Ultraprocessed foods (UPFs), like sugary cereals, packaged sweets, and factory-made bread, are made in labs, not kitchens. They mix food extracts with additives and industrial ingredients to create shelf-stable, flavor-packed products.
The catch? Eating lots of UPFs is linked to higher risks of obesity, heart disease, and even early death. Despite these risks, no major trial has tested their impact within official dietary guidelines. Still, countries like Brazil and groups like the WHO say: cut back on UPFs to protect your health.
In the longest-ever real-world trial of its kind, UCL researchers pitted UPFs against minimally processed foods (MPFs), with both diets matched for nutrients.
The result? People on the MPF diet lost twice as much weight as those on the UPF diet. The takeaway: Even when calories and nutrients are equal, less processing may mean more progress toward a healthy weight.
New study sheds light on reducing ultra-processed food intake
In a groundbreaking study, 55 adults were split into two groups and fed two different diets: minimally processed foods (MPF) like overnight oats and homemade Bolognese, and UPF like oat bars and ready-made lasagne.
After 8 weeks on one diet, participants had a 4-week break before switching to the other. Meals were delivered to their homes, matched to the UKs Eatwell Guide for nutrients, and participants could eat freely, with no calorie limits, just natural appetite.
Key twist: Despite equal nutrition, people lost more weight on the MPF diet, hinting that how food is made matters as much as whats in it.
After eight weeks on each diet, participants in both groups lost weight, likely due to the improved nutritional quality compared to their usual eating habits. However, the effect was more pronounced on the MPF diet, which led to a 2.06% reduction in body weight, compared to a 1.05% reduction on the UPF diet.
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This difference translated into an estimated daily calorie deficit of 290 kilocalories on the MPF diet versus 120 kilocalories on the UPF diet. For context, the UKs Eatwell Guide recommends a daily intake of 2,000 kcal for women and 2,500 kcal for men.
Importantly, the greater weight loss on the MPF diet came from reductions in fat mass and total body water, with no loss of muscle or fat-free mass, indicating a healthier shift in body composition.
The findings suggest that, when observing recommended dietary guidelines, choosing minimally processed foods may be more effective for losing weight.
Dr Samuel Dicken, first author of the study from the UCL Centre for Obesity Research and UCL Department of Behavioural 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.
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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. Although a 2% reduction may seem insignificant, it represents a significant decrease over just eight weeks, especially when people are not actively trying to reduce their intake. If we scaled these results up over a year, wed 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.
Participants completed a series of questionnaires to evaluate their food cravings before beginning the diets, and again at weeks four and eight during the intervention. Despite experiencing greater weight loss, which typically intensifies cravings, those on the MPF diet showed significantly more substantial improvements in both the frequency of cravings and their ability to resist them, compared to those on the UPF diet.
Specifically, the MPF group demonstrated a two-fold greater improvement in overall craving control, a four-fold greater improvement in resisting savoury food cravings, and nearly double the improvement in resisting their most craved foods.
This study shows that its not just whats in our food, like fat, salt, and sugar, but how its made that affects our health. Its a wake-up call to rethink the blame game: instead of pointing fingers at individuals, we need to look at the bigger picture. Giant food companies play a huge role in crafting environments full of unhealthy choices, and thats where policy needs to step in.
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Stakeholders across disciplines and organisations 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 looked at other health indicators like blood pressure, heart rate, and blood markers for liver function, glucose, cholesterol, and inflammation. Surprisingly, the UPF diet didnt show any harmful effects on these markers; some even improved slightly or stayed the same.
However, when comparing the UPF and MPF diets, there were no significant differences in these areas. Researchers emphasize that these results are just a snapshot, and longer-term studies are needed to truly understand how these diets affect deeper health outcomes beyond weight and fat loss.
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.
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The regular 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 favourable 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 prioritising high-fibre 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.
Journal Reference:
- Dicken, S.J., Jassil, F.C., Brown, A. et al. Ultraprocessed or minimally processed diets following healthy dietary guidelines on weight and cardiometabolic health: a randomized, crossover trial. Nat Med (2025). DOI: 10.1038/s41591-025-03842-0
