A new clinical trial led by researchers at University College London (UCL) has shown that people lose nearly twice as much weight when they eat minimally processed foods compared to ultra-processed ones, even when the two diets have the same nutrients.
The study, published in the journal Nature Medicine, is the first to test the effects of food processing in a real-world setting over a long period.
Ultra-processed foods (UPFs) include items like packaged snacks, ready meals, and sugary drinks, while minimally processed foods (MPFs) include things like homemade meals, fresh fruits and vegetables, and whole grains.
The trial involved 55 adults who were randomly assigned to start with either an eight-week diet of MPF or UPF. After a four-week break where participants went back to their regular eating habits, they switched diets. In total, 50 people completed at least one of the diets.
Importantly, both diets were designed to match the UK’s healthy eating guidelines. The meals included similar levels of fat, protein, carbohydrates, salt, and fiber. Participants were provided with more food than they needed and were allowed to eat as much or as little as they wanted. They were not told to restrict their intake.
Even though both groups lost weight after eight weeks, the group on the minimally processed diet lost nearly twice as much weight.
On average, they had a 2.06% reduction in body weight, while the ultra-processed group had a 1.05% reduction. This difference was equal to about 290 fewer calories per day on the MPF diet, compared to 120 fewer calories on the UPF diet.
The weight loss from the MPF diet came mostly from fat mass and water, rather than muscle, which suggests a healthier change in body composition. The findings suggest that eating less processed foods could be a more effective way to maintain a healthy weight over the long term.
Dr. Samuel Dicken, the first author of the study, explained that although some ultra-processed foods might not look unhealthy based on nutrition labels, how they are made still matters. This study fills an important gap in understanding how food processing, even when nutrients are controlled, can affect weight, blood pressure, and food cravings.
Participants also completed surveys about their cravings throughout the study. Those on the minimally processed diet reported much better control over cravings. They were better able to resist cravings overall, especially for savory foods, and showed a much stronger ability to avoid the foods they craved most.
Professor Chris van Tulleken, another author, said the study shows how powerful the food environment is in shaping health.
He emphasized the need for policy changes that make healthy foods easier to access, more affordable, and more appealing. Instead of just focusing on personal choices, he said, efforts should target the way food companies promote and sell ultra-processed foods.
The researchers also measured other health markers like blood pressure, heart rate, and blood test results. They found no major negative changes with either diet, but they also note that longer studies would be needed to fully understand the effects on long-term health.
Professor Rachel Batterham, senior author of the study, pointed out that most people in the UK don’t follow all of the national healthy eating guidelines.
The trial diets were healthier than what participants usually ate, which may explain why even the ultra-processed diet in the study didn’t cause harm. Still, she said the best advice is to follow the nutrition guidelines as closely as possible, eat more fiber-rich whole foods, and limit processed items when possible.
This study was supported by the National Institute for Health and Care Research UCLH Biomedical Research Centre and the Rosetrees Trust.
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The study is published in Nature Medicine.
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