Energy bars, granola bars, snack bars, nutrition bars, diet bars, protein bars, meal- replacement bars...whatever you call them, the bar you want depends on what you want it to do for you. Since the ingredients, calorie counts, fat grams, and vitamin and mineral values are all over the map, to get what you need you have to know what to look for. Here's a cheat sheet.

Fuel a Long Workout Energy bars were originally invented to deliver a massive concentration of carbs to fuel marathoners or replenish a runner afterward. Yes, you could carry a potato in your pocket, but a bar that's high in complex carbs and fiber too (at least 3 grams) will create less havoc in your blood sugar and the benefits will last longer. Look for one like the Oatmeal Raisin Clif Bar that has about 70 percent of its 240 calories coming from carbs, plus 5 grams of fiber.

Help Build Muscle First, look for 15 to 35 grams of high quality protein-from whey, soy, casein and/or egg-to give your body the building material needed to repair muscle fibers. Skip bars containing "hydrolyzed proteins," made from mysterious animal parts. Next, check the fat, especially the saturated fat. You want least possible sat fat, and definitely no more than 3 grams. One good choice: Nutrilite Trim Advantage Caramel Vanilla Protein Bars, with 22 grams of protein but only 1 gram of sat fat.

Replace a Meal The built-in calorie and portion control of meal-replacement and diet bars can help you lose weight, say researchers...as long as you really do replace one meal with one bar. As for nutrients, most meal bars have plenty of carbs and are usually fat-conscious, but check their protein. You need 50 grams or more a day, depending on how active you are. Some low-cal meal bars don't have much-for instance, Slim-Fast Meal Options Breakfast & Lunch Bars (140 calories) have only 5 grams of protein. For about 100 more calories, you can get three times the protein (15 grams) in a Nutrilite Trim Advantage Meal Replacement Bar.

Have a Healthy Snack Think "small is beautiful." A snack bar should be smaller than a meal-replacement bar, and you need to watch the fat and sugar (stay below 18 grams). Steer clear of those made with high fructose corn syrup (HFCS), which has all sorts of health and weight-gain issues. Some snack bars are as calorie-packed as a candy bar, so it's worth searching out a truly low-cal one like PowerBar 110 Plus Pria. The various flavors weigh in at only 110 calories.