THE PROBLEM After weeks on the trail, your legs are shriveling into toothpicks, and hiking is starting to feel harder than it used to. “When we lose weight, we burn muscle as well as fat,” Carberry says. “Over time, that is going to decrease strength and endurance on the trail.” THE FIX Make sure you’re eating enough protein, especially men (if calories are limited, men burn through muscle mass faster than women). While protein isn’t a significant source of energy, it’s important for repairing your stressed-out muscles. You need at least four servings a day of high-quality protein (about 1 gram per kilogram of body weight daily). Beef jerky, beans, nuts and seeds, cheese, and powdered milk are all excellent sources of protein.