As you do hikes that are increasingly longer & steeper, you are obviously going to burn more calories. But not all calories burned are the same. For endurance-type activities, you burn calories from a combination of 1) fat reserves and 2) carbohydrate storage (glycogen). As the intensity of the hike increases, the % of energy burned from glycogen increases (although both fat and carb calories burn increase).

So, what happens when your “glycogen tank” of fuel runs out? Well, you’ll slow down and run more on fat calories. But you’ll feel like crap. And eventually, you need to refill your carb tank.

What do you think you want to fill your carb tank with? That’s right, foods high in carbohydrates. And to recover the energy quickly, you want to get the carbs in their fast. 

What sorts of carbs are absorbed quickly? Ones with high glycemic indices. Sugars, bread, etc… Foods you would normally think are bad to eat! The body increases its ability to handle and absorb these carbs during and post exercise, basically the opposite of being diabetic. You should take advantage of it.

In similar manner, do not eat food with a lot of fiber! Fiber slows down digestion, exactly what you don’t want! Give me that carb energy now!

So, what energy bars to take? Well keep in mind this whole carb loss issue is only important as hikes get really demanding. 

Let’s look at nutritional information of the two types John mentioned, and I’ll add two other contrasting options:

Chocolate Mint Clif Bar

Chololate Mint Crisp

GU Energy Gel

Italian Bread

You should compare everything on a per calorie level, i.e. if I eat 100 calories of each, what are the nutritional differences?

The GU Gel gives you the most pop per calorie, and with perceptibly no fiber! Italian bread performs better than either energy bars in terms of high carbohydrates and low fiber. There is a reason the GU is marketed specifically to endurance athletes, it has fast-absorbing carbs to help the athlete continue working at a high-intensity.

Am I recommending eating GU? No, I’ve never even tried it, and frankly, it doesn’t seem desirable. I’d rather have ‘real’ food. And guess what? Italian bread performs better than the two energy bars. Whole wheat bread might perform a little worse in that it will have more fiber, which you don’t want. Now, I eat energy bars on hikes, but I’m generally not zapped on energy. If I was, and if you are, it’s time to start cutting a loaf of bread!