Research has suggested that sleep patterns can affect childhood weight gain.
Published in the journal Pediatrics, the study looked at 308 children aged between four and ten.
The team, from the University of Chicago Medical Center, took their BMIs and monitored their sleep patterns for a week.
They discovered that all the children slept for an average of eight hours a night.
However, those who had a BMI in the obese range slept for fewer hours and showed greater variability between weekend sleep time and school days sleep time.
The researchers concluded: "Obese children were less likely to experience 'catch-up' sleep on weekends, and the combination of shorter sleep duration and more-variable sleep patterns was associated with adverse metabolic outcomes."
The group in the overweight BMI category also showed an inconsistent sleep pattern.
Furthermore, an analysis of sleep patterns and blood markers showed that higher variance in sleep duration or shorter sleep duration was more likely to be linked to altered levels of insulin, LDL cholesterol and high-sensitivity C-reactive protein.