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It was a simple switch: trade your breakfast bar for a bowl of overnight oats. Your microwave meal for something cooked from scratch. But for the 50 people who did just that in a new UK trial, the results were profound.
A new randomized controlled study published in Nature Medicine has shown that people lose significantly more weight, more body fat, and report fewer cravings when they follow a diet made of minimally processed food compared to one made of ultra-processed foods—even when both diets meet official health guidelines.
Other than the diet change, the trial didn’t interfere with the participants’ daily routine. Participants stayed in their homes, ate meals delivered to their doors, and were told to eat as much or as little as they wanted. This approach made it the first major “real-world” test of what happens when we trade ultra-processed foods (UPFs) for meals cooked from scratch.
Both groups slightly lost weight, although those on the minimally processed diet lost more weight (2% compared to 1% in the UPFs group).
“Though a 2% reduction may not seem very big, that is only over eight weeks,” said Dr. Samuel Dicken, first author of the study from University College London, as per The Telegraph. “If we scaled these results up over the course of a year, we’d expect to see a 13% weight reduction in men and a 9% reduction in women on the minimally processed diet.”
The Hidden Cost of Ultra-Processing
The study, named the UPDATE trial, enrolled 55 adults who were either overweight or living with obesity. Over a two-month period, each participant followed two different diets, one after the other, with a four-week break in between. The diets were carefully matched to follow the UK’s Eatwell Guide—ensuring they had similar levels of fat, sugar, salt, fiber, and calories.
The only major difference? One was built around homemade, minimally processed meals—think chicken salad, overnight oats, and spaghetti bolognese. The other featured ultra-processed options like protein bars, packaged wraps, and low-fat ready-made lasagna—products often plastered with “healthy” labels in the supermarket.
Both sets of meals were delivered daily. Participants received around 4,000 calories per day and were told to eat freely, mimicking real-life eating behavior.
By the end of each diet phase, both groups lost weight. But those on the minimally processed diet lost nearly double: an average 2.06% of their body weight, compared to 1.05% for those eating ultra-processed food.
Even more striking: the weight loss on the homemade diet came from fat. Participants shed more body fat percentage, visceral fat, and even reported better control over cravings, especially for savory foods.
Calories Weren’t the Whole Story
For decades, nutrition science focused on fat, sugar, and salt. But this trial reminds us that “calories in, calories out” misses the whole picture — because how food is made may matter as much as what it contains.
The ultra-processed foods in the study weren’t junk food. In fact, they were nutritionally balanced, aligned with official guidance, and chosen specifically to avoid high levels of saturated fat or sugar. But participants still lost less fat and reported higher levels of fatigue, gastrointestinal problems, and craving difficulty on the UPF diet.
“Previous research has linked ultra-processed foods with poor health outcomes,” said Dr. Dicken. “But not all ultra-processed foods are inherently unhealthy based on their nutritional profile.”
So what’s going on?
Researchers point to several possibilities. Ultra-processed meals tend to be more energy-dense, softer in texture, and easier to eat quickly—all traits that encourage overconsumption. In this study, participants on the UPF diet consumed about 120 fewer calories than usual. Those on the minimally processed diet, however, cut nearly 290 calories without even trying.
“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 senior authors of the study and the author of Ultra-Processed People.
And though both diets led to modest improvements in cholesterol, blood pressure, and glucose, only the minimally processed diet significantly lowered triglycerides. Surprisingly, the UPF diet slightly improved LDL (“bad”) cholesterol—but without significant fat loss.
Real Meals, Real Lives, Real Consequences
The strength of this study lies in its realism. Participants lived at home. They weren’t trying to lose weight. They weren’t told to restrict calories. Their meals came in supermarket packaging—complete with health claims and nutrition labels.
And yet, people responded differently depending on how the food was made.
“These findings support what we have long suspected—that the way food is made might affect our health, not just the nutrients it contains,” said Tracy Parker, a senior dietitian at the British Heart Foundation, as per The Telegraph.
Importantly, this was not a study of people eating burgers and soda versus salads and lentils. Both diets adhered to national guidance. That makes the outcome even more sobering.
Despite being healthier than their usual diets, the UPF meals provided by the study still led to less fat loss, more adverse effects, and less control over cravings.
Researchers estimate that if maintained over a year, the homemade diet could lead to 13% weight loss for men and 9% for women. The UPF diet? Only about 4–5%.
Still, the researchers are careful not to demonize all UPFs. “Completely cutting UPFs out of our diets isn’t realistic for most of us,” said Parker. “But including more minimally processed foods—like fresh or home-cooked meals—alongside a balanced diet could offer added benefits too.”
When Personal Health Meets Corporate Power
Today, ultra-processed food makes up more than half of all calories consumed in the UK. And that’s no accident. These foods are cheap, convenient, aggressively marketed, and engineered to be irresistible.
The researchers behind the UPDATE trial say that fixing this isn’t just about telling people to cook more.
“The global food system at the moment drives diet-related poor health and obesity,” said Prof. van Tulleken. “Particularly because of the wide availability of cheap, unhealthy food.”
Their message to policymakers is clear: nutrition labels and ingredient lists aren’t enough. It’s time to consider the role of processing itself—and to rethink how we structure our food environments.
As obesity continues to rise in the UK and across the globe, this trial offers something rare in nutrition science: clarity.
Cooking more meals from scratch might be one of the most powerful tools we have for losing weight, controlling cravings, and—perhaps most importantly—rethinking how we feed ourselves.
Dining and Cooking