Both groups ate meals designed to hit the same calories, protein, fat and carbs on paper. Yet the group living on home-cooked, minimally processed food lost roughly twice as much weight as the group eating nutritionally matched ultra-processed alternatives.
The finding comes from a University College London trial published in Nature Medicine in August 2025. Fifty adults completed at least one arm of an eight-week crossover comparing a minimally processed diet with an ultra-processed one, both built to the UK Eatwell Guide.
Participants weren't dieting. They had more food than they needed delivered to their homes and were free to eat as much or as little as they wanted, the researchers wrote. No calorie targets, no portion policing.
Over eight weeks, people lost 2.06% of their body weight on the minimally processed diet, compared with 1.05% on the ultra-processed one, the research team reported. The gap traced back to how much people actually ate.
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The calorie deficit showed up on its own
Without being told to cut back, participants ran a 290 kcal/day deficit on the minimally processed diet, versus 120 kcal/day on the ultra-processed one, according to the same report. Same nutrient targets, different eating behavior.
The researchers described the study as the first interventional trial to compare ultra-processed and minimally processed diets in real-world conditions, and the longest experimental study of an ultra-processed diet so far. Diet order was randomized, with a four-week washout in between when people returned to their normal eating.
Meals on the minimally processed arm looked like overnight oats or homemade spaghetti Bolognese. On the ultra-processed arm, a breakfast oat bar or a lasagne ready meal. Same food group on paper, different level of industrial processing on the plate.
Cravings dropped and muscle held
Cravings shifted in the same direction as the scale. Participants reported roughly twice the improvement in overall craving control on the minimally processed diet, and about four times the improvement in cravings for savory foods.
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Body composition told a similar story. The weight lost on the minimally processed diet came from fat and body water, with no significant drop in muscle. Blood pressure, blood glucose, cholesterol and liver markers were broadly similar across the two arms over eight weeks.
What a year might look like
Projected forward, the weekly rate of loss adds up. If the trial's pattern held for 12 months, men on the minimally processed diet would lose about 13% of their body weight and women about 9%, first author Dr. Samuel Dicken said. On the ultra-processed diet, the projected reductions were roughly 4% in men and 5% in women.
Those figures are extrapolations from an eight-week trial, not a promise. But the direction lines up with a growing pile of research pointing at food processing itself, not just fat, salt and sugar counts, as a driver of overeating.
"This study highlights the importance of ultra-processing in driving health outcomes in addition to the role of nutrients like fat, salt and sugar," said Professor Chris van Tulleken, one of the study's authors.
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Senior author Professor Rachel Batterham framed the practical takeaway around existing guidance: moderate calories, limit salt, sugar and saturated fat, prioritize high-fiber foods. "Choosing less processed options such as whole foods and cooking from scratch, rather than ultra-processed, packaged foods or ready meals, is likely to offer additional benefits in terms of body weight, body composition and overall health," she said.
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This article is made and published by Jesper Bengtson, who may have used AI in the preparation.