* * *
It turned out that these genetically identical twins looked surprisingly different beneath the skin and skull. The sedentary twins had lower endurance capacities, higher body fat percentages, and signs of insulin resistance, signaling the onset of metabolic problems. (Interestingly, the twins tended to have very similar diets, whatever their workout routines, so food choices were unlikely to have contributed to health differences.)
-from "One Twin Exercises, the Other Doesn't" in the March 4, 2014 digital edition of the NYT.
The study is published in the March 2015 Medical & Science in Sports & Exercise Journal. The abstract is here.
I like the reference to more "grey matter." I need all of that I can get. And I'm hoping this also applies to people who exercise but don't have a sedentary twin.