How the trial worked
Published in Nature Medicine in 2025, UPDATE randomised 55 adults in England to two diet sequences: minimally processed and ultraprocessed, eight weeks each. Both followed the Eatwell Guide and food was provided. The intention-to-treat analysis included 50 people; 43 completed both diets.
The main result
Estimated average weight change was −2.06% on the minimally processed diet and −1.05% on the ultraprocessed diet, a statistically significant difference. Both produced weight loss. Claiming that any diet containing ultraprocessed food necessarily causes weight gain would therefore misrepresent this experiment.
Important limitations
The sample was small and mostly female, with eight-week diet periods. Diet-order effects were observed; energy density and other features differed. The trial does not isolate a particular additive or measure years of disease risk. An average result cannot predict an individual response.
Using the research while shopping
Consider processing alongside ingredients, fibre, salt, cost and convenience. A processing category alone does not describe a whole meal’s quality. Compare realistic options that fit your week. Turning one scientific headline into a forbidden-food list loses the context that makes the research useful.
