If you are curious about how to best fuel for endurance exercise, here are some tips presented at the 27th Annual SCAN (Sports Nutrition group of the American Dietetic Association) Symposium, April 2010. The information was presented by Asker Jeukendrup PhD, Professor of Exercise Metabolism-University Birmingham in England and Nancy Rodriquez RD PhD, Professor of Nutritional Sciences-University Connecticut.
Athletes commonly wonder what's best to eat during long runs, bike rides or other exercise that lasts more than 60 to 90 minutes. The answer depends on your personal tolerance. Some athletes enjoy the convenience of engineered sports foods such as Clif Chomps, PowerGels and Sports Beans. Others prefer the taste (and price) of standard supermarket foods, such as Fig Newtons, dried pineapple and gummy candy. All are equally effective. And because we're talking about survival more than good nutrition during endurance exercise, you need not tsk tsk yourself for enjoying candy. That's what your body wants--sugar! (FYI, gels and sports drinks are also just sugar.)
Does it matter if you get your energy from an energy bar as opposed to a sports drink?
No. Both solid foods and liquids (i.e., sports drinks) get burned at the same rate when you are exercising at a pace you can maintain for more than half an hour. Your job is to experiment during training to learn:
1) What settles best in your intestinal tract, and
2) What tastes best to you during extended exercise.
Consuming enough calories is more important than the form of the calories. With endurance athletes, research suggests the faster finishers consume more calories than the slower finishers. (Ironman Champ Chrissie Wellington consumed about 335 calories/hour when she won at Hawaii.) The challenge is to train the intestinal tract to manage that much fuel. If you are an endurance athlete, part of your training program is to practice your fueling so you can train your intestinal tract as well as your heart, lungs and muscles.
How much should you eat to maintain good energy when you're exercising for longer than 60 to 90 minutes?
The standard recommendation for fueling during endurance exercise has been to target 1 gram of carbohydrate per minute of exercise or 60 grams of carbs per hour, the equivalent of 240 calories. The research, originally done with just glucose, indicated consuming more than 60 grams glucose/hour offered no benefits. The body has a limited number of glucose transporters and can carry only 60 grams out of the intestines, into the blood and to the muscles.
More recent research indicates consuming as variety of sugars (that is, more than just glucose) allows more fuel to become available per hour. That's because different types of sugars (carbs) use different transporters. Generally, athletes consume more than just glucose. (Sports drinks, for example, tend to have glucose and fructose.) Let's say you eat a banana that consists of many different types of sugars and uses many different transporters. Your muscles will have access to more fuel (up to 90 grams of carbs/hour; 360 calories) than if you consume just one kind of sugar. Variety is a wise idea!