People eating minimally processed foods lost nearly twice the weight of those on ultra-processed diets, even when calories and nutrients were matched.

Eat More, Weigh Less. Why Whole Foods Are the Real Weight Loss Hack

By University College London

A new clinical trial led by researchers at UCL and UCLH found that participants lost significantly more weight when eating minimally processed foods compared to ultra-processed options. Both diets were matched for nutritional content, yet the group eating minimally processed foods lost nearly twice as much weight. The results suggest that reducing the level of food processing may offer long-term benefits for maintaining a healthy weight.

Published in Nature Medicine, the study is the first of its kind to directly compare ultra-processed foods (UPFs) and minimally processed foods (MPFs) under everyday conditions. It is also the longest experimental trial to date focused specifically on a UPF diet.^[1]

Crossover Diet Study Design: MPF vs. UPF

Researchers enrolled 55 adults and split them into two groups. One group began with an eight-week diet of minimally processed foods, including meals like overnight oats and homemade spaghetti Bolognese. After a four-week break during which participants returned to their usual eating habits, they switched to an ultra-processed food diet that included items such as ready-made lasagna and breakfast oat bars. The second group followed the same plan, but in reverse order. Of the 55 participants, 50 completed at least one full diet cycle.

Both meal plans were designed to follow the UK government’s Eatwell Guide, ensuring they were balanced in terms of fat, protein, carbohydrates, fiber, and key nutrients. Participants were given more food than they needed and were instructed to eat according to their usual appetite. No restrictions were placed on how much they could eat.

MPF Led to Greater Fat Loss and Calorie Deficit

After eight weeks on each diet, both groups lost weight, likely as a result of the improved nutritional profile of what they were eating compared to their normal diet. However, this effect was higher (2.06% reduction) on the MPF diet compared to the UPF diet (1.05% reduction)².

These changes corresponded to an estimated calorie deficit of 290 kilocalories (kcal) per day on the MPF diet, compared to 120 kcal per day on the UPF diet. To put this in context, the Eatwell Guide recommends a daily energy intake of 2,000 kcal for women and 2,500 kcal for men.

Body Composition Improved on MPF Diet

The greater weight loss experienced on the MPF diet came from reductions in fat mass and total body water, with no change in muscle or fat-free mass, indicating a healthier body composition overall.

The findings suggest that, when observing recommended dietary guidelines, choosing minimally processed foods may be more effective for losing weight.

Researchers Highlight Impact of Food Processing

Dr Samuel Dicken, first author of the study from the UCL Centre for Obesity Research and UCL Department of Behavioral Science & Health, said: “Previous research has linked ultra-processed foods with poor health outcomes. But not all ultra-processed foods are inherently unhealthy based on their nutritional profile. The main aim of this trial was to fill crucial gaps in our knowledge about the role of food processing in the context of existing dietary guidance, and how it affects health outcomes such as weight, blood pressure and body composition, as well as experiential factors like food cravings.

“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.”

MPF Significantly Reduces Food Cravings

Participants completed several questionnaires to assess their food cravings before starting the diets, and at weeks four and eight during the diets³.

There were significantly greater improvements in the number of cravings and ability to resist them (craving control) on the MPF diet compared to the UPF diet, despite greater weight loss on the MPF diet that might ordinarily be expected to lead to stronger cravings.

Craving Control Boosted on Minimally Processed Foods

On the MPF diet compared to the UPF diet, participants reported a two-fold greater improvement in overall craving control, a four-fold greater improvement in craving control for savoury food, and an almost two-fold greater improvement in resisting whichever food they most craved.

Professor Chris van Tulleken, an author of the study from UCL Division of Infection & Immunity and UCLH, said: “The global food system at the moment drives diet-related poor health and obesity, particularly because of the wide availability of cheap, unhealthy food. This study highlights the importance of ultra-processing in driving health outcomes in addition to the role of nutrients like fat, salt, and sugar. It underlines the need to shift the policy focus away from individual responsibility and onto the environmental drivers of obesity, such as the influence of multinational food companies in shaping unhealthy food environments.

Experts Call for Policy Shifts, Not Willpower

“Stakeholders across disciplines and organizations must work together and focus on wider policy actions that improve our food environment, such as warning labels, marketing restrictions, progressive taxation and subsidies, to ensure that healthy diets are affordable, available and desirable for all.”

The trial also measured secondary health markers, such as blood pressure and heart rate, as well as blood markers such as liver function, glucose, cholesterol, and inflammation. Across these markers, there were no significant negative impacts of the UPF diet, with either no change, or a significant improvement from baseline.

No Major Health Marker Differences Yet

Generally, there weren’t significant differences in these markers between the diets, and the researchers caution that longer studies would be needed to investigate these measures properly in relation to the changes in weight and fat mass.

Professor Rachel Batterham, senior author of the study from the UCL Centre for Obesity Research, said: “Despite being widely promoted, less than 1% of the UK population follows all of the recommendations in the Eatwell Guide, and most people stick to fewer than half.

Final Advice: Choose Whole Foods and Cook Fresh

“The normal diets of the trial participants tended to be outside national nutritional guidelines and included an above-average proportion of UPF, which may help to explain why switching to a trial diet consisting entirely of UPF, but that was nutritionally balanced, resulted in neutral or slightly favorable changes to some secondary health markers.

“The best advice to people would be to stick as closely to nutritional guidelines as they can by moderating overall energy intake, limiting intake of salt, sugar, and saturated fat, and prioritizing high-fiber foods such as fruits, vegetables, pulses, and nuts. Choosing less processed options such as whole foods and cooking from scratch, rather than ultra-processed, packaged foods or ready meals, is likely to offer additional benefits in terms of body weight, body composition, and overall health.”

Notes

1. MPF have undergone very little alteration from their natural state, such as fruits, vegetables, whole grains, meat, fish, and dairy products like natural yogurt. UPF have been significantly altered from their original form through processing, and typically contain ingredients not commonly used in home cooking, such as artificial flavors, preservatives, and emulsifiers.
2. Not all participants lost weight, with 10 individuals in each group gaining weight. This is thought to be due to a lack of adherence to the diet, particularly on the second diet that they undertook. When the unadjusted results from the first round of diets (either MPF or UPF) were considered in isolation, the weight loss was greater than when the average across both rounds of diets (4.09% reduction for MPF and 2.12% reduction for UPF).
3. The Control of Eating Questionnaire (CoEQ) assesses overall craving control, craving for sweet foods, craving for savory foods, positive mood, and the perceived ability to resist eating foods that are craved. The Power of Food Scale (PFS) assesses the appetite for and motivation to consume palatable foods when that food is available (but not physically present), when it is present (but not tasted), and when the food has been tasted (but not yet consumed).

Reference: “Ultraprocessed or minimally processed diets following healthy dietary guidelines on weight and cardiometabolic health: a randomized, crossover trial” by Samuel J. Dicken, Friedrich C. Jassil, Adrian Brown, Monika Kalis, Chloe Stanley, Chaniqua Ranson, Tapiwa Ruwona, Sulmaaz Qamar, Caroline Buck, Ritwika Mallik, Nausheen Hamid, Jonathan M. Bird, Alanna Brown, Benjamin Norton, Claudia A. M. Gandini Wheeler-Kingshott, Mark Hamer, Chris van Tulleken, Kevin D. Hall, Abigail Fisher, Janine Makaronidis and Rachel L. Batterham, 4 August 2025, Nature Medicine.
DOI: 10.1038/s41591-025-03842-0

This research was supported by the National Institute for Health and Care Research UCLH Biomedical Research Centre and the Rosetrees Trust.