New Study Finds Minimally Processed Diets Lead to Greater Weight Loss—Even When Following National Guidelines

By Prof. Nelly Pitteloud | August 2025

Research in Brief

A new clinical trial from the UK is challenging what we thought we knew about healthy eating. The UPDATE trial (Ultra Processed versus Minimally Processed Diets following UK dietary guidance on health outcomes) published in Nature Medicine is the first study to examine the health effects of ultraprocessed vs. minimally processed diets while still aligning with the UK’s Eatwell Guide—the country's official recommendations for healthy eating.

Key points

Conducted in a diverse group of adults with overweight or obesity, the study offers the most rigorous evidence to date that minimally processed foods offer real metabolic advantages—even when nutrient content is kept consistent. Despite similar calories and nutrients, the MPF diet led to greater weight loss, better fat reduction, and improved appetite control.

Why it matters

Even when following the rules, what’s done to your food matters. Processing, not just content, may shape how your body responds. 

What’s the Big Question?

For years, researchers have warned about the rise of ultraprocessed foods (UPFs)—industrially made foods containing added sugars, oils, refined starches, artificial additives, and very little whole food. However, most sudies have been observational—they could show associations, but not causation.

In the UK, UPFs now make up more than 50% of daily energy intake, a trend mirrored in the US and many other countries.

But so far, national dietary guidelines—including the UK’s Eatwell Guide—don’t specifically mention food processing. They focus on nutrients (fat, protein, carbs) and food groups (fruits, dairy, grains), without addressing the level of processing.

With obesity and chronic disease rates rising, the UPDATE study asked: If we compare two diets that meet the same national recommendations, but one uses whole foods and the other uses UPFs—will health outcomes differ?

What Did the Study Test?

Researchers designed two diets that followed the UK’s Eatwell Guide—the country's official nutrition framework—with healthy levels of fat, sugar, salt, and fiber. The only difference between the diets? The level of food processing.

• The Minimally Processed Diet featured meals like overnight oats, plain yogurt, and scratch-made spaghetti Bolognese.

• The Ultraprocessed Diet included foods like flavored yogurt, frozen lasagna, plant-based milks, and whole-grain breakfast cereals.

All meals were provided by the researchers, and participants could eat as much or as little as they wanted.

Fifty-five adults with overweight or obesity who typically consumed over 50% of their calories from ultraprocessed foods —a figure common in the UK and many other Western nations were recruited.

In a crossover trial design, participants followed each diet (MPF and UPF) for 8 weeks, with a break in between. Importantly, both diets aligned with the macronutrient and food group recommendations of the Eatwell Guide—they only differed in the level of processing. The only real difference? The degree of processing.

Foods were brought by the researchers. Participants were allowed to eat as much as they wanted—there were no calorie restrictions or portion controls. This “ad libitum” design helped the researchers evaluate how the diets naturally influenced hunger, fullness, and eating behavior in real-life conditions.

What Were the Results?

More Weight Loss & Greater Fat Reduction - Without counting Calories

The results were striking. Both diets—ultraprocessed and minimally processed—led to modest weight loss, but participants shed significantly more weight on the minimally processed (MPF) diet: about 2% of their body weight, compared to just 1% on the ultraprocessed (UPF) diet. That difference, while seemingly small, was statistically significant and consistent across individuals.

What’s especially notable is that no calorie limits were imposed. Participants ate as much as they wanted, suggesting that the type of food—not just the nutrients—impacts how much we eat. Factors like texture, fiber, energy density, and satiety cues likely played a role in curbing intake naturally on the MPF diet.

But weight is just one part of the story. Body composition—what that weight is made of—also improved more on the minimally processed plan. Participants experienced greater reductions in total fat mass, body fat percentage, and visceral fat (the deeper abdominal fat linked to insulin resistance and heart disease). Meanwhile, muscle and bone mass stayed stable, showing that fat—not lean tissue—was primarily lost.

In other words: less processed, more powerful.

Appetite and Cravings: Less Processed, More Control

One of the more intriguing findings came from subjective appetite ratings. Participants felt more in control of their cravings, particularly for sweet and savory foods, while eating MPD. They also found it easier to resist tempting foods, and experienced fewer intrusive food thoughts—something that could make a meaningful difference for anyone trying to maintain a healthy eating pattern over time.

While total calorie intake wasn’t measured (it was an ad libitum, or "eat as much as you want" model), appetite cues and satiety seemed to improve when people ate whole, less processed foods.

What About Blood Markers?

• Triglycerides decreased more on the MPF diet.

• Interestingly, LDL cholesterol decreased more on the UPF diet—possibly due to formulation differences in packaged food items.

• Other markers like glucose, HbA1c, and cholesterol improved on both diets, but most changes were more favorable on the MPF diet.

These results suggest that food processing may affect metabolic health through mechanisms not entirely explained by macronutrients or food groups alone. The way foods are broken down, combined, and reformulated in industrial processing may interact with digestion, absorption, the gut microbiome, and appetite regulation in ways we're only beginning to understand.

Why Does This Matter?

Until now, most national dietary guidelines—like the UK Eatwell Guide or the U.S. Dietary Guidelines—have focused on what we eat: recommending more fruits and vegetables, whole grains, healthy fats, and fiber. But how those foods are made—the level of industrial processing they undergo—has largely been left out of the conversation.

That’s where the UPDATE trial breaks new ground.

By directly comparing two diets with similar nutrient profiles, both built around official healthy eating recommendations, but differing only in degree of food processing, the researchers showed that processing level has a real, measurable impact:

• The minimally processed diet led to more weight loss, greater reductions in body fat, and better appetite regulation, even without calorie restrictions.

  
  

In an era when ultraprocessed foods dominate global diets, these findings add powerful evidence to a growing body of research. They suggest it’s time for nutrition advice to move beyond nutrients—and start addressing how foods are made, not just what they contain.

Takeaway

Following official dietary guidelines is a solid foundation for healthy eating—but this study suggests that what even when calories and nutrients are matched, minimally processed foods lead to greater benefits for weight, body fat, and appetite control.

So if you’re aiming to improve your health, don’t just focus on macros or labels—choose real, whole foods whenever you can. The evidence is clear: how we process food can shape how it affects our bodies.

Reference: UPDATE Trial (Ultra Processed versus Minimally Processed Diets following UK dietary guidance on health outcomes). ClinicalTrials.gov: NCT05627570. Published in Nature Medicine, Samuel J. Dicken et al, August 2025.