After more than a year's delay, U.S. schools have a new government ruling aimed at snacks sold to students, in a move nutritionists say could figure prominently in the war against childhood obesity. The U.S. Department of Agriculture issued a “Smart Snacks in School” proposal Feb. 1, which includes provisions such as promoting availability of healthy snack foods with whole grains, low-fat dairy, fruits, vegetables or protein foods as their main ingredients.