SELMA, ALA. - On stage, the famous jazz pianist Thelonious Monk wore a collard-leaf pin in his lapel - an act of solidarity, in the guise of a key Southern food, with his sharecropper roots. Standing in front of Selma High School the other day, principal Roosevelt Wilson broke with Mr. Monk and proclaimed war on the humble but proud collard, the leafy green usually cooked with lard, and all the other unhealthy Southern foods it evokes. "If I could, I'd tell them never to eat collards again," says the appropriately lean Mr. Wilson, as he surveys gossiping gaggles of...