Can we say that inactivity and obesity are directly related? Scientists are still addressing this issue. The 2018 Physical Activity Council Participation Report shows that 82.4 million people—28% of the American population—are inactive. At the same time, the Centers for Disease Control and Prevention reports that more than one-third (36.5%) of U.S. adults are obese (NCHS Data Brief, No. 219, November 2015).

“The combination of inactive and underactive people is a setup for obesity, especially [when low activity levels are] combined with poor diet choices,” says William O. Roberts, MD, MS, FACSM, a professor in the department of family medicine and community health at the University of Minnesota. “Frank Booth, [PhD, based at the University of Missouri], has long suggested that humans have a gene that is turned on with inactivity to help the body store fat during lean times.”

In a comprehensive review study conducted under Booth’s leadership and published in the journal of Physiological Reviews (2017; doi:10.1152/physrev.00019.2016), researchers proposed that “physical inactivity could be considered a behavior selected by evolution for resting, and also selected by evolution to be reinforcing in life-threatening situations in which exercise would be dangerous.” Study authors also noted that human twin studies and rat selective-breeding studies have provided indirect evidence of genes with functions that produce physical inactivity. “However,” they added, “studies on the molecular neurobiology for physical inactivity are only in their infancy.” Keep watch for further developments in this line of research.

To learn more about the 2018 Physical Activity Council Participation Report, go to sfia.org/press/900_Physical-Activity-Study-Shows-28%25-of-Americans-Inactive. To read the Data Brief on obesity rates in the U.S., go to cdc.gov/nchs/data/databriefs/db219.pdf.