Howdy All
I apply the nutrition recommendations for endurance and ultraendurance sports to hiking. Research indicates that consuming carbohydrate before and during endurance exercise improves performance -- the athlete can maintain high intensity exercise longer and/or sprint harder at the end.
General observations on research findings with endurance athletes:
1) Liver glycogen (source of blood glucose) is nearly exhausted after an overnight fast. Taking in a carbohydrate-rich meal or snack before an early morning hike helps to prevent hypoglycemia (bonking) on a hike lasting over several hours.
For people who have difficulty eating before an early morning hike (myself for example), a semi-liquid meal such as oatmeal, yogurt or an instant breakfast drink is tolerated better than soilds. I eat a carton of yogurt an hour before hiking.
2) Consuming carbohydrate during exercise supplies energy for the muscles when they're running low on glycogen. From a performance standpoint, there's no difference between liquid (sports drinks, gels) and solid carbohydrate (energy bars, food). Consuming 30 to 60 grams of carbohydrate each hour (120 to 240 calories) improves performance (helps you maintain your hiking pace longer).
Between my one gel an hour and Gatorade, I'm consuming 30 to 60 grams per hour.
Individual tolerance and preference determines what you can eat. While climbing, my gut can only handle gels and a sports drink. Hard or chewable candy works well instead of gels for many people. I've hiked with people (usually large guys) who can scarf down pretty much anything without experiencing gut distress.
The greater the exercise intensity, the lower the ability to absorb calories as blood is diverted from the gut to the muscles.
High fat foods (nuts, cheese, meat) delay stomach emptying and are more likely to cause gut distress. However, protein and fat also provide satiety. I recommend experimenting with different foods while hiking to find out what you can tolerate and enjoy. Most people find they experience taste fatigue on very long hikes, so it helps to have different foods.
The length of the hike. temperature, and pace also affect what you can tolerate and enjoy. As Tomcat pointed out, I recommend not trying any new fluid or food when you're attempting a major climb such as the full C2C.
3) The only way to really know how much to drink is to determine your sweat rate range in different environmental conditions. On Skyline, closely matching fluid intake with fluid loss is necessary to prevent heat illness as well as maintain performance.
Whether you use water or a sports drink is a matter of personal preference. If you carry water, you want to also have a source of sodium such as salty snacks, salt tablets, or higher sodium carbohydate gels. I find sports drinks convenient because they supply water, carbohydate, and sodium.
4) Consuming sodium helps to prevent heat cramps and hyponatremia (low blood sodium) during long, hot hikes. On average, people lose 800 mg of sodium per quart (2 lb) of sweat.
Hyponatremia can occur during endurance exercise lasting four hours or more such as triathlons or ultra runs when the person drinks more water than they're losing in sweat. Hyponatremia generally does not occur during hiking -- the exception being hiking the Grand Canyon where people over-drink on the way down.
5) The American College of Sports Medicine notes that atlhough caffeine is a diuretic, it does not contribute to dehydration. Research has shown that consuming 3 to 6 mg of caffeine per kg of body weight can enhance endurance.
Whether or not to use caffeine is entirely individual. I always have coffee in the morning (whether I hike or not). I find that I get a little "lift" from the caffeinated gels. However, if I use one every hour, I get nauseated.
6) I rest and eat a high carbohydrate diet the day before a hard hike such as Skyline, Whitney, or Vivian. This helps to ensure that my muscle glycogen stores are above normal for the hike. When I ran marathons, I ate a high carbohydrate diet and rested for three days prior the marathon to carbohydrate load.
Miles of smiles,
Ellen