A study from University College London, published in Nature Medicine, found that adults following a minimally processed diet lost an average of 2.06% of their body weight over eight weeks, compared with 1.05% on an ultra-processed diet built around the same official dietary guidelines (Source: Dicken et al., Nature Medicine, 2025). That is roughly double, in percentage terms, but the actual difference was about one extra kilogram over two months, not a dramatic change. Both diets led to weight loss. Neither involved cutting out food groups or "eliminating" anything specific, which is the detail that got lost as the story spread online.
Who this is for
You've probably seen a version of this headline shared as "cut these foods and lose double the weight," and you want to know whether that's actually what the study found before you change how you eat. This is for anyone trying to work out how much weight a single study should carry, especially one that gets simplified into a rule as it travels.
What the research actually found
The trial, led by researchers at UCL's Centre for Obesity Research and UCL Hospital's Bariatric Centre for Weight Management and Metabolic Surgery, put 55 adults through two eight week diets in a randomised order, with a four week break in between (Source: Dicken et al., Nature Medicine, 2025). One diet was built from minimally processed ingredients, like raw meat, vegetables and oats cooked from scratch. The other used ultra-processed products, including reformulated ready meals and plant-based alternatives. Both diets followed the UK's Eatwell Guide and were matched for calories, fat, sugar and salt, so the only real difference being tested was how processed the food was.
Fifty of the 55 participants completed at least one phase. On the minimally processed diet, people naturally ate around 500 fewer calories a day than at the start, compared with around 290 fewer calories a day on the ultra-processed diet (Source: Dicken et al., Nature Medicine, 2025). Nobody was told to eat less. The researchers think the gap comes down to appetite: people on the minimally processed diet reported significantly better control over food cravings, particularly for savoury foods, and lower scores for the pull of highly palatable food (Source: Dicken et al., Nature Medicine, 2025). One of the study's authors, Dr Samuel Dicken, put the headline number in context directly: "though a 2% reduction may not seem very big, that is only over eight weeks and without people trying to actively reduce their intake" (Source: UCL News, 2025).
Why the study is more limited than the headline
This was a well designed trial by the standards of nutrition research. It randomised the order of the diets, matched both for nutrition rather than comparing "healthy" against "unhealthy" eating, and provided all the food rather than relying on people to report what they ate from memory. Independent experts who reviewed it for the Science Media Centre agreed it was a genuinely useful piece of evidence (Source: Science Media Centre, 2025).
They also pointed to real limits. With 55 participants, most of them women, the sample is too small to generalise across the whole population. The order in which people received the two diets appeared to affect the results, which is a known complication of this kind of crossover design. The study also measured a large number of outcomes without adjusting for the fact that testing more things increases the chance of finding a difference by chance, and the projected "annual" weight loss figures that circulated online were extrapolations from eight weeks of data, not something the study actually measured (Source: Science Media Centre, 2025). The researchers were candid about this too: senior author Professor Rachel Batterham noted that longer studies would be needed before drawing firm conclusions about the health markers beyond weight (Source: UCL News, 2025).
What UK health guidance actually says
Neither the NHS nor the UK government has moved to recommend eliminating ultra-processed food, and it's worth knowing that before treating this study as a new rule. The NHS is direct about it: "not all processed foods are unhealthy," and "some ultra-processed foods can be included in a healthy diet" (Source: NHS, 2026). Its advice is to eat the least healthy ultra-processed options, the ones high in saturated fat, salt or sugar, less often and in smaller amounts, rather than cutting the category out altogether.
The government's own scientific advisers have gone further, stating that more research is needed before any firm conclusion can be drawn about whether processing itself causes poor health, separately from the fact that many ultra-processed foods happen to be high in calories, fat, salt and sugar (Source: GOV.UK, 2026). "Ultra-processed" covers an enormous range of products, from a chocolate bar to a shop-bought wholegrain loaf, which is part of why a single blanket recommendation doesn't hold up well.
A UCL study published in Nature Medicine in 2025 found adults following a minimally processed diet lost an average of 2.06% of their body weight over eight weeks, compared with 1.05% on a nutritionally matched ultra-processed diet (Source: Dicken et al., Nature Medicine, 2025). The likely mechanism was appetite: people on the minimally processed diet ate around 500 fewer calories a day without being told to, compared with around 290 fewer calories a day on the ultra-processed diet (Source: Dicken et al., Nature Medicine, 2025). Independent reviewers noted the trial's small size, its mostly female sample and the order effects of its design as real limits on how far the findings can be generalised (Source: Science Media Centre, 2025). Neither the NHS nor GOV.UK currently recommends eliminating ultra-processed foods, and both point instead to moderation and the wider Eatwell Guide (Source: NHS, 2026; GOV.UK, 2026). The study is a genuine and carefully designed piece of evidence about appetite and food processing, not a case for cutting out a whole category of food.
Questions people often ask
No. The study compared two diets, both built to meet UK dietary guidelines, one from minimally processed ingredients and one from ultra-processed products. It found a difference in how much weight people lost, not a reason to cut ultra-processed food out entirely (Source: Dicken et al., Nature Medicine, 2025).
People lost an average of 2.06% of their body weight on the minimally processed diet over eight weeks, compared with 1.05% on the ultra-processed diet, a difference of roughly one kilogram over the two months (Source: Dicken et al., Nature Medicine, 2025).
Researchers think it comes down to appetite rather than willpower. People reported better control over food cravings and a lower pull toward highly palatable food on the minimally processed diet, which is thought to explain why they naturally ate fewer calories (Source: Dicken et al., Nature Medicine, 2025).
No. NHS guidance says not all processed foods are unhealthy and that some ultra-processed foods can fit into a healthy diet. It recommends eating the least healthy options less often, rather than eliminating the category (Source: NHS, 2026).
It's worth treating it as one useful piece of evidence rather than a firm rule. Independent experts pointed to its small sample size, its mostly female participants and design effects that limit how far the results generalise, and the study's own authors said longer research is needed (Source: Science Media Centre, 2025).
This article is for general information only and is not a substitute for professional medical advice. If you are concerned about a specific symptom, please see a GP or other qualified healthcare provider.