Weight loss doubles with minimally processed foods, new study finds

Swapping ultra-processed meals for home-cooked, whole food options can significantly boost weight loss, according to a major new clinical trial

A new study has found that people who eat minimally processed foods, such as home-cooked meals made with whole ingredients, lose twice as much weight as those consuming diets high in ultra-processed foods (UPFs), even when given nutritionally matched diets.

 

The findings come from a randomised controlled trial involving adults with overweight or obesity, conducted by researchers at the University College London (UCL) and the University College London Hospitals (UCLH).

 

The study, published in Nature Medicine, is the first to compare ultra-processed and minimally processed diets in real-world settings and is also the longest experiment of its kind so far.

 

 

What the study found

 

The trial involved 55 adults split into two groups. One group followed an eight-week minimally processed food (MPF) diet, with meals like overnight oats or homemade spaghetti. Then the group took a four-week break before switching to an UPF diet, including items like oat bars or ready-made lasagne. The other group followed the diets in reverse order.

 

Both diets were nutritionally balanced and based on the UK's Eatwell Guide, with similar levels of fat, protein, carbs, salt, and fibre. Participants received more food than they needed and were free to eat as much or as little as they liked.

 

Dr Samuel Dicken, first author of the study from the UCL Centre for Obesity Research and UCL Department of Behavioural Science & Health, said, "Previous research has linked ultra-processed foods with poor health outcomes. But not all ultra-processed foods are inherently unhealthy based on their nutritional profile. The main aim of this trial was to fill crucial gaps in our knowledge about the role of food processing in the context of existing dietary guidance, and how it affects health outcomes such as weight, blood pressure and body composition, as well as experiential factors like food cravings."

 

After each eight-week diet, both groups lost weight, likely due to eating better than usual. However, weight loss was greater on the MPF diet, with an average reduction of 2.06 per cent, compared to 1.05 per cent on the UPF diet.  The extra weight loss seen on the MPF diet came mainly from losing fat and body water, without affecting muscle or fat-free mass, suggesting a healthier overall body composition.

 

Commenting on the effects of the MPF diet, Dr Dicken said, "Though a 2 per cent reduction may not seem very big, that is only over eight weeks and without people trying to actively reduce their intake. If we scale these results up over the course of a year, we'd expect to see a 13 per cent weight reduction in men and a 9 per cent reduction in women on the minimally processed diet, but only a 4 per cent weight reduction in men and 5 per cent in women after the ultra-processed diet. Over time this would start to become a big difference."

 

What are UPFs and MPFs?

 

Ultra-processed foods are industrially processed and contain additives. UPFs include many of the things you find in the freezer aisle or store shelves such as:

 

• Packaged snacks and ready meals
• Sugary cereals, breakfast bars
• Fast food
• Ready-to-eat meals
• Items with long ingredient lists and additives

 

In contrast, minimally processed foods include:

 

• Fresh fruits and vegetables
• Whole grains
• Lean meats and legumes
• Homemade meals with limited added salt or sugar

 

"The global food system at the moment drives diet-related poor health and obesity, particularly because of the wide availability of cheap, unhealthy food. This study highlights the importance of ultra-processing in driving health outcomes in addition to the role of nutrients like fat, salt and sugar. It underlines the need to shift the policy focus away from individual responsibility and on to the environmental drivers of obesity, such as the influence of multinational food companies in shaping unhealthy food environments," said Professor Chris van Tulleken from UCL.

 

What does this mean for you?

 

Researchers suggest that UPFs may lead to:

 

• Overeating due to low satiety
• Disrupted hunger hormones
• Faster eating pace, which contributes to excess intake before the body registers fullness

Meanwhile, the minimally processed diet helped participants feel fuller longer, eat more slowly, and naturally reduce calorie consumption without intentional restriction.

 

The takeaway from the study is simple: it’s not just about eating less or moving more. It’s about getting back to basics with meals made with whole ingredients. 

Professor Rachel Batterham, senior author of the study explained that choosing less processed rather than ultra-processed ones is likely to offer additional benefits in terms of body weight, body composition and overall health. “The best advice to people would be to stick as closely to nutritional guidelines as they can by moderating overall energy intake, limiting intake of salt, sugar and saturated fat, and prioritising high-fibre foods such as fruits, vegetables, pulses and nuts,” she said.

 

Professor van Tulleken further explained that the real problem lies in a food system dominated by cheap, highly processed products with lower costs. He said, “Stakeholders across disciplines and organizations must work together and focus on wider policy actions that improve our food environment,” highlighting the need for warning labels, marketing restrictions, and subsidies to make healthy food more accessible.   

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This report is for informational purposes only and is not a substitute for professional medical advice.