Timed exercise reduces insulin resistance but not liver fat
The findings were published online in Diabetologia.
The study population included men and women living in the greater Leiden area in the western Netherlands who were aged 45-65 years and self-reported a BMI of 27 or higher. A second cohort included inhabitants of one municipality who were invited to participate regardless of their BMI. All wore the activity monitors for 4 consecutive days and nights during their usual activities.
Neither sedentary time nor breaks in sedentary time (defined as a period of activity with an acceleration greater than 0.75 m/s2 following a sedentary period) were associated with lower insulin resistance, as calculated by blood sampling.
However, the number of breaks in sedentary time was associated with a significant 22% higher liver fat content, assessed with proton magnetic resonance spectroscopy.
One reason for the lack of effect of breaks on insulin resistance, the authors theorized, is that this was a real-world observational study where regular breaks aren’t common. Alternatively, people might not have been intensively active enough during breaks to make a difference.
After adjustment for total body fat, an additional hour of MVPA was associated with a 5% drop in insulin resistance. An additional hour of MVPA in 5-minute bouts was associated with 9% lower insulin resistance.
Also after adjustments, insulin resistance was reduced significantly in participants who were most active in the afternoon, by 18%, or evening, by 25%, whereas insulin resistance was not affected among those who were most active in the morning (–3%), all compared with people who distributed their MVPA throughout the day.
Timing of MVPA was not associated with liver fat content, and there were no significant differences in liver fat content and insulin resistance between groups based on timing of light physical activity.
“This is just speculation, but perhaps for fat accumulation in the liver the circadian system is less involved. Or perhaps timing of other lifestyle variables are more important here, such as dietary intake,” Mr. van der Velde said.
Finally, he observed, “timing of physical activity is most likely just a piece of the puzzle. Timing of other lifestyle behavior, such as sleep, and food intake are important cues for our circadian system as well, and it is likely that all these behaviors interact with each other.”
The NEO study is supported by Leiden University Medical Center, the Netherlands Cardiovascular Research Initiative, an initiative supported by the Dutch Heart Foundation, and the Netherlands Organisation for Health Research and Development/Partnership Diabetes/Dutch Diabetes foundation Breakthrough. Mr. van der Velde has reported no further disclosures.
A version of this article first appeared on Medscape.com.