title: Effect of caffeine co-ingested with carbohydrate or fat on metabolism and performance in endurance-trained men.
abstract: We examined the effect of caffeine co-ingested with either carbohydrate or fat on metabolism and performance in eight endurance-trained subjects who performed a random order of four experimental trials consisting of 120 min of steady-state ergometer cycling at 70 % of maximal O(2) uptake (SS) followed by a time trial in which subjects completed a set amount of work (7 kJ kg-1) as quickly as possible. One hour before SS subjects ingested either 2.6 g kg-1 carbohydrate (CHO); 2.6 g kg-1 CHO + 6 mg kg-1 caffeine (CHO + CAF); 1.2 g kg-1 fat with 2000 U I.V. heparin (FAT); or 1.2 g kg-1 fat with 2000 U I.V. heparin + 6 mg kg-1 caffeine (FAT + CAF). The rate of carbohydrate oxidation was higher (micromol kg-1 min-1: CHO, 243 +/- 39 and CHO + CAF, 239 +/- 30 vs. FAT, 196 +/- 48 and FAT + CAF, 191 +/- 55; P < 0.05, values are means +/- S.D.) and the rate of fat oxidation lower (micromol kg-1 min-1: CHO, 19 +/- 8 and CHO + CAF, 22 +/- 7 vs. FAT, 35 +/- 19 and FAT + CAF, 37 +/- 17; P < 0.05) with carbohydrate than fat ingestion. Yet despite lower carbohydrate use with fat feeding, the time taken to complete the time trial was less after carbohydrate than after fat ingestion (min: CHO, 30.37 +/- 7.42 and CHO + CAF, 29.12 +/- 5.62 vs. FAT, 33.02 +/- 8.50 and FAT + CAF, 32.78 +/- 7.70; P < 0.05). We conclude that (1) caffeine co-ingested with either carbohydrate or fat meals has no additive effect on substrate utilization or exercise performance and (2) carbohydrate ingestion before exercise improves subsequent time trial performance compared with fat ingestion. Experimental Physiology (2001) 86.1, 137-144.
authors: Exercise Metabolism Group, Department of Human Biology and Movement Science, RMIT University, Bundoora 3083, Victoria, Australia.
authors: T L
authors: TL
authors: Jacobson
authors: M A
authors: MA
authors: Febbraio
authors: M J
authors: MJ
authors: Arkinstall
authors: J A
authors: JA
authors: Hawley
mesh_terms: D000328:Adult; D001769:Blood / Q000378:metabolism; D002110:Caffeine / Q000494:pharmacology*; D004040:Dietary Carbohydrates / Q000494:pharmacology*; D004041:Dietary Fats / Q000494:pharmacology*; D004734:Energy Metabolism / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D006706:Homeostasis / Q000187:drug effects; D006801:Humans; D008297:Male; D008660:Metabolism / Q000187:drug effects*; D010084:Oxidation-Reduction; D010806:Physical Education and Training; D010807:Physical Endurance; D005082:Physical Exertion / Q000187:drug effects; D013997:Time Factors
chemical_list: D004040:Dietary Carbohydrates; D004041:Dietary Fats; D002110:Caffeine