The clinical trial, consisting of 55 adults (mostly women) from the United Kingdom who were overweight or had obesity, followed participants on these diets for eight weeks each.
At the end of the trial, participants eating minimally processed foods like overnight oats and homemade pasta or chicken dishes lost roughly 2 percent of their baseline weight. They also self-reported more significant improvements in their ability to control cravings compared with people on the ultra-processed diet.
However, people on the ultra-processed diet also lost weight — around 1 percent of their baseline — eating items like frozen meals and breakfast bars.
“We didn’t expect to see weight loss on the ultra-processed food diet, but this is likely because participants had an unhealthy diet at baseline that did not follow dietary guidance, and improved on the ultra-processed diet,” says lead study author Samuel Dicken, PhD, a research fellow at University College London’s department of behavioral science and health and Centre for Obesity Research in England.
Is the Difference in Weight Loss Meaningful?
Dr. Dicken and the other authors say that although a 2 percent reduction in weight on the minimally processed diet may not seem like much, it’s notable for an eight week period involving study subjects not actively trying to eat less, and that over the course of a year it could translate to a weight reduction of 13 percent in men and 9 percent in women.
For people on the ultra-processed diet, though, weight loss over a year could be much less — 5 percent in men, 4 percent in women.
“The results first highlight the importance of existing dietary guidance,” Dicken says. “Then, choosing minimally processed foods over ultra-processed foods may help with losing weight more easily and maintaining a healthier weight long term — with benefits to body composition related to cardiometabolic health.”
How the Study Worked
After being split into two groups, one set of participants started off with eight weeks of eating minimally processed foods before returning to their normal diet for four weeks as a reset — then switching to the ultra-processed food diet for another eight weeks. The other group followed this eating pattern in the opposite order.
With much of the existing evidence on processed foods stemming from observational studies, this first-of-its-kind interventional study aimed to investigate causal links between diet and weight outcomes.
Can Ultra-Processed Foods Be a Part of Your Diet in Moderation?
The study findings add a slight twist to previous research.
“In this new study, because participants in both groups actually lost weight, this challenges the argument that ultra-processed foods always promote weight gain when nutrient balance is maintained,” says Stephen Finney, MD, a primary care and obesity medicine physician at Southcoast Health in North Dartmouth, Massachusetts.
“The main difference was that the minimally processed diet promoted lower cravings and food intake despite equal macronutrients,” he adds.
But for experts like Courtney Pelitera, RDN, a registered dietitian-nutritionist with Top Nutrition Coaching in New York, the finding that weight loss can still occur while eating ultra-processed foods is encouraging when it comes to reducing judgment around food choices.
“This should give confidence that eating processed foods occasionally as part of an overall healthy diet should not affect weight loss strategies,” says Pelitera. “A main priority is to eat on a consistent basis and fuel your body as much as it needs to function optimally, then focus on adjusting to mostly whole foods — but this does not have to be an all-or-nothing mentality. If one or two processed foods are in the diet each day, this study helps to prove that healthy weight loss can still be achieved.”
Study Has Some Limitations
The study authors state that the results may not be generalizable to all populations, as people with dietary restrictions, certain chronic diseases, and other factors were excluded from the trial. Researchers were also not able to directly measure participants’ food intake or confirm their adherence to the diets outside of what was self-reported.
Some other study limitations include the small sample size, short trial duration, and the food delivery model, which “does not reflect real-world access to food,” Dr. Finney notes, underscoring that food environments (what’s available and marketed to a particular community) help shape health.
“In the meantime, I recommend that individuals aim to cook simple meals when possible, enjoy packaged foods occasionally, and approach nutrition with both flexibility and awareness,” he says. “The goal is long-term balance, not guilt.”