A new controlled feeding study suggests that older adults may see metabolic benefits when ultraprocessed foods make up a smaller share of their diets, even when total nutrients stay the same.
Researchers at South Dakota State University tested what happened when adults aged 50 and older reduced ultraprocessed foods from about half of their daily calories to roughly 15 percent. Importantly, both study diets, one built around lean pork and one built around lentils, were nutritionally balanced and aligned with the current Dietary Guidelines for Americans.
Because all meals were prepared and portioned for participants, researchers could measure how food processing level affected everyday eating patterns without asking people to restrict calories or follow a weight-loss plan.
“Counting nutrients is not enough,” said senior author Moul Dey. “The degree of processing changes how the body handles those same nutrients.”
Ultraprocessed foods are industrially formulated products made from refined ingredients and additives. They’re common in modern diets and can be part of a balanced eating pattern, but researchers are still working to understand how processing level affects appetite, fullness and metabolic markers. The goal of this trial wasn’t to eliminate ultraprocessed foods entirely, but to test whether lowering them within otherwise balanced menus changed how much people ate and how their bodies responded.
During the study, which was published in Clinical Nutrition, participants naturally ate about 400 fewer calories per day and saw improvements in abdominal fat, insulin sensitivity and inflammation. These shifts appeared across both diet patterns, suggesting the level of processing, rather than protein source, played a larger role.
“Participants did not count calories or follow complicated weight-loss instructions,” said first author Saba Vaezi.
The researchers noted that the trial was small, with 36 adults completing the full 18-week study. A one-year follow-up suggested that many metabolic gains lessened when participants returned to higher levels of ultraprocessed foods, indicating that benefits may depend on maintaining the shift.
Still, the consistent results across both diets point to an emerging idea: Within nutritionally balanced eating patterns, replacing some ultraprocessed foods with more simply prepared options may help older adults eat less without trying and support healthier metabolism.
“This study moves past the usual debate over whether plant-based or animal-based diets are better,” Dey said. “Both can be health-promoting when foods are simply prepared and nutritionally balanced.”
This study was funded by the National Pork Checkoff and the USDA’s National Institute of Food and Agriculture.