A new study has found that people can lose more weight by eating less processed food, even when the meals have the same nutrients.
Researchers from University College London (UCL) and University College London Hospitals (UCLH) discovered that participants lost about twice as much weight eating minimally processed foods compared to ultra-processed foods.
The study, published in Nature Medicine, is the first long-term trial to compare the two diets in everyday conditions.
It involved 55 adults who tried each diet for eight weeks, separated by a four-week break.
One diet focused on minimally processed meals such as overnight oats or homemade spaghetti Bolognese.
The other consisted of ultra-processed options like packaged breakfast bars or ready-made lasagna.
Importantly, both diets were nutritionally matched. They followed the UK’s Eatwell Guide, meaning they had similar amounts of fat, sugar, protein, carbohydrates, fiber, salt, and fruits and vegetables.
Participants had more food delivered than they needed and were told to eat as much or as little as they liked—no calorie restrictions.
On both diets, participants lost some weight, likely because the trial food was healthier than their normal eating habits.
But the difference was clear: people lost an average of 2.06% of their body weight on the minimally processed diet, compared to 1.05% on the ultra-processed one. This worked out to a daily calorie deficit of about 290 calories for the minimally processed diet versus 120 calories for the ultra-processed diet.
The weight loss on the minimally processed diet came mainly from fat, without losing muscle mass—suggesting a healthier body composition.
Researchers estimated that if these results continued for a year, men could lose around 13% of their body weight and women about 9% on the minimally processed diet, compared to only 4–5% on the ultra-processed diet.
Interestingly, the minimally processed diet also reduced food cravings more effectively. Participants reported twice the improvement in controlling cravings overall, four times the improvement for savory cravings, and nearly double the ability to resist their most tempting foods.
While some health markers such as blood pressure and cholesterol didn’t show big differences between the diets over the short term, researchers say longer studies are needed to see the full impact.
The findings suggest that focusing only on nutrients like fat, sugar, and salt isn’t enough—how much a food is processed also matters for health and weight control. Ultra-processed foods are common in modern diets because they are cheap, convenient, and heavily marketed.
Professor Chris van Tulleken, one of the study’s authors, said that governments and communities need to address the food environment, not just individual choices. This could include measures like warning labels, advertising restrictions, taxes on unhealthy foods, and subsidies for healthier options.
Professor Rachel Batterham, senior author of the study, said the best approach for individuals is to follow nutritional guidelines as closely as possible, limit salt, sugar, and saturated fat, and eat plenty of high-fiber foods.
Cooking from scratch and choosing whole, minimally processed ingredients is likely to bring extra benefits for weight, body composition, and overall health.
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