You have likely heard countless times that ultra-processed foods are among the worst things you can consume for your overall health and body composition. Observational studies frequently link a high intake of ultra-processed foods with a wide array of negative health outcomes, ranging from unwanted weight gain and metabolic complications to a higher overall mortality risk. At the same time, you have probably also heard the common dietary counter-argument that there are not inherently any "good" or "bad" foods. According to this perspective, as long as you manage your total energy intake, hit your daily fiber targets, and do your best to consume mostly whole foods, the occasional or even moderate inclusion of ultra-processed foods is likely not a big deal from a long-term health perspective.
Yet a lingering question remains in the nutritional sciences: What if you were to consume a diet composed entirely of ultra-processed foods while still strictly adhering to general national nutrition guidelines, and how would that compare directly to a minimally processed diet following the exact same guidelines?
A new randomized crossover study examined precisely that question, offering a fascinating look into the nuances of food processing and human metabolism. The study included 55 adult participants who were classified as either overweight or obese. Researchers assigned these participants to follow either an entirely ultra-processed diet or an entirely minimally processed diet over a prolonged period. One of the most robust aspects of the study design was the extensive battery of assessments and measurements utilized to give researchers a deeply nuanced understanding of how both dietary approaches affected the participants. These assessments tracked changes in body composition using bioelectrical impedance analysis, commonly known as BIA, as well as fasting biomarkers, heart rate, blood pressure, and several other vital health metrics.
The trial followed a rigorous crossover methodology. Participants were first randomized to either the ultra-processed diet or the minimally processed diet and maintained their assigned regimen for a duration of eight weeks. Researchers retested the participants midway through and at the final conclusion of this initial eight-week period. Following this first phase, the participants underwent a four-week washout period, giving their bodies time to adjust back to baseline. This was followed by a subsequent two-week baseline period before they were assigned to the opposite diet for another eight weeks. At the end of the second dietary intervention, they were retested once again. It is a remarkably thorough study design that helps minimize confounding variables by having participants act as their own controls.
Both diets were specifically engineered to meet the United Kingdom’s national dietary guidelines, closely mirroring the standards outlined by the official Eatwell Guide. To ensure compliance and control, participants were provided with all of their meals directly from the research team. They were explicitly instructed not to consume any other food or drink outside of the provided provisions, with the exception of water. However, the researchers did accommodate everyday habits by providing coffee and tea to the participants.
A central pillar of the study design was the deliberate effort by researchers to match the two distinct diets across numerous nutritional parameters. The menus were carefully calibrated to be comparable in terms of total calories, macronutrient distribution, fiber content, sodium levels, saturated fat, and the inclusion of fruits and vegetables. Despite these tight controls on paper, the physical nature of the foods differed starkly. The minimally processed diet consisted of traditional, whole foods such as fresh fruits, vegetables, legumes, plain cuts of meat, eggs, and whole grains, all prepared with minimal industrial intervention. Conversely, the ultra-processed diet featured commercially manufactured items such as sweetened yogurts, packaged breakfast cereals, reconstituted meats, ready-made convenience meals, snack bars, and diet soft drinks.
Despite the rigorous control over the nutritional content of the meals, there was a slight catch in how the study was executed: it was conducted under free-living, ad libitum conditions. This means that participants ate their provided meals at home and were allowed to consume as much or as little of the food as they wanted, provided they only ate what was supplied to them. While this kind of design is exceptionally valuable from an ecological validity perspective because it mirrors real-world human behavior more closely than a sterile laboratory setting, it does introduce certain limitations. Specifically, it increases the risk of non-compliance, particularly when examining outcomes related to body weight or body composition, given that researchers ultimately relied on participants to self-report their actual energy intake.
When the results were finally tallied, they provided a clear picture of how the two diets differed in practice. The minimally processed food diet led to greater weight loss, resulting in a reduction of two percent of body weight compared to just one percent of body weight on the ultra-processed diet. Furthermore, only the minimally processed diet produced statistically significant reductions in fat mass, overall body fat percentage, and visceral fat ratings. However, it is worth noting that these decreases were modest rather than dramatic, with body fat percentage, for instance, dropping by an average of just 0.76 percent.
Beyond body composition changes, participants reported experiencing better control over their food cravings while on the minimally processed diet. More importantly, their daily spontaneous energy intake ultimately decreased by about 330 calories compared to when they were consuming the ultra-processed diet. This distinction is vital because a calorie difference of approximately 300 calories per day is quite meaningful when attempting to create or maintain a calorie deficit for weight management. At the same time, this finding hints at a deeper underlying mechanism: although the ultra-processed foods were designed to be nutritionally adequate on paper, their physical texture, palatability, rapid rate of consumption, or overall ease of eating may have subtly encouraged participants to overeat.
In addition to the differences in weight and fat loss, both diets successfully improved certain metabolic markers among the participants, including improvements in triglycerides, fasting glucose, and cholesterol levels. However, these metabolic changes were relatively modest and remained largely similar between the two groups, suggesting that the basic nutritional adequacy of the diets played a protective role regardless of the level of food processing.
These findings offer several key takeaways for everyday nutrition and public health. Most notably, the data suggests that consuming an ultra-processed diet is not necessarily disastrous for your body composition or metabolic health, provided that the diet still adheres closely to general health and nutritional guidelines. This is a critical caveat, however, because the study participants were still ticking a lot of nutritional boxes—such as hitting fiber, fruit, vegetable, and macronutrient targets—despite the ultra-processed nature of their food items.
Furthermore, because participants were provided with all their meals pre-selected to meet national guidelines, the setup may not fully reflect how the average person interacts with ultra-processed foods in the chaotic reality of modern life, where such foods are often high in calories and low in fiber. That said, while these results offer a somewhat encouraging finding for individuals who may not always have the time or access to consume exclusively minimally processed foods, the research underscores a persistent risk. Even a nutritionally adequate, guideline-compliant ultra-processed diet still carries the potential to trigger overeating, which can ultimately lead to negative long-term effects on body composition and health over time.
As a general guideline for the public, making a consistent effort to consume mostly whole, minimally processed foods remains the best overall approach to building a healthy diet. At the same time, the research suggests there is no need to overstress or develop food anxiety if you occasionally have to consume ultra-processed products here and there, provided you maintain a balanced overall intake and continue to adhere to foundational nutrition guidelines.
