A new clinical trial led by researchers at University College London (UCL) and UCLH has found that people lose twice as much weight on a minimally processed diet compared to one based on ultra-processed foods (UPFs)—even when both diets are nutritionally identical.
Published in Nature Medicine, the study is the longest experimental trial of ultra-processed foods to date and the first to test them in real-world conditions using UK dietary guidelines.
Testing Diet Quality Beyond Nutritional Labels
The trial included 55 adults, who followed both a minimally processed food (MPF) diet and a ultra-processed food (UPF) diet, each for eight weeks, with a four-week break in between.
All meals were nutritionally matched according to the UK’s Eatwell Guide, including appropriate amounts of fat, carbohydrates, protein, fibre, salt, fruits, and vegetables. Importantly, participants were not asked to restrict calories. They were given more food than they needed and told to eat freely, as they would in their daily lives.
Dr Samuel Dicken, first author from UCL’s Centre for Obesity Research, said:
“The aim was to study how food processing—not just nutrients—impacts health outcomes like weight and body composition.”
Weight Loss Results: MPF Diet Proves More Effective
At the end of both diet periods, participants lost weight—but significantly more on the MPF diet.
- 2.06% weight loss on the minimally processed diet
- 1.05% weight loss on the ultra-processed diet
This translates to an average daily calorie deficit of:
- 290 kcal/day on the MPF diet
- 120 kcal/day on the UPF diet
These calorie deficits occurred naturally, as participants ate less despite being allowed unlimited access to food.
“Over a year, this could mean 13% weight loss in men and 9% in women with MPF, versus only 4–5% with UPF,” Dr Dicken added.
Weight Loss Came From Fat, Not Muscle
The MPF diet led to weight loss primarily from fat mass and body water, with no change in muscle mass, suggesting an overall healthier body composition.
This is important, as losing fat without losing muscle is key to sustainable weight management and long-term health.
Craving Control: A Surprising Benefit of Less Processed Food
In addition to physical health changes, the study also examined psychological responses—especially food cravings.
Participants completed questionnaires measuring craving intensity and control at several points during the study.
Compared to UPF, the MPF diet showed:
- 2x greater overall craving control
- 4x greater improvement in resisting savoury food cravings
- Nearly 2x improvement in resisting their most-craved foods
Despite losing more weight, participants felt more in control of cravings on the MPF diet—an unexpected and encouraging result.
No Significant Harm from Short-Term UPF Diet
Interestingly, the study found no significant short-term health damage from the nutritionally balanced UPF diet.
Markers like blood pressure, glucose, liver function, and cholesterol either remained stable or slightly improved—likely because the participants’ normal diets were worse than the trial’s controlled UPF version.
Still, the researchers emphasized that longer studies are needed to evaluate the true risks of UPFs beyond eight weeks.
Why Minimally Processed Foods Matter
While previous research linked ultra-processed foods to health problems, this trial provides new insight:
“Even when ultra-processed meals meet nutritional standards, they may still promote overeating and limit weight loss,” Dr Dicken noted.
The study reveals that food processing itself—not just ingredients like fat or sugar—can impact metabolism, appetite, and overall health.
Public Health Implications: Shift Focus from Individual Willpower
Professor Chris van Tulleken, a co-author, emphasized that this study challenges the idea that obesity is only about personal choice.
“The food system is built around ultra-processed products that are cheap, heavily marketed, and widely available,” he said.
“This is a public health issue, not a personal failure.”
He called for policy-level changes such as:
- Warning labels on ultra-processed foods
- Tighter marketing regulations
- Subsidies for healthy, whole foods
- Reformulation incentives for food companies
Most People Don’t Follow Nutritional Guidelines
Senior author Professor Rachel Batterham pointed out that less than 1% of UK adults follow all Eatwell Guide recommendations.
Most people follow fewer than half, and typically consume a high proportion of ultra-processed foods daily.
“Choosing more whole foods and home-cooked meals could offer additional benefits—beyond just nutrients—in improving weight and health outcomes,” she explained.
Key Takeaways from the UCL Study
✅ Minimally processed diets result in twice the weight loss compared to ultra-processed diets, even with identical nutrients
✅ Craving control improves significantly with MPF diets, helping sustain healthy habits long-term
✅ Weight loss comes from fat, not muscle, on MPF diets—supporting better overall body composition
✅ Food processing level matters as much as—or more than—nutritional content
✅ Public health strategies should focus on systemic food environment change, not just personal responsibility
Final Thoughts: Eat Whole, Not Just Healthy
This study highlights an important but often overlooked truth: how food is processed may influence weight and health as much as what’s in it.
For individuals looking to manage their weight, the message is clear—choose minimally processed foods whenever possible, even if the ingredients look similar on paper.
For policy-makers, these results strengthen the case for rethinking food environments, marketing practices, and public health campaigns to support better eating habits.