title: High rates of exogenous carbohydrate oxidation from starch ingested during prolonged exercise.
abstract: This study compared the gastric emptying and oxidation of two 15% carbohydrate (CHO) solutions: a 22-chain-length glucose polymer (GP) and soluble starch (SS). Six endurance-trained subjects ingested 1,200 ml of either GP or SS while cycling for 90 min at 70% of maximal oxygen consumption (VO2max). Whereas the calculated total CHO oxidation (GP 266.8 +/- 41.9 g; SS 263.6 +/- 28.9 g) and the volume emptied from the stomach (GP 813 +/- 130 ml; SS 919 +/- 116 ml) were similar, the appearance of the 14C label in plasma occurred more rapidly from ingested SS than from GP (P less than 0.001). This resulted in a significantly greater rate of SS oxidation than that from GP (SS 105.9 +/- 21.9 g, GP 49.6 +/- 10.2 g; P less than 0.001). Exogenous CHO oxidation from GP accounted for 19% of total CHO oxidation, whereas the corresponding value for SS was 40%. This study suggests that the oxidation of SS and GP solutions ingested during exercise at 70% VO2max is not limited by gastric emptying. Rather, it appears to be either the rate of digestion or absorption of these solutions that determines their utilization.
authors.affiliation: Liberty Life Chair of Exercise and Sports Science and Medical Research Council/University of Cape Town, South Africa.
authors.forename: J A
authors.initials: JA
authors.lastname: Hawley
authors.forename: S C
authors.initials: SC
authors.lastname: Dennis
authors.forename: B J
authors.initials: BJ
authors.lastname: Laidler
authors.forename: A N
authors.initials: AN
authors.lastname: Bosch
authors.forename: T D
authors.initials: TD
authors.lastname: Noakes
authors.forename: F
authors.initials: F
authors.lastname: Brouns
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D015444:Exercise / Q000502:physiology*; D005746:Gastric Emptying; D005936:Glucans / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000097:blood; D008297:Male; D009132:Muscles / Q000378:metabolism; D009994:Osmolar Concentration; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D012995:Solubility; D012996:Solutions; D013213:Starch / Q000378:metabolism*
chemical_list: D001786:Blood Glucose; D005936:Glucans; D007328:Insulin; D012996:Solutions; D013213:Starch