Contrary to what many researchers expect, physically active older teens don't necessarily eat a healthier diet than their less-active contemporaries.And there appeared to be no link between body mass index (BMI) values and levels of physical activity, the research showed.The study of 900 Vancouver-area teenagers in Grades 10 through 12 was conducted by Dr. Catherine Sabiston, of McGill University, and P.R.E. Crocker, of the University of British Columbia (UBC).