A new study from South Dakota State University shows that older adults who ate fewer ultra-processed foods naturally ate fewer calories, lost body fat—especially around the belly—and improved their overall health.
These changes happened without counting calories or following strict diets.
The research was led by Professor Moul Dey and her team. It looked at how food processing, not just nutrients, affects the body. For years, dietary guidelines have encouraged people to eat balanced meals and avoid too much fat or sugar, but rates of obesity and chronic illness have continued to rise.
This study shows that reducing ultra-processed foods—even when the diet meets all standard nutrition guidelines—can lead to better health results.
Ultra-processed foods are industrial products made by breaking down whole foods and adding artificial flavors, colors, preservatives, and other chemicals.
They make up more than half of the daily calories most adults in the U.S. eat and about 70% of the food supply. If it comes wrapped in plastic and contains ingredients you wouldn’t keep at home, it’s probably ultra-processed.
The study gave older adults home-delivered meals prepared by a professional chef. These meals followed the Dietary Guidelines for Americans and were low in ultra-processed foods.
Each person ate two different meal plans over 18 weeks—one based on lean pork as the main protein, and another based on lentils, beans, and peas. Both diets were matched for nutrients, including protein, fat, fiber, and carbs.
Unlike past studies done entirely inside labs, this one let participants eat at home, following real-world eating habits. In total, the team prepared over 12,000 pre-portioned meals for 36 older adults. The diets were given in two eight-week periods, separated by a short break.
The results were impressive. On average, participants ate about 400 fewer calories each day without trying to diet. They lost about 10% of their total body fat and 13% of their belly fat. Their insulin sensitivity improved by 23%, and other signs of inflammation and hormonal balance also got better.
Importantly, these benefits happened whether the diet was meat-based or plant-based. This suggests that it’s not about whether you eat meat or plants, but how processed the food is. Both diet types helped as long as the meals were made with minimally processed ingredients.
The study had a small group of participants, and the researchers say more studies are needed to confirm the long-term effects. Still, this study stands out because it showed that just eating less ultra-processed food—without any special dieting rules—can lead to real health improvements in older adults.
One year after the study ended, participants’ eating habits returned to include more ultra-processed foods, and many of their health gains faded. This shows that to keep the benefits, people need to keep ultra-processed foods low in their diets over time.
The takeaway is clear: switching to less processed foods can help improve health, especially for older adults. This study also shows that both meat-based and plant-based diets can be healthy when they are simply prepared, balanced, and low in processed ingredients.
If you care about weight loss, please read studies that hop extract could reduce belly fat in overweight people, and early time-restricted eating could help lose weight .
For more health information, please see recent studies that Mediterranean diet can reduce belly fat much better, and Keto diet could help control body weight and blood sugar in diabetes.
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