Here's the good news: If you're hiking 10 to 20 miles (16 to 32.19 kilometers) per day, day after day, with a heavy pack on your back, you won't have to worry that an extra piece of pizza will go straight to your waistline. Then again, since you most likely won't be packing a pizza with you (not exactly transportable) and certainly won't be in a place where you can get a pie delivered, it's a moot point. But you will need food to fuel your body as you spend very long days exerting yourself on the trail.
Planning what to bring on a long-distance hike is a balancing act. On the one hand, trekkers need to have around 2 pounds (907.2 grams) of food per day, and it's always wise to have an extra pound or so just in case [source: Alt]. But the trick here is to be able to get all the calories you need while keeping the weight of the food to a minimum and ensuring that your breakfasts, lunches and dinners are easy to prepare. It's beyond doubtful that you'll have the energy to whip up gourmet meals after a 12-hour day going up and down mountains. Some food items that combine the benefits of easy portability, plenty of energy and little prep work include bagels, peanut butter, honey, macaroni and cheese, energy bars and freeze dried meals that can be whipped up by just adding boiling water.
Staying hydrated is just as important as being well nourished. To that end, long-distance hikers should drink at least 1 gallon (3.79 liters) of water per day [source: Alt]. Steve Silberberg, who runs a company called Fitpacking, which helps people get in shape by hiking, suggests bringing along a 3-liter hydration bladder. It allows people to drink continuously and conveniently so as to avoid dehydration. "When you become dehydrated, your performance and judgment suffer, leaving you susceptible to poor decisions, hypothermia, sun stroke, precipitous falls and weakened ability to get to shelter or rescue," Silberberg says. As a precaution it's wise to bring along devices for treating water to prevent giardia -- a parasitic infection that can cause nausea, fever and diarrhea -- in case you need to drink from a stream. A water filter or iodine tablets can make stream water potable.