Well what a surprsie. It's not proof per se but it does indicate that the fitter you become the more likely you are to burn (rather than store) fat. And that process is cumulative - ie a good pattern of exercise behaviour fosters a positive feed-back loop of fat-burning potential.
Phys Ed: A Workout for Your Bloodstream - Well Blog - NYTimes.com
Phys Ed: A Workout for Your Bloodstream - Well Blog - NYTimes.com
What they found was that after 10 minutes of treadmill jogging or stationary-bicycle riding, the healthy adults showed enormous changes in the metabolites within their bloodstream, as did the less-fit group, although to a lesser degree. In particular, certain metabolites associated with fat burning were elevated. The fit adults showed increases of almost 100 percent in many of these molecules. The less-fit group had increases in those same metabolites of about 50 percent. As for the marathoners, their blood contained up to 10 times more of the fat-burning markers.
