Public health advice has long focused on nutrients: eat less sugar and salt, more fiber, balance fats and carbohydrates. But a new clinical trial shows that how food is processed may shape health outcomes just as much as what nutrients it contains.
In a randomized crossover trial published in Nature Medicine, researchers tested two diets that both met the UK’s official Eatwell Guide. One diet was built entirely from minimally processed foods (MPF), while the other relied on nutritionally improved, reformulated ultra-processed foods (UPF) — the packaged cereals, ready meals and plant-based alternatives that dominate supermarket shelves.
The results showed that both groups lost weight over eight weeks, but the MPF diet led to significantly greater reductions in body weight and fat mass. Participants on the MPF plan also reported better control over cravings and greater improvements in triglyceride levels. Meanwhile, the UPF diet showed some benefits — including modest reductions in LDL cholesterol and fasting glucose — but did not reduce body fat in the same way.
This challenges a common assumption: that if a food is reformulated to fit nutrient guidelines, it is automatically as healthy as its less processed counterpart. As the trial revealed, even “healthy” UPFs were more energy-dense and encouraged different eating behaviors than meals made from basic ingredients. Side effects such as fatigue, constipation and reflux were also more frequent on the UPF diet.
The implications are broad. Nutrition policy has historically emphasized reformulation and labeling — salt targets, sugar taxes and front-of-pack health claims. These tools are valuable, but they may not be enough. The findings suggest that food processing itself deserves a place in dietary guidelines.
The study also shows that a successful approach to improve nutrition policy should go beyond individual willpower or nutrient counting. It means reshaping the food environment so that healthier, minimally processed foods are more accessible, affordable, and appealing than their ultra-processed alternatives. The authors suggest some measures to enforce system-level changes. For example, governments could support subsidies for fruit, vegetables, and staple foods, while limiting the dominance of UPF in marketing and retail spaces. Communities, too, can play a role — through local food initiatives, cooking education, and advocacy for better choices in schools and workplaces.
In short, this study adds weight to what public health experts have long suspected: not all calories are created equal, and the industrial design of food matters. Reducing reliance on ultra-processed foods, even when they meet nutrient targets, could be key to addressing obesity and improving long-term health.
Coordinator at la Verneda-Sant Martí Learning Community and adjunct professor at the University of Barcelona