A groundbreaking study conducted by South Dakota State University reveals that older adults who reduced their consumption of ultra-processed foods experienced significant health benefits. The research, which was meticulously controlled, demonstrated that participants naturally consumed fewer calories, lost weight and abdominal fat, and showed improvements in insulin sensitivity, nutrient-sensing hormones, and inflammation.
“Counting nutrients is not enough,” stated Moul Dey, professor of health and nutritional sciences. “The degree of processing changes how the body handles those same nutrients. Diet quality depends not only on nutrients but also on the ingredients and the level of processing, considered together.”
Context and Background
For decades, the Dietary Guidelines for Americans have advocated for balance and moderation. However, despite these recommendations, obesity and chronic diseases have continued to rise. Notably, the current guidelines do not explicitly address ultra-processed foods. This study is the first to demonstrate that when diets align with these guidelines while minimizing ultra-processed foods, calorie intake decreases and metabolic health improves significantly.
Ultra-processed foods, which dominate modern diets, are industrial products made by reconstructing parts of whole foods with synthetic additives such as flavors, colors, preservatives, and emulsifiers. These foods provide more than half of U.S. adults’ daily calories and about 70 percent of the national food supply. Simply put, if a food product is wrapped in plastic and lists ingredients unfamiliar to a home kitchen, it is likely ultra-processed.
Study Design and Findings
The meals in the study were crafted by the university’s human nutrition research team and prepared by a professional chef. Participants consumed these meals at home, reflecting realistic eating patterns. Unlike previous trials conducted entirely within research centers, this study tested a more practical approach by reducing ultra-processed foods from about half of daily calories to approximately 15 percent within nutritionally balanced menus for older adults.
“Older adults often face metabolic challenges as appetite and energy needs shift,” explained Dey, the senior author and principal investigator of the study. “We saw that when ultra-processed food intake went down, total calories and metabolic risk markers did too.”
Saba Vaezi, a doctoral student researcher and first author of the study, highlighted the simplicity of the approach. “Participants did not count calories or follow complicated weight-loss instructions,” she noted.
Robust Study Design
The study is among a select few rigorously controlled feeding trials in free-living older adults that:
- Tested two low–ultra-processed diets aligned with the Dietary Guidelines for Americans; one featuring a meat-based (lean pork) diet and the other a plant-based (lentil) diet.
- Matched the diets for calories, protein, fat, carbohydrate, fiber, and other key nutrients; a few familiar ultra-processed items were included in moderation to support adherence.
- Prepared and served more than twelve thousand pre-portioned meals from scratch to study participants.
Participants completed an 18-week feeding study with two diet periods of eight weeks each, separated by a short break. Each meal and snack was fully prepared and provided for home consumption. A companion method paper published in Current Developments in Nutrition confirmed strong participant adherence and described the complex operations that made this real-world feeding study possible.
Implications and Future Directions
On average, participants spontaneously reduced calorie intake, losing about 10% of total body fat and 13% of belly fat during both diet phases. They also experienced a 23% improvement in insulin sensitivity and favorable changes in inflammatory markers and nutrient-sensing hormone levels. Daily calorie intake decreased by roughly 400 calories per day, even without instructions to restrict calories. These results suggest that replacing ultra-processed foods with minimally processed ones can enhance metabolic efficiency and body composition in older adults within balanced, American Guidelines–aligned diets.
Researchers acknowledge the study’s small sample size of 36 participants and emphasize the need for larger studies to confirm long-term outcomes. At the one-year follow-up, as participants’ ultra-processed food intake increased, many metabolic improvements diminished, indicating that sustained reductions are essential for lasting benefits. The consistency of effects across both diet patterns underscores the central role of food processing in metabolic health.
“This study moves past the usual debate over whether plant-based or animal-based diets are better,” Dey concluded. “Both can be health-promoting when foods are simply prepared and nutritionally balanced.”
