Children don’t need big changes in their daily habits to improve their health. For example, replacing just 30 minutes of sitting with vigorous exercise daily can help lower body fat, and replacing this amount of sitting time with sleep can improve blood sugar regulation, according to a new study from researchers at the Keck School of Medicine of the University of Southern California.  

The research, supported by the Southern California Clinical and Translational Science Institute (SC CTSI), was published in The Journal of Pediatrics. According to the CDC, vigorous exercise is defined as physical activity that increases your heart rate and breathing, such as running, jogging, jumping rope, swimming, or related activities.

“We wanted to understand how lifestyle behaviors might alter a trajectory toward obesity and type 2 diabetes,” said Jasmin Alves, PhD, first author of the paper and a postdoctoral fellow in the lab of senior author Kathleen Page, MD, Professor of Medicine and Pediatrics and Co-Chief of Endocrinology and Diabetes at USC Keck. Page is a former KL2 Scholar and is currently the Co-Director of the Research Development core at the SC CTSI.
 

The researchers followed 54 children, aged 7 to 11, who participated in the broader USC BrainChild project. Each participant completed two clinical visits approximately two years apart. At both visits, fasting blood samples were collected to measure metabolic markers, including insulin levels and insulin resistance.

Between visits, the children wore wrist accelerometers continuously for one week. The devices provided objective data on how much time participants spent sleeping, sitting, or engaging in light, moderate, and vigorous physical activity.

The study used a relatively new “time swap” statistical method known as isotemporal substitution modeling. The researchers tracked the cohort’s sleep, screen and activity using wrist devices. Then the study used the time swap method to examine metabolic markers when small chunks of time—15 to 30 minutes—were changed from sedentary activity to light, moderate or vigorous play, or to sleep. 

“This method allows us to examine behaviors as components of a fixed 24-hour day,” Alves said. “If time is reduced in one area, such as sedentary behavior, that time must be reassigned elsewhere.” 

This is the first longitudinal study in children to show how specific time swaps can change body fat and insulin regulation over time. 

If children spent 30 minutes sleeping instead of sedentary activity, that change was associated with lower insulin secretion over time. Lower insulin secretion may reflect improved insulin sensitivity, which could help lower the risk of diabetes. 

“When sleep or sedentary time is analyzed independently, associations may not be apparent,” Alves added. “Examining them simultaneously revealed meaningful changes, since more time in one behavior must come from time in another.”

Vigorous physical activity—running, playing soccer, jumping, high‑energy play—had a stronger impact on reducing body fat over two years than moderate activity, such as walking.

“Small changes can lead to big results, and swapping sedentary time for sleep or vigorous activity can protect the child's metabolic health as they grow,” Page said.

Alves emphasized that the study’s implications extend beyond simply encouraging more exercise, and the researchers hope to follow these children into adulthood. The support from SC CTSI enabled longitudinal follow-up from the USC Brainchild project. Understanding trade-offs may help researchers design more realistic interventions. Because the study was observational, it cannot establish cause and effect. Participants did not modify their routines; instead, the modeling estimated potential outcomes associated with hypothetical behavioral shifts.

The public health message is that shifts in children’s daily routines, trading a little screen time for vigorous play and a bit more sleep, can reduce body fat and improve insulin regulation, potentially lowering their future risk of obesity and type 2 diabetes. Instead of calling for drastic overhauls, the findings support simple, concrete time swaps within a child’s existing 24‑hour day.

“This study serves as foundational work and a statistical roadmap for potential clinical trials,” Alves said.