Can a diet based on ultra-processed foods be healthy? • Stronger by Science

You’ve likely heard that ultraprocessed foods are among the worst things you can consume for your health and body composition, with observational studies linking high intake of ultra-processed foods with everything from weight gain and metabolic issues to higher mortality risk. At the same time, you’ve also likely heard that there aren’t inherently any “good” or “bad” foods and that as long as you manage your energy intake, hit your fiber intake and do your best to consume mostly whole foods, the inclusion of some ultra-processed foods is likely not a big deal from a health perspective.

But what if you were to consume only ultra-processed foods while still adhering to general nutrition guidelines, and how would that compare to a minimally processed diet following the same guidelines?

A new randomized crossover study examined exactly that. The study included 55 adults who were overweight or obese and had them follow either an ultra-processed or a minimally processed diet. The really cool thing about the design of this study was that participants underwent quite a few assessments to give us a more nuanced understanding of how both diets affected them, including body composition (via bioelectrical impedance analysis, or BIA), fasting biomarkers, heart rate, blood pressure, and more. 

They were first randomized to either the ultra-processed or minimally processed diet, and then followed their assigned diet for 8 weeks. They were then retested midway and at the end of the 8-week period. After another 4-week washout period, they had a 2-week baseline period before being assigned to the opposite diet for another 8 weeks and being retested at the end. Quite the study design if you ask me. 

Both diets were specifically designed to meet the United Kingdom’s national dietary guidelines, as outlined by the Eatwell Guide, and participants were provided with all their meals and were instructed to not consume any other food or drink except water. However, the researchers were kind enough to provide coffee and tea. The researchers made a deliberate effort to match the two diets in terms of calories, macronutrient distribution, fiber, sodium, saturated fat, and intake of fruits and vegetables. The minimally processed diet consisted of foods such as whole fruits, vegetables, legumes, plain meats, eggs, and whole grains, all prepared with minimal industrial intervention. The ultra-processed diet included foods like sweetened yogurts, packaged cereals, reconstituted meats, ready meals, snack bars, and diet soft drinks. 

However, the slight catch here is that the study was conducted under free-living, ad libitum conditions, meaning people ate at home and were allowed to consume as much or as little as they wanted, but only from the foods provided. Although this is a cool design from an ecological validity perspective, it’s worth mentioning that it increases the risk of non-compliance, especially when examining bodyweight or body composition outcomes, given that participants were asked to self-report their energy intake.

Onto the results!

*cue dramatic music*

The minimally processed food diet led to greater weight loss (-2% vs -1% of body weight) and only the minimally processed diet significantly reduced fat mass, body fat percentage, and visceral fat rating, but the decreases weren’t anything insane (eg: body fat percentage decreased by -0.76%). Participants also reported better control over cravings, and their daily energy intake ultimately decreased by about 330 calories compared to the ultra-processed diet. This is an important point, though, as a ~300 calorie difference is pretty meaningful when it comes to the magnitude of a calorie deficit. That said, it also hints that although the ultra-processed foods were “nutritionally adequate” on paper, their texture, taste, or ease of eating could have led people to eat more. 

Additionally, both diets improved certain metabolic markers, such as triglycerides, glucose, and cholesterol; however, these changes were relatively modest and similar between groups. 

So what can we take away from this?

It appears that consuming an ultra-processed diet is not necessarily the worst thing for your body composition or health, provided it adheres to general health guidelines. This is a pretty important catch, though, as the participants still ticked a lot of nutrition boxes and followed general health guidelines despite following an ultra-processed diet. They were also provided all their meals, something that may not necessarily fully reflect how many people “interact” with ultra-processed foods. That said, although this is a somewhat positive finding for those who may not be able to always consume minimally processed foods, it does highlight that even a “healthy” ultra-processed diet can potentially lead to overeating and thus have negative effects on body composition and health in the long term. 

As a general guideline, doing your best to consume mostly whole foods is still the best way to approach your diet, but don’t overstress if you have to consume some ultra-processed foods here and there, especially if you still adhere to general nutrition guidelines.