A diet based on minimally processed foods (MPF) leads to significantly greater weight and fat loss compared to an ultraprocessed food (UPF) diet, even when both diets are designed to meet national healthy eating recommendations, according to findings from the UPDATE trial.¹

The consumption of UPF—industrial formulations combining food extracts with additives—has been linked to increased risks of obesity and cardiometabolic disease.² However, until now, no randomised controlled trial had assessed the health impact of food processing within the context of national dietary guidelines. The UPDATE (Ultra processed versus minimally processed diets following UK dietary guidance on health outcomes) trial aimed to address this evidence gap.

UPDATE was a randomised, 2x2 crossover controlled feeding trial conducted in England. The study enrolled 55 adults with overweight or obesity (body mass index [BMI] ≥25 to <40 kg/m²) whose habitual diet consisted of at least 50% UPF.

Participants were provided with two distinct 8-week ad libitum diets in a random order, separated by a 4-week washout period. One diet was composed of MPF, while the other consisted of UPF. Crucially, both diets were designed to adhere to the UK's Eatwell Guide recommendations for macronutrients and food groups. The primary endpoint was the within-participant difference in percentage weight change (%WC) from baseline to week 8.

After 8 weeks, participants lost weight on both diets. However, the weight loss was significantly greater on the MPF diet compared to the UPF diet (−2.06% vs −1.05%, respectively; Δ%WC: −1.01%; P=0.024).

This greater weight loss was primarily driven by a reduction in fat mass. The MPF diet resulted in significantly greater reductions in absolute weight (−0.96 kg; P=0.019), BMI (−0.34 kg/m²; P=0.021), fat mass (−0.98 kg; P=0.004), and triglycerides (−0.25 mmol/l; P=0.004) compared to the UPF diet. Conversely, the UPF diet was associated with a significantly greater reduction in LDL-cholesterol (0.25 mmol/l; P=0.016). Mild gastrointestinal adverse events were common with both diets, with no related serious adverse events reported.

These findings demonstrate that the level of food processing has a significant impact on weight and body composition, independent of the nutritional profile as defined by national guidelines. The study highlights that while following a 'healthy' UPF diet can lead to weight loss compared to a typical Western diet, a 'healthy' MPF diet yields superior results, particularly for reducing adiposity. The authors concluded that their “findings indicate greater weight loss on MPF than UPF diets and needing dietary guidance on food processing in addition to existing recommendations.”¹

Results from a follow-up 6-month behavioural support programme are expected to be reported separately.

References

1. Dicken SJ, Jassil FC, 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. https://doi.org/10.1038/s41591-025-03842-0

2. Hall KD, Ayuketah A, Brychta R, et al. Ultra-processed diets cause excess calorie intake and weight gain: an inpatient randomized controlled trial of ad libitum food intake. Cell Metab 2019;30:67–77. https://doi.org/10.1016/j.cmet.2019.05.008

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