Ultra-processed food diets may be less effective for weight loss and reducing cardiometabolic disease risk than minimally processed diets, even when both follow the same national dietary guidelines, according to research published in Nature Medicine. The findings, based on a community-level clinical trial involving 55 adults in England, suggest that the degree of food processing may play a role in shaping certain health outcomes, beyond overall nutritional composition.

Global consumption of ultra-processed foods has risen sharply in recent decades, coinciding with increasing rates of obesity and chronic conditions, such as type 2 diabetes and cardiovascular disease. In the UK, over 50% of food consumed is reported to be ultra-processed, with similar consumption levels in the USA and Europe. Examples include breakfast cereals, sweets, and mass-produced bread. Although numerous studies have consistently linked high intake of ultra-processed foods to increased risks of adverse health outcomes, these data are often limited by confounding factors and cannot establish causality.

Samuel Dicken and colleagues conducted a randomised crossover trial comparing diets heavy in ultra-processed food versus those with minimally processed food, both structured around the UK Eatwell Guide — a set of national dietary recommendations that promote healthy and balanced nutrition. The trial involved 55 adults who received either pre-prepared ultra-processed foods, such as breakfast cereals or lasagna ready meals, or pre-prepared minimally processed foods, such as overnight oats or homemade spaghetti bolognese, delivered to their home over an 8-week period. After a 4-week break, participants switched to the alternative diet for another 8 weeks, which allowed for within-participant comparisons of the effect of MPF and UPF diets over the course of 6 months. In total, 50 participants completed at least one diet.

The authors found that both diets following the Eatwell guidelines led to significant weight loss over the course of 8 weeks. However, the minimally processed food diet resulted in a 2% average reduction in weight, compared with 1% for the ultra-processed diet. Beyond weight reductions, the minimally processed diet was more effective in improving body composition related to cardiometabolic health measures, such as reducing fat mass, visceral fat and triglyceride levels (although low-density lipoprotein cholesterol was lower after the UPF diet). Although overall diet satisfaction ratings did not differ significantly, participants rated the flavour and taste of the ultra-processed diet higher than the minimally processed diet. Overall self-reported food craving control was significantly improved with the MPF diet compared with UPF diet, which may have helped to support the lower calorie consumption leading to the greater weight loss observed on the MPF diet.

The findings suggest that even within healthy dietary guidelines, the degree of food processing has a role in weight management and cardiometabolic health. The authors acknowledge that people with dietary restrictions (such as vegan, halal and kosher diets) were not included.