Overwhelmed by the sheer number of options for nutrition bars? Molly Kimball, a registered dietitian, recently wrote about navigating your way through the sea of nutrition, energy, snack, protein and meal bars:

There's no easy answer as to which bar is best. That depends on your nutritional needs, and why you're reaching for one.

If you want a snack that will keep you feeling fuller longer, try a bar that's higher in protein and lower in sugar. But if you want a bar that will be rapidly digested to fuel your exercise, or to help your muscles recover quickly after a workout, you'll want a bar that's lower in protein and fat (both of which can slow digestion).

To put the

protein

numbers into perspective, an egg has about 7 grams of protein, and a 3-ounce chicken breast has about 20 grams. So a Special K Protein Meal Bar with 10 grams of protein? Not so much a meal. But the Think Thin bar with 20 grams? At least you've got a shot that it'll hold you till your next meal or snack.

You won't find many truly

low-carbohydrate

nutrition bars on shelves. A few bars (Oh Yeah Protein Wafers and Power Crunch Bars) have just 8 to 10 grams of total carbs, but most bars have at least 12 grams (about what you would get in a slice of low-calorie whole wheat bread), and some have as many as 45 grams of carbs.

The

sugar

content can vary just as widely, from zero grams to 30-plus grams -- the equivalent of more than seven sugar packets. And the word sugar may not even appear in the ingredient list; it's often seemingly healthful ingredients (think brown rice syrup and evaporated cane juice) that contribute a majority of the sugar content.

Scan the label of the higher-protein, lower-sugar bars, and you'll likely see sugar alcohols listed in the nutrition facts. Sugar alcohols (such as maltitol and sorbitol) are sweeteners that provide fewer calories than sugar (0.2 to 3 calories per gram, compared to sugar's 4 calories per gram). They result in less of an impact on blood glucose and insulin levels, but they can cause gastrointestinal upset (usually gas or a laxative-like effect) in some people.

And look out when it comes to

fiber

content, since the nutrition facts can be a little misleading. Some bars may boast high fiber, along with a laundry list of whole grains, nuts and seeds in the ingredient list. Others, however, simply add isolated fibers such as chicory root (also called inulin) to boost the fiber count on the nutrition facts label. These ingredients aren't bad; they're just plant-based substances that we don't digest. But they're not the belly-filling whole grains that we usually associate with fiber. And they don't provide the nutritional benefits of real whole grains.

Saturated fat

is one potential drawback of many nutrition bars, with some containing as much as 6 grams of saturated fat per bar -- nearly one-third of the recommended upper limit.

Finally, there's the

calorie

content to consider. Nutrition bars can range from 100 calories to more than 400 calories, so be sure that you won't be adding unnecessary calories by incorporating a nutrition bar occasionally. Although individual calorie needs vary greatly, 100 to 200 calories is generally appropriate for a small snack, 200 to 300 calories for a more substantial snack, and 300-plus calories for a large snack or a small meal.

And here's the thing: no one really needs to eat a nutrition bar; they don't give us anything special that real food can't provide. They're for convenience only, good in a pinch when you need a grab-and-go snack, and (usually) a better option than a candy bar.

Molly Kimball is a registered dietitian in New Orleans. Her column appears every Friday in the Times-Picayune Living section. Click here to go directly to her article, posted on June 18, 2010.