COMPLEX CARBOHYDRATES - A SUPERIOR FUEL COMPARED TO SIMPLE SUGARS
COMPLEX CARBOHYDRATES - A Superior Fuel Compared to Simple Sugars
Most everyone who is familiar with Hammer Nutrition fuels knows our uncompromising stance on the use of complex carbohydrates versus simple sugars for optimal fuel/energy production. In Endurance News #52 (http://www.hammernutrition.com/downloads/ENews/ENissue52.html) we ran an article (“Complex Carbs or Multiple Carb Sources – Which is Better?”) that discussed the results of research by the Dutch sport scientist, Asker Jeukendrup. To recap the article, the general conclusion of the studies showed that a blend of carbohydrates increased oxidation rates, which means higher amounts of energy were produced. In one of Jeukendrup’s studies he found that cyclists who ingested a 2:1 mixture of maltodextrin and fructose were able to oxidize up to 1.5 grams of carbohydrate every minute. In another study – using a mixture of glucose, fructose, and sucrose – oxidation rates peaked at 1.7 grams per minute. Both those results are pretty eye opening, considering that the majority of research on the subject has shown that complex carbohydrates allowed for 4.0 – 4.1 calories/minute, or approximately 1 gram/minute.
However, there’s more to the results that what first meets the eye and the key to our original article – our position regarding the studies as well as the companies that are jumping on the “multiple carb sources are better than complex carbs alone” bandwagon – was not to dispute the results of Jeukendrup’s published studies. The key to the article was whether or not the results of these studies would be applicable in faster-paced, longer-duration bouts of exercise. You see, if you look carefully at the studies you’ll note that the exercise intensity of the cyclists in the majority of studies was quite low, only 50-55% maximum power output, which I think we’d all agree is very much a recovery pace, if that.
To be blunt, at a leisurely 50% VO2 Max pace, athletes can digest cheeseburgers and pizza with no gastric issues. However, if the heart rate and core temperature is raised even to only 70% VO2 Max, the body must divert core accumulated heat from central to peripheral. This reduces the blood volume available to absorb ingested carbohydrates or whatever the athletes have consumed.
After two decades we have found that in the overwhelming majority of the athletes we’ve worked with – athletes engaged in typical 75-85% efforts and/or in multi-hour endurance events – the combination of simple sugars and long chain carbohydrates, and in amounts higher than 1.0 – 1.1 grams per minute (4.0 – 4.6 calories per minute), have NOT yielded positive results. They did, however, increase performance-inhibiting, stomach-related maladies.
Lowell Greib MSc ND explains that gastric emptying is a key limiting step in carbohydrate metabolism: “If your stomach can't empty the product (no matter what it is) you are going to get nothing from it except a huge gut ache and possibly lots of vomiting! Unless there is new research that I am unaware of, gastric emptying is directly proportional to the osmolality of the solution in the stomach. A long chain carbohydrate (maltodextrin) contributes less to increasing the osmolality than do disaccharides (sucrose, lactose, maltose, etc.).”
Augmenting Greib’s statements, Dr. Bill Misner writes, “Absorption rate and how fast the liver can ‘kick it out’ are limiting factors. No matter what you eat, how much or how little, the body provides glucose to the bloodstream at a rate of about 1 gram/minute. Putting more calories in than can generate energy taxes gastric venues, electrolyte stores, and fluid levels.”
Bottom line is not whether or not Jeukendrup’s published studies are disputable, but rather if these studies apply to faster paced, longer duration bouts of exercise. We do not believe this to be the case, which is why we do not recommend the use of multiple carbohydrate sources during exercise. Stick with complex carbohydrate fuels, and we guarantee you’ll see better results.
With that in mind, here is a portion of research regarding the superiority of complex carbohydrates as compared to simple sugars…
GLUCOSE POLYMERS [MALTODEXTRINS] EMPTY THE STOMACH FASTER THAN SIMPLE SUGARS
BACKGROUND: The energy density of a nutrient drink is one of the main factors that affect the gastric emptying of the solution, while osmolality and viscosity are thought to have only a minimal influence.
METHOD: The rate of gastric emptying of two isoenergetic carbohydrate solutions with different osmolality and viscosity was determined using a double sampling gastric aspiration technique. Six healthy male subjects were studied on two occasions using approximately 550 ml of a solution containing 13.5% of carbohydrate either in the form of a mixture of monomeric glucose and short chain glucose oligomers (G-drink) or of long chain glucose polymers composed of 78% amylopectin and 22% amylose (C-drink).
RESULT: The half emptying time (t(1/2), median and range) for the viscous, markedly hypotonic (62 mosmol/kg) C-drink was faster (17.0 (6.2-31.4) min) than for the moderately hypertonic (336 mosmol/kg) G-drink (32.6 (25.2-40.7) min). The amount (median and range) of carbohydrate delivered to the small intestine was greater during the first 10 min after ingestion of C-drink
(31.8 (15.8-55.9) g) than after ingestion of G-drink (14.3 (6.8-22.2) g). However, there was no difference in the blood glucose (P = 0.73) or serum insulin (P = 0.38) concentration at any time point after ingestion of the two test drinks.
CONCLUSION: The results of this study show that the carbohydrate present in C-drink, although it has the propensity to form a gel, empties from the stomach faster than that of an isoenergetic carbohydrate solution (G-drink) without potentiating increased circulating blood glucose or insulin levels.
REFERENCE: Improved gastric emptying rate in humans of a unique glucose polymer with gel-forming properties. Leiper JB, Aulin KP, Soderlund K. Sc and J Gastroenterol 2000 Nov;35(11):1143-9.
GASTRIC EMPTYING RATE FAVORS MALTODEXTRINS OVER GLUCOSE
The high prevalence of gastrointestinal complaints in long-distance runners makes the movements specific to this type of exercise suspected of causing a disruption of normal gastrointestinal function. Gastric emptying rate is one indicator thereof. In the present study trained volunteers performed similar repeated fluid ingestion tests while running and while bicycling for 80 min at 70% VO2max. Control tests at rest were also conducted. Two drinks containing carbohydrate were tested, one hypertonic, and one isotonic. Artificially sweetened water was used as a control.
Gastric emptying rate of the isotonic drink, expressed as a percentage of the volume in the stomach at the beginning of each measurement period, did not differ between cycling and running during the first 40 min and was faster during cycling than during running between 40 and 80 min. With the hypertonic drink no differences between cycling and running were observed. In comparing gastric emptying rates after each sequential bolus, at rest, the isotonic drink was observed to maintain a high emptying rate, equal to that of water, whereas the hypertonic drink emptied more slowly after the first 20-min period. A similar pattern was observed during both running and cycling. The isotonic drink continued to empty quickly after the initial 20 min, whereas GE rate of the hypertonic drink decreased after the initial 20 min.
REFERENCE: Effects of exercise and carbohydrate composition on gastric emptying. Neufer PD, Costill DL, Fink WJ, Kirwan JP, Fielding RA, Flynn MG, Med Sci Sports Exerc 1986 Dec 18:6 658-62.
CALORIE ABSORPTION RATE IS SUPERIOR USING MALTODEXTRINS
In four mini pigs a segment of the proximal jejunum was temporarily isolated and perfused with two enteral diets containing isocaloric amounts either of glucose or maltodextrin. With regard to total energy, the diets were composed of 60% carbohydrate, 20% protein and 20% fat. The perfusion rates were 60, 120, 240, 360, and 480 kcal/hour. Absorption of glucose and fat from the maltodextrin diet was significantly greater than from the glucose diet, whereas absorption of protein was only slightly enhanced. A net water absorption occurred at perfusion of the isotonic solution with maltodextrin. Perfusing the hypertonic glucose diet, water was secreted. Therefore the flow rate increased from oligomer to monomer glucose source. With enhanced flow rate sodium secretion increased. However, the sodium concentration of the effluent was determined more by the transepithelial water movement than by the sodium secretion. The present results indicate that in enteral diets with interactions among different nutrients there is a 'kinetic advantage' in glucose absorption from maltodextrin compared to glucose. However, the reduced flow rate of the maltodextrin diet due to the lower osmolality contributed to the enhanced absorption.
REFERENCE: Glucose and maltodextrin in enteral diets have different effects on jejunal absorption of nutrients, sodium and water and on flow rate in mini pigs. Weber E, Ehrlein HJ, DTW Dtsch Tierarztl Wochenschr 1998 Dec 105:12 446-9.
BODY FLUID OSMOLALITY CALORIC VALUES
OF SUGAR AND LONG CHAIN CARBOHYDRATES
Gastric Transit Rates Favor Maltodextrin During Exercise
TYPE OF FUEL CALORIES PROVIDED AT
280-303 mOsm. OSMOLALITY
Glucose 0.2 cal/ml
Fructose 0.2 cal/ml
Sucrose 0.4 cal/ml
MALTODEXTRINS 1.0+ cal/ml
WHEN GLUCOSE CONCENTRATIONS EXCEED 6% GASTRIC STRESS OCCURS [GLUCOSE POLYMERS ABSORBED AT 18%]
This study compared the effects of ingesting 6% (MC) and 12% (HC) glucose/electrolyte beverages, and a flavored water placebo (P) on markers of fluid absorption, palatability, and physiological function during prolonged intermittent cycling in the heat. On three occasions, 15 trained male cyclists performed two 60 min cycling bouts at 65% VO2max (E1 and E2). A brief exhaustive performance ride (approximately 3 min) was completed after E1 and E2, and after 20 min recovery (P1, P2, P3). Every 20 min, subjects consumed 275 mL of P, MC or HC. The first drink contained 20 mL of D2O, a tracer of fluid entry into blood plasma. Plasma D2O accumulation was slower for HC than for P and MC (P less than 0.001). HC caused more nausea
(P less than 0.01) and fullness (P less than 0.05) than MC or P, and subjects said they would be less likely to consume HC during training or competition (P less than 0.10). Sweat rates, HR, Tre, Tsk, VO2, and PV were similar for all drinks. Performance of P1, P2, P3 were not different among drinks. However, four cyclists failed to maintain the prescribed work rate during E2 for HC but only one failed for MC and P. These data suggest that the slow absorption of a 12% glucose/electrolyte beverage during prolonged intermittent exercise in the heat may increase the risk of gastrointestinal distress and thereby limit performance.
REFERENCE: Effects of ingesting 6% and 12% glucose/electrolyte beverages during prolonged intermittent cycling in the heat. Davis JM, Burgess WA, Slentz CA, Bartoli WP, Pate RR., Eur J Appl Physiol Occup Physiol 1988;57(5):563-9 [Exercise Biochemistry Laboratory, College of Health, University of South Carolina, Columbia 29208.]
GLUCOSE CAUSES GREATER DROP IN BLOOD SUGAR
The effects of preexercise hyperinsulinemia on exercising plasma glucose, plasma insulin, and metabolic responses were assessed during 50 min cycling at 62% VO2max. Subjects were fed a 6% sucrose/glucose solution (LCHO) or a 20% maltodextrin/glucose solution (HCHO) to induce changes in plasma insulin. During exercise, subjects assessed perceived nauseousness and light-headedness. By the start of exercise, plasma glucose and plasma insulin had increased. In the LCHO trial, plasma glucose values significantly decreased BELOW the baseline value at 30 min of exercise. However, by 40 min, exercise plasma glucose and insulin values were similar to the baseline value. Exercise plasma glucose and insulin did NOT differ from baseline values in the HCHO trial. Ingestion of LCHO or HCHO was not associated with nausea or lightheadedness. It was concluded that the hyperinsulinemia induced by pre-exercise feedings of CHO did NOT result in frank hypoglycemia or adversely affect sensory or physiological responses during 50 min of moderate-intensity cycling.
REFERENCE: Glycemic and insulinemic response to preexercise carbohydrate feedings.
Seifert JG, Paul GL, Eddy DE, Murray R, Int J Sport Nutr 1994 Mar 4:1 46-53.
GLYCOGEN ABSORPTION RATE ENHANCED
BY LONGER CHAIN MALTODEXTRINS CARBS
Glycogen deposition in liver and muscle is significantly greater in rats fed a diet containing barley malt extract than in those fed diets containing glucose or starch. We investigated whether particular components of malt extract (glucose oligomers, inorganic salts, protein) were responsible for this effect. Food-deprived rats were fed diets containing carbohydrates of different chain lengths [glucose, maltose, maltodextrins or malt carbohydrates (84-86 g/100 g)] in the presence and absence of inorganic salts (2 g/100 g) and maltodextrin diets(78 g/100 g) containing either no protein or 20 g casein/100 g. Dietary glucose oligomers caused higher blood glucose concentrations than consumption of glucose or maltose but had no significant influence on liver or muscle glycogen. Salt addition resulted in higher muscle glycogen concentrations but had no effect on blood glucose or liver glycogen. Hepatic glycogen concentrations were significantly greater in rats fed casein compared with those fed no protein. Consumption of malt extract has the following advantages over consumption of diets containing glucose or maltose: 1-better glucose absorption related to the presence of glucose oligomers, 2-greater hepatic glycogen concentrations associated with the protein in malt extract, and 3-greater glycogen concentrations in muscle due to the presence of inorganic salts.
REFERENCE: Dietary components of malt extract such as maltodextrins, proteins and inorganic salts have distinct effects on glucose uptake and glycogen concentrations in rats. Flückiger-Isler R, Mörikofer-Zwez S, Kahn JM, Walter P, J Nutr 1994 Sep 124:9 1647-53.
The mechanisms favoring an isotonic solution of 15-18% glucose polymers/maltodextrins enhanced with electrolytes—so as to prevent negative hypertonic solution influence—appear obvious from the literature reviewed. Since it has been observed that simple sugar solutions elevate osmolar pressures above body fluid levels [280-303 mOsm] significantly, their inefficient absorption rate occurs in endurance events where an athlete consumes too much volume or concentrated (> 8%) simple-sugared solution in order to resolve thirst, fatigue, or electrolyte depletion. While the same negative events may potentially occur when too much glucose polymer [complex carbohydrate] solution is ingested, it appears less likely simply due to the favorable isotonic properties of long chain carbohydrates, which again are absorbed immediately in solution concentrations of 15-18%.