Liquid vs. Solid
By Monique Ryan
You wouldn't dream of heading out for a tough training session without some carbohydrate support, most likely in the form of your favorite sports drinks for a hydration boost as well. But now triathletes have a full menu of more solid carbohydrate choices in the form of gels, blocks, energy bars and even real foods that they can consume when training and racing. While a semi-solid or solid nosh often seems to just hit the spot and beat the bonk, none of this matters unless these opaque carbohydrate forms are easily digested and improve performance.
What we know about carbohydrates and training
Blood glucose boost
The benefits of consuming sports drinks during training are well established. Blood glucose levels are maintained by your liver glycogen stores both at rest and during exercise. When you are not training, the majority of blood glucose fuel is used by your brain and central nervous system. But during exercise, your muscles significantly increase their use of blood glucose, especially as your muscle glycogen stores become depleted during extended training sessions. When your blood glucose drops you may experience muscle fatigue and find your pace decreasing or experience symptoms of hypoglycemia such as poor concentration. Consuming carbohydrate during exercise maintains blood glucose levels and allows your training session to proceed at the planned pace.
The potential amount of carbohydrate you can burn for fuel during exercise is related to the carbohydrate mix in your squeeze bottle. When you consume a drink that has only a single carbohydrate source, such as glucose, the maximum rate of carbohydrate that you can burn is 1 g per kilogram per hour. Adding more carbohydrates to the mix increases the rate of carbohydrate burning. With two carbohydrates in the mix, such as glucose and fructose or glucose and sucrose, you can burn about 1.3 g/kg per minute. Having a mix of glucose, fructose and sucrose pushes carbohydrate burning even higher to 1.7 g/kg per hour. By consuming several carbohydrate sources at one time, your body can use all the non-competing opportunities available to absorb each carbohydrate source.
Burning more carbohydrate per hour is a good thing and raises the potential to maintain exercise performance, but only if you develop effective strategies for consuming these carbohydrate portions, and tolerate the mix. Having a carbohydrate-electrolyte solution with two or three carbohydrate sources also enhances fluid absorption, and it is essential that your fueling strategies don't compromise your hydration. Sports drinks with multiple carbohydrate sources are effective for fueling and hydrations, but gels, blocks, beans, and carbohydrates foods add variety and a quick carbohydrate surge during swim practice, hard rides, and long runs.
Despite the fact that the solid carbohydrate sources are more concentrated than sports drinks and could empty from the stomach more slowly, several studies indicate that they do increase blood glucose levels, improve performance, and are well tolerated. Let's briefly take a look at some of these study results.
Some early studies utilizing a sports bar have compared liquid to solid carbohydrate during endurance cycling followed by a performance test. When similar amounts of carbohydrate were consumed as liquid, solid, or in combination, time trial performances were similar.
More recent studies have tested the effects of consuming gels and beans. One study had subjects cycle for 80minutes at 75-percent VO2 max, followed by a 10 kilometer time trial. Separate trials during which subjects consumed sports beans, gels, sports drink, with carbohydrate intake at 0.6 g/kg per hour, or consumed water before, during, and after exercise were conducted. There were no significant differences in blood glucose levels between all the treatments, but of course all of them were higher than the water trial. Time trial results indicated that all carbohydrate forms were equally effective in improving cycling time trial performance over water. Subjects also consumed a standard pre-race diet one to two hours before the test trials.
Another set of studies presented at the American College of Sports Medicine in Indianapolis this past May measured gastrointestinal tolerance of carbohydrate gel consumption during running. In one study, both male and female runners and triathletes completed a 16 km field test run as fast as possible on two occasions. During one, they consumed a gel at a rate of 1 g per minute, or 1.4 g per minute with water. A score rating for gastrointestinal problems were on the low end of the scale for both test doses. Researchers found no differences in tolerance between a gel providing glucose only, and one providing both glucose and fructose.
Choosing your carbohydrate form
Each form of carbohydrate offers some advantages to a triathlete and some forms may be more appropriately used for certain types of training sessions and race distances. Sports drinks are truly the main course for any race distance as they provide fluid, carbohydrate, and sodium, with some providing higher levels of sodium for the salty sweater and long-course triathlete at risk of sodium depletion. Understanding your fluid needs and optimizing fluid intake during training and racing, also ensures that your stomach will continue to empty at a regular rate, as dehydration can slow the rate of stomach emptying. To easily empty from your stomach, carbohydrate must also be in a liquid or semi-liquid state, so sports drinks also fit well.
Solid carbohydrate sources are relatively easy to carry, as gels, blocks, and beans can handily fit into pockets, and provide variety in taste and texture. They also hit the spot when hunger sets in during a workout or race and easy to carry. Drinking water whenever you consume these products is essential. This not only aids in digestion, but also ensures adequate hydration. Most carbohydrate solids do not provide the levels of sodium seen in sports drinks, so don't needlessly decrease your sodium intake during training and racing.
If you do consume some solid items during training, start drinking and eating within 30 minutes after training and consume fluids and solid products at regular intervals to maintain blood glucose levels and prevent gastrointestinal problems. Depending on the product used, thirty-two ounces of a sports drink provides about 50 g of carbohydrate, as does one and a half to two gels, six carbohydrate blocks, and one energy bar. For long distance triathletes, adding a gel, block, or bean to your sports drink mix can up the carbohydrate amounts to an effective 1.7 g/kg per hour. Just experiment with sports drinks and products and determine the protocols that work best for you regarding energy levels and tolerance.
Monique Ryan, MS, RD is the author of Sports Nutrition for Endurance Athletes, 2nd edition (VeloPress 2007). Click here to view more about the book or purchase. She was a member of the Athens 2004 Performance Enhancement Teams for USA Triathlon and USA Cycling Women’s Road Team. She is owner of Personal Nutrition Designs and offers her sports nutrition “E Program” at www.moniqueryan.com.