Fit Teenage Boys Are Smarter

Yep.

"In the first study to demonstrate a clear positive association between adolescent fitness and adult cognitive performance, Nancy Pedersen of the University of Southern California and colleagues in Sweden find that better cardiovascular health among teenage boys correlates to higher scores on a range of intelligence tests - and more education and income later in life."

Actually, it has been known, and should be obvious, that fat kids (and adults) are stupider than fit ones. (e.g., see here and here)