Do Ultra-Processed Foods Really Sabotage Weight Loss? Not Exactly

BONUS post: A breakdown of a recent study investigating ultra-processed foods and their role in weight loss.

On August 4th, 2025, a new study published in Nature Medicine made headlines with its findings on ultra-processed foods (UPFs) and their potential role as a barrier to weight loss. In today’s post, I’ll walk you through the key takeaways from the research and share my perspective on what these results might mean for everyday food choices.

Summary of study design and methods:

This was a randomized crossover trial involving 55 adults. Researchers compared weight loss on two diets: one made up of ultra-processed foods (UPFs) and the other of minimally processed foods (MPFs). At baseline, participants’ diets were at least 50% ultra-processed (measured by a 24-hour recall).

Each participant followed one diet for 8 weeks, had a washout period, then switched to the other diet. A unique feature of this trial is that both diets were designed to follow current public health dietary guidelines, specifically, the UK’s Eatwell Guide.

These guidelines include choosing foods lower in saturated fat, added sugar and salt, consuming five daily portions of fruit and vegetables, basing meals on starchy carbohydrates and eating a variety of foods in the right proportions.

To keep things tightly controlled, all meals were provided by researchers. Participants were given more than enough food and told to eat as much as they wanted.

Foods were categorized using the NOVA classification system, which defines foods by the extent of processing:

• Unprocessed or minimally processed foods: fruits, vegetables, seeds, eggs

• Processed culinary ingredients: oils, butter, sugar, salt

• Processed foods: canned vegetables or fruit, cheese, fresh bakery bread

• Ultra-processed foods: sausages, burgers, granola bars, most breakfast cereals, breads with additives, processed protein products (like chicken nuggets), flavoured yogurt

In addition to weight change, the researchers also measured body composition, blood markers, and appetite across the two diets.