By Ilana Katz RD

Athletes are well aware that carbohydrates are their main source of fuel, particularly during activity. This seems simple enough, however, the word carbohydrate itself opens a can of worms worth dissecting. Carbohydrates (carbs) are categorized as either simple or complex, and complex they are. Simple carbs, commonly known as sugars, occur in the form of either a monosaccharide (1 sugar unit) or a disaccharide (2 units). Complex carbs are polymers of simple carbs (many sugar units). These carbohydrate units are the functional ingredient in sports products, mainly drinks and gels. So the question becomes, “What carb is the right for me?” In reality, no major difference exists on athletic performance between the use of any one carb (fructose, maltodextrin, sucrose, glucose, dextrose, galactose). What does exist is differing absorption rates, levels of sweetness and thus appeal. To analyze how the sports product manufacturers decide upon the combinations of carbohydrates they use may answer the athlete’s question as to what is their drink/gel of choice to fuel thier athletic performance.

Athletes must choose a product whose absorption rate agrees with their individual gastrointestinal sensitivity. Factors that affect carbohydrate absorption rate include concentration, volume, solubility, and the Glycemic Index of the carbohydrate. Concentration is the energy content (calories) of the carbohydrate in solution. A small concentration of carbohydrate results in rapid travel from the stomach to the small intestine. Research shows that a 6 – 8% concentration of carbs has an optimal gastric emptying rate. Stronger concentrations in the stomach attract more fluids to the gastrointestinal system, and not only result in a bloated, uncomfortable, sluggish stomach, but simultaneously draw fluids away from their important function in muscle contraction…

The Glycemic Index (GI) measures how fast the carbohydrate of a particular food is converted to glucose and enters the bloodstream. Many athletes believe that consuming low glycemic carbs before exercise provides a long lasting source of fuel. However, research does not support this. Research does, however, support that consuming moderate to high Glycemic Index Carbs during activity raises carbohydrate availability and, therefore, enhances endurance and performance (1).

Fructose is a monosaccharide, has a unique digestive pathway, and is the preferred simple sugar that restores liver glycogen, a stored form of fuel. Fructose also has a fairly low glycemic index. Together with it being a sweetening agent, these qualities favor its use as a carbohydrate in sports products. Due its need to be metabolized by the liver, however, it has a slow absorption rate and sports drinks that contain mainly fructose may cause gastrointestinal distress. Thus, fructrose used alone is not the ideal carb for optimal performance.

Sucrose is absorbed more rapidly than fructose. It is a simple, easily digestible sugar with a mid-range glycemic index. Furthermore, its pleasant sweetness and palatability adds appeal. Consumers are often concerned that sucrose, being table sugar, causes weight gain. Certainly, in large amounts, as with any other sugar, sucrose may have an effect on weight, however, as an ingredient in a sports drink and consumed in moderation, it has positive qualities as a fuel source.

Maltodextrin, because of its complete solubility is an ingredient found in many sports nutrition products. Complete solubility leads to less risk of gastrointestinal distress. Maltodextrin is a polysaccharide with building blocks of glucose. Even though the bonds need to be broken for fuel availability, their digestion does not put undue stress on metabolic processes. The resultant glucose molecules then enter the blood stream immediately, therefore, providing an instant source of energy.

Dextrose is a simple sugar with a high glycemic index thus providing a rapid source of fuel. It is also known to stimulate gastric emptying as well as sodium reabsorption from the kidneys, rating high on hydration strategy. Dextrose may add appeal with its pleasant sweetness, and unlike fructose, dextrose requires no liver metabolizing before getting into muscles as a fuel. It is therefore a positive ingredient for sports products, however caution is recommended. Higher glycemic index carbs as the solitary ingredient may lead to a sudden high level of insulin causing rapid and possibly excessive transport of blood glucose into the tissues, resulting in low blood sugar.

Carbohydrates are are often used combination in sports products in order to balance their positive with their negative effects. High glycemic index carbs, such as glucose and dextrose may often be combined with lower glycemic index carbs such as fructose and galactose, a monosaccharide that is also not digestive intense. This combination reduces the high insulin response associated with high glycemic index carbs yet it is quickly absorbed. Fructose and maltodextrin are often found in combination. Fructose enhances the sweetness of the bland flavorless maltodextrin, and similarly, maltodextrin removes the unpalatable over sweetness of fructose.

Sports products often have fructose as an ingredient because of its unique digestive pathway. Alone, as mentioned above, it may induce gastrointestinal distress, however in combination, it enhances carbohydrate availability, when the other carbohydrates’ saturation levels are reached. It is thus best as a secondary carb source. The words “High Fructose Corn Syrup” a processed food component derived from fructose and glucose, are therefore, inevitable on a sports products ingredient list. This component is worth mentioning due to the negativity surrounding it and its perceived role in the obesity epidemic. This is unfortunate because any nutrients or foods consumed in unnaturally high doses, is the real reason for obesity (2).

Choosing your sports products can be very individual and athletes are advised to experiment with different products. Factors affecting choice may include duration, intensity, and climate (extreme conditions can alter the gastric emptying rate). Sugars provide fuel to working muscles. An optimal combination would be readily absorbed with an appealing taste. One mans sweet is another mans gastric issue, therefore, optimal carbohydrate fuel does not necessarily come from one sugar source but a preferred combination.

References:

1. Burke et al. Glycemi Index: A new tool in Sports Nutrition. Int J Sports Nutr. Dec 1998; 8(4), 401-15.
2. The truth about High Fructose Corn Syrup. www.poweringmuscles.com.