<body><h1>Carbohydrate Supplementation</h1><p> &nbsp;Of the three classes of nutrients (fats, proteins, and carbohydrates), carbohydrates are the most active source of fuel during exercise. Carbohydrates in their most basic form are simple sugar molecules called monosaccharides. The most common monosaccharides are glucose, galactose, and fructose. Larger carbohydrates are made up of two or more monosaccharides in a chain, referred to as disaccharides, trisaccharides, or polysaccharides depending on the number of sugars. Carbohydrates are broadly categorized as either simple or complex, depending on the length of these sugar chains. The body must digest carbohydrates down to their monosaccharide forms before they can be absorbed and utilized for energy.</p><p> &nbsp;Glucose is the primary monosaccharide fuel source in human metabolism. While blood glucose can be utilized immediately for energy, it may also be converted to glycogen for later use. Glycogen, which is stored mainly in the muscles and liver, represents the body’s principle energy reservoir during anaerobic exercise. It is also important to performance in endurance (aerobic) activities. The level of stored glycogen will vary depending on size, training status, and diet. We humans typically store about 300-400 grams of glycogen in our muscles, and another 80-100 grams in the liver.9 This may be considerably higher in athletic individuals with significant muscle mass and training. Glycogen stores are usually sufficient to provide energy for 90-180 minutes of exercise at moderate intensity.10 High intensity exercise may deplete glycogen stores within 30 minutes. Once these glycogen stores are depleted, a significant decrease in performance will result, as the body will be forced to rely upon less efficient sources of fuel.11</p><p> </p><h2> &nbsp;THE GLYCEMIC INDEX</h2><p> &nbsp;The glycemic index is a system of categorizing foods based on the impact they have on blood sugar levels. It was developed to help diabetic patients better control their blood sugar levels through diet. The main factor dictating where a food fits in this index is its rate of digestion. Slower digesting foods and carbohydrate sources tend to produce lower peaks in blood sugar, and are considered less “glycemic.” The glycemic index gives each food a glycemic rating depending on its propensity to increase blood sugar. This GI rating generally ranges from 0 (no blood sugar response) to 100 (maximum increase), although certain rapid-digesting carbohydrates are listed above 100 on some glycemic index scales. Foods with a GI rating of 55 or below are considered low GI. A GI of 56-69 is considered moderate, and 77 or above high.</p><p> </p><p> &nbsp;By extension of their less dramatic effects on blood sugar levels, foods with a lower glycemic rating tend to produce lower levels of peak insulin secretion. This has implications beyond just the management of diabetes. For example, high GI foods tend to increase the likelihood of body fat retention, as insulin is involved in nutrient (fat) storage.12 Those wishing to reduce body weight usually find dieting more successful when low or moderate GI foods are consumed instead of sugars. Excess blood sugar and insulin elevations can also have deleterious effects on health. Diets high in simple sugars are not advised, and are associated with various diseases including metabolic syndrome, diabetes, cancer, and heart disease.13,14 There are many instances, however, when athletes may also find advantages to using high glycemic carbohydrate sources. </p><p> &lt;div id=’imgblock’&gt;&lt;img data-pointer=’6915’/&gt;&lt;/div&gt;</p><h2> &nbsp;CARBOHYDRATE SUPPLEMENTATION BEFORE EXERCISE</h2><p> &nbsp;Carbohydrate supplementation before exercise may help preserve muscle glycogen stores and extend muscle endurance. Supplementation will have its greatest impact if muscle glycogen stores are low at the start of exercise, and may not even be necessary if the exercise duration is short. Effective carbohydrate sources for pre-workout supplementation may include either high GI or low GI carbohydrates, as both seem to support training equally provided that blood glucose is maintained. Drinks containing simple carbohydrates are most common, and no individual sugar is considered to be more advantageous over others. For example, one study found similar levels of performance during a 10 km run when subjects consumed a drink containing fructose, glucose, or a sugar/glucose blend before the event.18 While recommendations often vary, the consumption of 30-60 grams of a simple carbohydrate blend 30-60 minutes before exercise is usually sufficient.</p><p> </p><h2> &nbsp;CARBOHYDRATE SUPPLEMENTATION DURING EXERCISE</h2><p> &nbsp;The supplementation of carbohydrates before exercise may not be sufficient to sustain blood glucose concentrations throughout the full period of activity. It may be necessary to supplement carbohydrates during exercise, especially if the intensity is high, or the duration is going to exceed one hour. The importance of such a supplement may also increase if no preworkout carbohydrate drink has been consumed. Given the need for rapid replenishment, the carbohydrate drink to use during exercise should contain a moderate dose of easily digested high GI carbohydrates such as glucose (dextrose), sugar, and maltodextrin.</p><p> &nbsp;Glucose appears to be effectively absorbed through the small intestine at a rate of about one gram per minute.19,20 Intakes above this level may cause gastrointestinal distress, which can interfere with performance. It is generally advised to drink 7.5-15 grams of simple carbohydrates every 15 minutes during exercise, or a total of 30-60 grams slowly each hour. Studies also show that the addition of protein, essential amino acids, or branched-chain amino acids can reduce protein catabolism compared to the use of 6-15 grams of protein per hour may be adequate.</p><p> </p><h2> &nbsp;CARBOHYDRATE SUPPLEMENTATION AFTER EXERCISE</h2><p> &nbsp;The window immediately after exercise is considered the most crucial for nutrient uptake and recovery/growth. The resynthesis potential of glycogen is at its maximum during the first 30-60 minutes after exercise, and is significantly elevated for two hours.21 During this time, the supplementation of high GI carbohydrate sources is advised to maximize glycogen retention. Studies show that glycogen levels can be replenished to near baseline levels within 24 hours when the post-exercise recovery window includes optimal carbohydrate consumption.22 They also show that if sufficient carbohydrates are not supplied within two hours of training, glycogen resynthesis is drastically slowed, and replenishment may take much longer.23 Maximum glycogen replenishment has been noted when high levels of carbohydrates (1-1.85 g/kg/hour) are given every hour for five hours post training.24,25</p><p> &nbsp;Insulin sensitivity, amino acid transport, and protein synthesis potential in the muscles are also intensified during the post-exercise recovery period.26,27,28 Studies show that a combination of protein and carbohydrates during this period maximizes protein synthesis rates and the retention of glycogen, and minimizes protein catabolism.29,30 The exact needs of the athlete will be dependent on the type of activity, the training status, individual metabolic factors, and the level of exercise intensity. Those undergoing low to moderate intensity exercise may find the consumption of 30 grams of carbohydrates and 10-20 grams of protein during the first two hours after exercise to be adequate. For those in high intensity training or bodybuilding programs, a minimum intake of 100 grams of carbohydrates and 25-50 grams of protein during the first two hours after exercise is usually recommended. </p><p> </p><h2> &nbsp;CARBOHYDRATE LOADING (PRIOR TO ENDURANCE COMPETITION)</h2><p> &nbsp;Total body carbohydrate storage can be maximized (beyond normal levels) during a process of carbohydrate loading. This is a common practice for endurance athletes, and typically involves the consumption of very high levels of carbohydrates for up to one week prior to an endurance competition. They may also employ a period of carbohydrate restriction and depletion for five to seven days prior to the loading phase. There is, however, no solid evidence that the practice of pre-depletion is beneficial.31 For peak glycogen loading it is recommended to consume 600-1,000 grams of carbohydrates per day for six days prior to competition.32</p><h2> &nbsp;“EXOTIC” CARBOHYDRATES</h2><p> &nbsp;In addition to the basic carbohydrate sources commonly used for the manufacture of glycogen support supplements such as glucose (dextrose), fructose, sugar (sucrose), and maltodextrin, some sport supplement companies heavily market the use of more exotic carbohydrate sources. These carbohydrates may have varying properties with regard to sweetness, rate of digestion, and glycemic effect. With regard to sports nutrition, however, the purpose of all carbohydrate supplements is to provide usable sugar for energy metabolism. It is questionable whether these exotic carbohydrates offer tangible ergogenic benefits compared to the use of basic carbohydrates. </p><h2> &nbsp;SUGAR ALCOHOLS</h2><p> &nbsp;Sugar alcohols are a unique family of carbohydrates that have combined sugar and alcohol components. Some sugar alcohols are found in certain plant species. Many others are synthetic derivatives of sugars. Many sugar alcohols are only partially absorbed, and therefore provide fewer calories per gram, and have a lower glycemic effect than sugar.33 Many also have reduced sweetness properties, however, and more may have to be consumed when attempting to replace natural sugar. Some sugar alcohols also have unique properties. For example, bacteria in the mouth does not readily consume xylitol. It is not associated with tooth decay, and makes a promising sweetener for use in chewing gums.34 It is unlikely that sugar alcohols offer any ergogenic advantage over the consumption of regular carbohydrates.</p><p> &nbsp;Trehalose is a disaccharide consisting of two glucose molecules connected by an alpha-1,1-glycosidic bond.35 This carbohydrate is unique in that it cannot be broken down in the mouth, and it only metabolizes to glucose by intestinal bacteria. Trehalose has a lower glycemic effect than most basic sugars (GI 67), and is promoted in sports nutrition as a slow digesting alternative for better glycogen replenishment. Studies do not support this claim, however, and suggest that trehalose may actually be inferior to glucose for supporting exercise performance.36 It is presently unknown if trehalose offers any ergogenic advantage compared to the consumption of regular carbohydrates.</p><p> &nbsp;Waxy Maize Starch is a high molecular weight starch extracted from certain plants such as corn and rice. It is especially high in amylopectin, a highly branched polymer of glucose. Waxy maize starch is sometimes promoted as a rapid source of glucose for the muscles, enabling a higher level of glycogen resynthesis. Studies, however, show this starch is actually slower to digest and peak (glucose) in the blood than high GI carbohydrates such as a maltodextrin and sugar.37 Waxy maize starch may offer some value as a steady carbohydrate source, but does not appear at this time to have any special properties with regard to glycogen replenishment after exercise.38 It also does not appear that waxy maize starch has an ergogenic advantage compared to the consumption of regular carbohydrates.39 Vitargo is the brand name for a patented high molecular weight starch fraction that is obtained from certain plants. Although it is derived from waxy maize starch, it is considerably different from this carbohydrate source. Vitargo appears to have the benefit of fast gastric emptying, which means that it leaves the stomach and enters the small intestine (where it can be absorbed) much faster than glucose or other common sugars.40 Studies have also shown that Vitargo causes a much higher retention of glycogen (+68%) two hours after exercise compared to the use of maltodextrin and dextrose.41 After four hours, however, there are no significant differences between carbohydrate sources. Vitargo appears to be a promising carbohydrate for supplementation, especially when the rapid replenishment of glycogen after exercise is required.42 It is, however, unknown if the regular use of Vitargo offers any ergogenic advantage compared to the consumption of common replenishment carbohydrates such as dextrose, sugar, fructose, or maltodextrin.</p><p> </p><p> &nbsp;</p><p>&nbsp;</p></body>