By Sheri Colberg, Ph.D., FACSM
Fluids, Sport Drinks, Gels, and More
Gatorade, PowerAde, All-Sport, Cytomax, GatorLode, Ultra Fuel, GlucoBurst gels, Power Bars, Clif Bars — with so many sport drinks, gels, and other sport-related supplements to choose from, how can you choose which one to use, if any? Let’s start by taking a closer look at sports drinks and other fluids. During exercise, a fluid that is a 5- to 10 percent carbohydrate solution (meaning that it contains 5 to 10 grams of carbohydrate per 100 milliliters of fluid) will empty from your stomach as rapidly as plain water does, can hydrate you effectively, and will provide you with carbohydrate. If you’re worrying about maintaining your blood sugars more than your hydration, choose one with a slightly higher carbohydrate content; not surprisingly, taking in a 10 percent carbohydrate sports drink has been shown to keep blood sugars higher than consuming a similar quantity of an 8 percent one.
You should use more concentrated solutions (above 10 percent) only before or after exercise because their emptying from your stomach is somewhat delayed. Fruit juices are usually more concentrated than 10 percent and should be diluted for faster absorption during exercise, but remember that their GI is usually lower than many other choices. You may also want to avoid juice for another reason: drinks with high amounts of fructose (fruit sugar) may cause abdominal cramps or diarrhea, likely because fructose is absorbed more slowly than glucose is and it pulls water into your stomach and small intestines when consumed in high concentrations.
As far as your hydration status is concerned, whether you can rely on a sports drinks or just plain water depends on how long your activity is going to last. During an exercise session of an hour or less, you can effectively maintain hydration with water alone, although athletes with diabetes may need the extra carbohydrate in sport drinks for blood sugar maintenance. You don’t need to worry about replacing electrolytes (like sodium, potassium, chloride, and magnesium) during shorter events because sweating doesn’t immediately unbalance them; sweat is more dilute than blood and contains less sodium and other electrolytes. For longer events, water alone will keep you hydrated, but taking in sports drinks or other substances with carbohydrate will prolong your endurance by preventing drops in blood sugars and providing your muscles with an alternative source of carbohydrate (besides muscle glycogen).
During extremely prolonged activities such as a full Ironman triathlon, you’ll need to replace electrolytes lost during the event, especially when you’re consuming lots of fluids. Otherwise, you may end up with a dilution of sodium in your blood that causes hyponatremia (low sodium levels), otherwise known as water intoxication. Symptoms include light-headedness, headaches, nausea, repeated vomiting, and malaise. For the most effective hydration, take in fluids before you start, during the activity, and afterward, but don’t go overboard on the amount, even if it contains some electrolytes. Too many sports drinks can cause water intoxication despite containing sodium and other electrolytes.
In general, fluids are best drunk cold and with less than 10 percent carbohydrate in them to promote faster emptying from your stomach. Ice-cold water will get into your body more rapidly than a lukewarm drink will, but taking in more than 500 milliliters at a time will slow the rate of emptying and increase your risk for hyponatremia. While exercising you must start drinking before you feel thirsty because thirst is not triggered until you have already lost 1 to 2 percent of your body weight in the form of water. Taking in a large mouthful (1 to 2 ounces, or 20 to 60 milliliters) at a time is usually sufficient. In summary, any drinks that you take in during exercise should ideally contain less than 10 percent carbohydrate, be cold, have a volume of less than 500 milliliters, and contain some replacement electrolytes (during exercise lasting longer than an hour).
The main benefit of taking in carbohydrate-based gels is that the quantity is measured (e.g., 15 grams) and they don’t require you to take in extra fluids if you already are sufficiently hydrated or at risk for hyponatremia. If they’re glucose gels like GlucoBurst, one gel packet equals almost four glucose tablets, and a gel may be easier to eat while exercising. For PowerBars, Clif Bars, and other sports bars, you take in some longer-lasting protein and fat along with the carbohydrate, which can help prevent your blood sugars from dropping as much later on during longer workouts or events. A comparison of some of the sports drinks, gels, and other nutritional products for diabetic athletes can be found in Diabetic Athlete’s Handbook.
Carbohydrate Loading: Effective If Done Right
Almost all athletes benefit from carbohydrate loading before long-distance events because they can then begin exercise with fully restored or even supercompensated glycogen stores. Traditionally, this loading technique consisted of three to seven days of a high-carbohydrate diet combined with one or two days of rest or a reduction in exercise volume, a method known as tapering. Your daily diet while loading should contain 8 to 10 grams of carbohydrate per kilogram of body weight, which is similar to the recommended intake for all endurance athletes. We now know that even a single day with a higher carbohydrate intake and rest or tapering can effectively maximize carbohydrate stores, so you don’t need to spend a week, or even as long as three days, overconsuming carbohydrate. So, to maximize your glycogen stores, all you really need is one day and a combination of rest, a carbohydrate-rich diet, and excellent blood sugar control throughout the day.
For carbohydrate loading to be effective for diabetic exercisers, your muscles must be able to take up enough glucose. The way to ensure the proper glycogen storage, and even supercompensation of stores in your muscles and liver, is to have sufficient levels of insulin when you take in carbohydrate to prevent hyperglycemia and promote glucose uptake. Consuming higher-fiber carbohydrate sources and those with a lower glycemic effect will help prevent an excessive rise in your blood sugars and will still be effective for loading. In fact, a recent study showed that poorly controlled diabetic exercisers can actually end up with higher glycogen stores when they maintain better blood sugar control by loading with less carbohydrate (50 percent of calories as carbohydrate instead of around 60 percent), so eating as much carbohydrate as the glycogen-loading scenarios recommend may be counterproductive for most diabetic athletes. For optimal liver glycogen stores, maintaining more normal blood sugars has also been shown to be the most effective strategy.
This column is excerpted from Diabetic Athlete’s Handbook
(released November 2008 from Human Kinetics), which contains essential exercise-related information and examples for Type 1, Type 1.5, and Type 2 diabetic exercisers. More information is available at www.shericolberg.com