers estimate that after one year, the MPF diet could result in a 13% weight loss in men and 9% in women, compared to 4% and 5% respectively on the UPF diet.
The extra weight loss from the MPF diet was mostly due to a drop in fat and water, not muscle mass, suggesting healthier changes in body composition. Participants also reported fewer food cravings on the MPF diet, especially for savoury foods.
Improvements in their ability to resist cravings were two to four times greater compared to when they were on the UPF diet.
Lead author Dr. Samuel Dicken explained that although UPF can sometimes meet nutrition standards, the level of processing may still affect weight and health outcomes.
Professor Chris van Tulleken added that global food systems often promote unhealthy diets by flooding the market with cheap, ultra-processed products. He emphasized the need for policies that make healthy foods more accessible and appealing.
The study also tracked health measures such as blood pressure, cholesterol, and blood sugar. No harmful effects were found from the UPF diet, and some health markers even improved slightly. However, researchers caution that longer-term studies are needed to fully understand these effects.
Professor Rachel Batterham, a senior researcher on the project, noted that very few people in the UK actually follow all Eatwell Guide recommendations. Most participants in the study had unhealthy eating habits before joining, which may explain why switching to even a balanced UPF diet led to some health improvements.
Still, she recommends choosing whole foods and cooking at home when possible, as minimally processed meals appear to be better for both weight control and overall health.
The study was supported by the National Institute for Health and Care Research UCLH Biomedical Research Centre and the Rosetrees Trust.
If you care about health, please read studies about why beetroot juice could help lower blood pressure in older adults, and potassium may be key to lowering blood pressure.
For more health information, please see recent studies about rosemary compound that could fight Alzheimer’s disease, and too much of this vitamin B may harm heart health.
The study is published in Nature Medicine.
Copyright © 2025 Knowridge Science Report. All rights reserved.
