Energy bars have become the alternative fuel of the food industry. Designed with portability and convenience in mind, these bars are part of a $3 billion market that continues to reshape the snack lineup both on and off the trail.

There is no current evidence that energy bars provide a nutritional advantage over traditional trail foods, but it’s hard to ignore how incredibly compact and indestructible they are when crammed in your backpack. So, if you’re going to fork out the extra money and forgo gorp, bananas, and graham crackers, what should you think about when faced with all those bar wrappers at your local grocery store?

CARB COMBUSTION When you’re heading out on the trail, carbohydrates should be your first consideration: Bring loads of them. Carbohydrates are your main fuel source and a staple in most energy bars, but watch out for nutrition bars labeled “high protein,” “low carb,” or “meal replacement.” These products are designed to be everyday snacks, diet options, or lunch fillers. For the biggest bang, get bars that have at least 20 to 40 grams of carbohydrates per serving.

Simple carbs, found in fruits and processed sugars, convert to glucose and enter your bloodstream soon after consumption. Complex carbs, sugars, and starches found in whole grains, vegetables, and potatoes, take longer to break down but provide a more consistent fuel supply. Most bars will have a combination of the two, and some label how many carb grams are complex. Read the ingredients, too. High fructose corn syrup provides quick fuel while rolled oats are longer burning starches.

Fats and proteins are less efficient. Think of a carbohydrate as lighter fluid and fat or protein as a lump of coal. Dr. Dennis Bobilya, a professor of nutrition at the University of New Hampshire, says, “When a person eats fat, the fat doesn’t actually show up as a fuel source until it’s already been put around your waist. It’s not really helpful while you’re hiking.” Fats can provide benefits a day or two after you eat them, however, and are more calorie-dense than carbs. “For people who are going to be out for extended periods of time, it helps to have foods that have a reasonable amount of fat because you can pack so many more calories per pound of weight,” says Dr. Barry Braun, director of the Energy Metabolism Laboratory at the University of Massachusetts at Amherst.

Be careful, though. Many energy bars have a high percentage of saturated fat, which is a known contributor to an increased risk of heart disease. Try to have no more than 10 percent of your daily calories come from saturated fat and avoid trans fat or hydrogenated oil. As a broad guideline, look for bars that have up to five grams of total fat per serving and 10 grams of protein.

PREMIUM OR REGULAR UNLEADED? It may be tempting to choose one bar over another based on the smorgasbord of nutritional benefits offered, but Braun says, “The distinctions among the different energy bars is 99 percent marketing and 1 percent science.” Energy bars targeted to women, for example, market female-specific nutritional formulas, but Braun contends the “distinctions are so minor that they are inconsequential in terms of nutrition.”

The same holds true for bars including supplements like vitamin A or iron. If you’re taking a multivitamin, you don’t need a fortified energy bar. “Whatever is trendy and seems kind of hip or new is going to go into the bar, even though it really isn’t going to make any difference to you in how you feel, or your performance, or your happiness on the trail,” Braun notes. The energy boost you get after eating a bar is mostly because you just ingested a chunk of calories and carbohydrates.

Why not just take real foods? “That’s a reasonable point,” says Braun. “The thing about the energy bars is that they are remarkably convenient. A good portion size, they usually don’t crumble or fall apart; they’re easy to stick in your pack. Yes, a banana might be better, but after two days, a banana is not going to look like much in your pack.”