The meta-analysis considered data from 10,455 subjects in 103 research reports.

"In studies that focused on exercise only, blood glucose improved twice as much as in studies that focused on exercise, diet and medication adherence," Vicki Conn, of the University of Missouri-Columbia Sinclair School of Nursing, said in a study.

It doesn't matter how overweight the patients are or how poor the current blood glucose was at the start of the studies, the improvements from exercise were equal across the board, according to the study published in Diabetologia.

"The censuses among these studies could mean that it is easier for people to focus on one thing at a time," Conn said. "It is easy for people to get overwhelmed when asked to make too many changes."