In case you needed more incentive to cut down on ultra-processed foods, a new diet swap study out today reveals that people experienced greater weight loss while eating minimally processed foods than they did when they ate a nutritionally similar, ultra-processed diet.
In a six-month trial led by scientists at University College London, study participants were assigned one of the two diet regimes to follow for eight weeks, and then took a four week break before swapping to the other diet for another eight weeks. Participants lost more weight while eating the minimally processed diet than the ultra-processed one; they also shed more unhealthy fat. The findings, published Monday in Nature Medicine, suggest that, among other things, ultra-processed diets are especially good at stoking people’s food cravings, the researchers said.
Although there is some debate over what constitutes an ultra-processed food, there are generally considered products or ingredients that have gone through high levels of industrialized processing, like breakfast sausages, candy, or sodas. There is a growing mountain of evidence that suggests a diet rich in ultra-processed foods is less healthy overall than a diet made up of mostly whole foods, and that ultra-processed foods may raise the risk of certain diseases. Most of this research, however, only shows a correlation between ultra-processed diets and poorer health outcomes, and not a direct cause-and-effect link. Clinical trials can provide stronger evidence, but they’re notoriously difficult to do in the world of nutrition science for many reasons, particularly funding, the researchers said.
“Clinical trials are expensive, and there’s been a generally lower amount of funding for diet and nutrition research given its importance for health,” study author Sam Dicken, a research fellow at UCL’s department of behavioral science and health, told Gizmodo. “We were fortunate to have joint funding from a medical charity and a UK non-governmental organization to fund the trial.”
The study involved 55 adult volunteers who ate either a minimally processed diet or an ultra-processed diet made up of prepackaged meals for eight weeks, then took a four-week break before switching to the diet they hadn’t eaten yet for another eight weeks. Importantly, both eating regimens were crafted to follow the U.K.’s dietary recommendations, so the ultra-processed diet wasn’t designed to be vastly different in nutritional quality from the minimally processed diet. For example, the ultra-processed diet included breakfast cereal as a meal, while the equivalent minimally processed meal was overnight oats.
No matter which diet people followed, they lost weight, but the difference between the two regimens was significant. People eating a minimally processed diet lost an average of 2% of their baseline weight, while those on the ultra-processed diet lost an average of 1% and consumed slightly more calories overall. And people who lost weight on the minimally processed diet specifically lost more fat-related mass and visceral fat than they did on the ultra-processed diet. Visceral fat surrounds our abdominal organs and is associated with worse health outcomes than other types of fat found elsewhere in the body.
The results highlight the importance of following government dietary guidelines, Dicken said. But the study also indicates that people who want to lose weight may see the most benefit from sticking to minimally processed foods. As to why the ultra-processed foods are worse for dieting, the researchers have their educated guesses.
Ultra-processed foods tend to have more appealing textures and artificially boosted flavors, which often means they are softer or easier to eat, and tastier. Their appearance and packaging might also make them more visually appealing to potential customers. Interestingly, the volunteers in this study reported that both diets were equally satisfying to eat on average, but they also reported having better control over their cravings while on the minimally processed diet. Dicken noted that the researchers weren’t able to directly test these potential explanations in this trial, though, so more research is needed to know for sure.
The team has already launched their next study, which is testing out a behavioral support program to reduce people’s intake of ultra-processed foods. But Dicken cautioned that it will take widespread societal shifts, not individual scolding, to change our collective diets for the better.
“Policy actions that improve our obesogenic food environment and move away from individual responsibility are needed to ensure healthy diets are accessible and affordable for all,” he said.
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