PowerBars, Clif bars, Luna Bars, Met-RX Bars. A plethora of energy bars awaits you at every convenience store, each bar boasting of its ability to enhance performance. You can find a bar for every diet style--kosher, low carb, vegan, organic--and for every exercise need--pre-exercise fuel, recovery, muscle growth. But do you need them?

Yes, you can spend a small fortune on these prewrapped bundles of energy, thinking they offer magic ingredients (not true). "Energy" simply means "provides calories" and not "will make you feel more energetic." No research, to date, proves that a specific brand of energy bar contributes to performance enhancements beyond that found in the energy from oranges, Wheaties, and even chocolate bars (the original energy bar, right?). Granted, the wholesome bars made from real oats, nuts, and fruits (such as Clif bar, PowerBar Harvest, Odwalla Bar) are nutritionally preferable to chocolate bars, but do you really believe a Marathon Bar or Detour Bar is anything more than glorified candy?

Energy bars are big business. That's why Nestles bought PowerBar and Kraft Foods bought the Balance Bar brand. These major food companies know that today's consumers want convenience at any cost. Energy bars are both convenient and costly! You'll have to fork over at least one dollar, if not two, to buy most energy bars.

The following information on the pros and cons of energy bars can help you decide how much (if any) of your food budget you want to dedicate to these popular snacks.

* Energy bars are ready-and-waiting to be consumed. No mess, no preparation, no refrigeration. In today's eat-and-run society, when meals are a rare occurrence in a busy schedule, an energy bar suits the need for many hungry athletes who seek a hassle- free, somewhat nutritious alternative to vending machine snacks or a missed meal. The bars have a long shelf life, so you can stock them in your desk drawer or cupboard for a steady supply.

While a bar or two a day is unlikely to be harmful, if your wastebasket or car floor is littered with energy bar wrappers, think again. You're naive to think this processed item can replace a whole food. Rather, bars commonly displace apples, bananas, and other fruits that optimize health. If you resort to an energy bar for a meal replacement, at least try to eat some real food alongside, such as a yogurt and an apple or a (lowfat, decaf) latte and raisins. Also, try to choose a bar that has 10 to 15 grams of protein, such as a Hooah Bar (designed by the U.S. military to be "soldiers' food." They are available at WalMart, amazon.com, CVS, etc.).

* Energy bars are portable. You can easily tuck these compact and lightweight bars into a pocket or gym bag for preplanned or emergency food before, during, and after a workout. The bars don't crumble, but take heed: some melt in the heat, or become unchewable in the cold.

* Energy bars facilitate pre-exercise eating. The energy bar industry has done an excellent job of educating us that pre- exercise fuel is important for optimizing stamina and endurance. The associated energy boost likely does not result from magic ingredients (chromium, anti-oxidants) but from eating 200 to 300 calories. These calories (which usually include some form of sugar) clearly fuel you better than the zero calories you would get from not eating. But note that calories from tried-and-true graham crackers, bananas, and granola bars are also effective pre-exercise energizers.

* Instead of relying solely on the carbs in your pasta dinner the night before a hard workout, you can stay well fueled during the session by consuming about 0.5 gram of carbohydrate per pound of body weight per hour. This comes to 200 to 300 calories (as tolerated) for most athletes--exactly what an energy bar offers. Just be sure to drink plenty of water. Your body needs both fuel and fluid to perform well.

* Most energy bars claim to be highly digestible. One could debate whether energy bars are easier to digest than standard food, because digestibility varies greatly from person to person. I've heard some athletes comment about how a PowerBar settles heavily in the stomach, whereas others swear it is the only food they can tolerate during exercise. As with all sports snacks, you have to learn through trial and error during training what foods work for your system and what foods don't. Do not try this pricey treat for the first time before a special event, such as a marathon, only to discover it causes intestinal discomfort.

* One key to tolerating energy bars is to drink plenty of water along with the bar. Energy bars have a very low water content to make them more compact than fresh fruit, for example, which has high water content. But this low water content means they can settle like a lead brick.

* While the "all natural" and "organic" energy bars have no additives, they also have no vitamins and minerals added to them. This means they tend to smell and taste better than the fortified brands. But they lack the nutrition boost that can help athletes who, let's say, avoid red meats and have an otherwise low intake of iron (needed to prevent anemia) and zinc (enhances healing). A simple compromise is to enjoy a variety of energy bars.

* Energy bars are expensive. A PowerBar costs $0.58 per 100 calories, as opposed to Fig Newtons, $0.24 per 100 calories, or, better yet, Nature Valley Granola Bars, $0.15 per 100 calories. Cost aside, the E in Eating is for Enjoyment; just be sure you enjoy your energy source!

Sports dietitian Nancy Clark, MS, RD counsels casual exercisers and competitive athletes at her private practice in Healthworks, the premier fitness center in Chestnut Hill, MA (617) 383-6100). Her Sports Nutrition Guidebook ($23), Food Guide for Marathoners ($20) and Cyclist's Food Guide ($20) are available by sending a check to PO Box 650124, West Newton MA 02465 or via www.nancyclarkrd.com.