A four-year study from the University of Southern California finds that greater intake of ultra-processed foods is linked to higher odds of prediabetes and early insulin resistance in young adults aged 17 to 22.
Ultra-processed foods make up a large share of the American diet, including fast food, packaged snacks, candy, soda and many restaurant items high in sodium, added sugars and unhealthy fats. Prior national analyses have found these foods account for more than half of U.S. daily calories.
Researchers at the Keck School of Medicine of USC examined how ultra-processed food intake relates to blood sugar control in young adults—a group less studied than older populations. The team followed 85 participants, ages 17 to 22 at baseline, drawn from the Metabolic and Asthma Incidence Research (Meta-AIR) study within the larger Southern California Children’s Health Study. All had a history of overweight or obesity in early adolescence.
Participants completed detailed 24-hour dietary recalls on a recent weekday and weekend day at an initial visit between 2014 and 2018, and again roughly four years later. Foods were classified as ultra-processed or not, and researchers calculated the share of each participant’s diet made up of ultra-processed foods by weight (grams). To assess glucose regulation, blood samples were collected before and after a standardized sugary drink as part of an oral glucose tolerance test.
The study found that each 10-percentage-point increase in ultra-processed food intake over time was associated with a 64% higher likelihood of prediabetes and a 56% higher likelihood of impaired glucose regulation. Participants with higher initial consumption also showed elevated insulin levels at follow-up—an early sign of insulin resistance.
“Even modest increases in ultra-processed food intake can disrupt glucose regulation in young adults,” said senior author Vaia Lida Chatzi, MD, PhD, a professor at USC’s Keck School of Medicine. “Young adulthood is a critical window for shaping long-term health,” she added. First author Yiping Li said limiting ultra-processed foods may help prevent prediabetes and type 2 diabetes in this population.
The findings, published in Nutrition & Metabolism, were supported in part by the National Institutes of Health and other funders. The authors call for larger, longer studies to pinpoint which ultra-processed foods pose the greatest risk and to clarify how specific nutrients and additives may affect insulin function and glucose control.
