Study: Replacing 30 Minutes of Sitting with Physical Activity or Sleeping May Affect Body Weight

A CPS-3 Study

Researcher: Erika Rees-Punia, PhD, MPH 
Institution: American Cancer Society 
Area of Focus: Epidemiology and Behavior Research, Population Science

The Challenge: For every minute in a 24-hour day, we’re basically doing 1 of 3 things—sleeping, sitting (being sedentary), or being physically active. Since you can do only one of these at a time, these behaviors are mutually exclusive. Yet, they’re uniquely interrelated because the more time you spend doing one, automatically means you’re spending less time doing the others.

What you’re doing every minute in a 24-hour-day may also relate to your body weight. To truly understand some of the intricacies of weight change and maintenance requires consideration of these 3 behaviors simultaneously. 

The Research: Erika Rees-Punia, PhD, MPH, and her ACS research colleagues were able to analyze these 3 behaviors together in a racially diverse subset of 549 participants in the Cancer Prevention Study-3 (CPS-3) who agreed to be part of in an accelerometer sub-study

These study participants answered survey questions every 3 years like all CPS-3 participants, and in addition wore an activity monitor, or accelerometer, around their waists for 7 consecutive days except when sleeping. This amount of monitoring allows for a very accurate snapshot of how people typically spend a day compared with answering survey questions, which rely on memory.

Rees-Punia and her team used compositional data analysis methods to analyze longitudinal data that makes up parts of a finite whole—like a 24-hour day. Specifically, they looked at survey data across 3 years to see how different types of activity filled up all the time in a whole day. 

The researchers analyzed accelerometer-measured time people were physically active and sitting as well as self-reported sleep time, and they explored the association of these behaviors together with 3-year weight change.  

They found that the amount of time people spend sleeping, being physically active, and being sedentary is associated with a change in weight among women (but not men) and among Latinx and White participants (but not Black participants). 

They also found that: 

  • Replacement of 30 minutes/day of sedentary time with 30 minutes of moderate-vigorous intensity physical activities (like brisk walking, jogging, or playing tennis or basketball, etc.) was associated with ~3.5 lbs. weight loss among Latinx participants.
  • Replacement of 30 minutes/day of sedentary time with 30 minutes of sleep was associated with ~1.5 lbs. gain in White women and ~1.3 lbs. gain in White men.

Why Does It Matter? Researchers have used these techniques for many years in nutritional and some other studies, but they’ve only recently been using them in physical activity epidemiology studies. 

This study of weight change, along with other types of analysis, is the first of its kind, and allowed Rees-Punia and her colleagues to model what would theoretically happen to participants’ weight if they were to replace 30 minutes a day of sedentary time with other behaviors.