The stomach digests carbohydrates faster than proteins (the liver processes fats). Simple carbs (sugars) break down the fastest, making their fuel available for quick energy bursts.
Nutrients pass through the wall of the small intestine and into the bloodstream. The small intestine starts absorbing water about 5 minutes after you drink it.
The large intestine sucks the rest of the water out of undigestable food.
The Experts: Brenda Braaten and Claudia Carberry
Braaten is a registered dietitian, AT and Long Trail alum, and author of Pack Light, Eat Right.
Carberry, a registered dietitian, runs a fitness website called Charge the Trail.
When you’re heading out for a weekend backpacking trip, how you eat doesn’t really matter. “You can do everything wrong and still enjoy yourself,” Braaten says. Hike for longer than two weeks without proper nutrition, however, and you risk depleting both the glycogen that’s stored in your muscles and liver and the B vitamins crucial for generating energy. You need to constantly take in nutrients to replace the ones you’re burning, or your body will revolt.
Fuel Up for Big Miles
Low-intensity but long-lasting activities such as hiking run best on a slow-burn fuel like fat. Instead of relying on carbs for energy—your body’s default—you can shift your system to burn fat first. Here’s how, says Rich Rife of Mountain Fitness Research: Exercise after a long period of fasting, like first thing in the morning, and train at a low heart rate zone to keep out of the anaerobic state, during which the body races through glycogen stores (carbs stored in the muscles and liver). Afterward, eat high-fat meals and, after 12 to 16 weeks, your body will choose fat as its primary fuel for low-intensity efforts, unlocking go-longer energy.
Hydrate for Hiking
Drink up: Appropriate fluid levels keep the muscles and fascia, the connective tissue that encapsulates muscles, supple and in working order. “If you’re dehydrated, muscle fibers and fascia are not going to slide correctly. And that’s where cramps can set in,” says McCall, the master trainer. Monitoring the color of your urine is a simple way to ensure you’re drinking enough water; if your pee is darker than lemonade, drink more. But unless you’re sweating excessively, lay off the sports drinks, most of which contain twice the concentration of salt your body needs and can actually dehydrate you by recruiting extra water to process the stuff. If you must slug a Gatorade, dilute it by half.
Embrace the Fat
Long-distance hikers need up to 4,500 calories per day. Make fat 40 percent of your diet by incorporating fat-heavy foods like olive oil, macadamia nuts, peanut butter, and cheddar cheese into your meals.
Common Nutrition Problems
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.
The Problem Hitting the wall, running out of gas, whatever you call it, “that feeling of bonking is really you running out of glycogen stores,” Carberry says, and is caused by working too hard for too long. “Our bodies can only store about 500 calories in the liver and 500 to 2,000 calories in the muscles,” she says.
The Fix For starters, get in shape; fit muscles can store more glycogen than untrained ones. On high-intensity outings, snack on regular but small doses of carbohydrates—about 15 to 30 grams every hour—to replace glycogen. If you try that and you’re still running out of juice, slow down. Lower intensity work will shift your system back to burning fat for fuel, leaving your glycogen stores more intact.
The Problem You wolf down a cheeseburger, fries, and a big ice cream sundae but it goes right through you. “Digestive enzymes are ‘negotiable’ in your body’s sense of survival,” says Braaten, meaning long bouts of exercise can alter the composition of your gut flora. The gross result: steatorrhea, a foul, loose stool that contains abnormally high amounts of undigested fat. In short: Your body, under stress from your hike, is evacuating all the good stuff.
The Fix Instead of eating a pile of fatty food at once, give your body extra time to process what you’re taking in. “You’ve got to space it out,” Braaten says. Take two to three hours between treats. Bonus: You now have an excuse to eat dessert with breakfast.
Pro Tip: Snack Smart
Braaten recommends packing slices of fruitcake. At more than 120 calories per ounce, it’s one of the most energy-filled, ready-to-eat foods available. Bonus: Its legendary density means it takes up minimal pack space.