One of the greatest challenges with low-calorie cooking is flavor. Without the fat, recipes can taste as if they're missing something. That's when chefs turn to zests: finely grated rinds of lemons, limes, oranges, and tangerines. Citrus zests have the bright flavor of the fruits, without the acidity. They contribute subtle undertones to dishes both savory and sweet, plus an additional benefit: many of the antioxidants found in citrus are concentrated in the fragrant oils in the rind. (Since pesticides tend to concentrate in the rind, choose organic fruits for zesting.) The recipes featured here show what a little zest can do to boost the flavor of light dishes. But don't limit yourself to these. Stir a teaspoon or two of zest into your own dips, soups, stews, and baking batters.