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Effects of carbohydrate availability on sustained shivering I. Oxidation of plasma glucose, muscle glycogen, and proteins

¹Biology Department and ³School of Human Kinetics, University of Ottawa, Ottawa, Ontario K1N 6N5; ²Département de Kinésiologie, Université de Montréal, Québec H3C 3S7; ⁴Département de Kinanthropologie, Université du Québec à Montréal, Montréal, Québec H3C 3P8; and ⁵Département des Sciences de l'Activité Physique, Université du Québec à Trois-Rivières, Trois-Rivières, Québec, Canada G9A 5H7

Submitted 29 April 2003 ; accepted in final form 26 August 2003

Carbohydrates (CHO) can play an important thermogenic role during shivering, but the effect of their availability on the use of other oxidative fuels is unclear. Using indirect calorimetry and tracer methods ([U-¹³C]glucose ingestion), we have determined the specific contributions of plasma glucose, muscle glycogen, proteins, and lipids to total heat production (_prod) in men exposed to cold for 2-h (liquid-conditioned suit perfused with 10°C water). Measurements were made after low-CHO diet and exercise (Lo) and high-CHO diet without exercise (Hi). The size of CHO reserves had no effect on _prod but a major impact on fuel selection before and during shivering. In the cold, a complete shift from lipid oxidation for Lo (53, 28, and 19% _prod for lipids, CHO, and proteins, respectively) to CHO-based metabolism for Hi (23, 65, and 12% _prod for lipids, CHO, and proteins, respectively) was observed. Plasma glucose oxidation remains a minor fuel under all conditions (<13% _prod), falling to 7% _prod for Lo. Therefore, adjusting plasma glucose oxidation to compensate for changes in muscle glycogen oxidation is not a strategy used for maintaining heat production. Instead, proteins and lipids share responsibility for this compensation. We conclude that humans can show remarkable flexibility in oxidative fuel selection to ensure that heat production is not compromised during sustained cold exposure.

energy metabolism; shivering thermogenesis; heat loss; plasma glucose oxidation; stable isotopes; glycogen reserves

This article has been cited by other articles:

				F. Haman, C. G. Scott, and G. P. Kenny Fueling shivering thermogenesis during passive hypothermic recovery J Appl Physiol, October 1, 2007; 103(4): 1346 - 1351. [Abstract] [Full Text] [PDF]

				F. Haman Shivering in the cold: from mechanisms of fuel selection to survival J Appl Physiol, May 1, 2006; 100(5): 1702 - 1708. [Abstract] [Full Text] [PDF]

				F. Haman, F. Peronnet, G. P Kenny, D. Massicotte, C. Lavoie, and J.-M. Weber Partitioning oxidative fuels during cold exposure in humans: muscle glycogen becomes dominant as shivering intensifies J. Physiol., July 1, 2005; 566(1): 247 - 256. [Abstract] [Full Text] [PDF]

				F. Haman, S. R. Legault, and J.-M. Weber Fuel selection during intense shivering in humans: EMG pattern reflects carbohydrate oxidation J. Physiol., April 1, 2004; 556(1): 305 - 313. [Abstract] [Full Text] [PDF]

				F. Haman, S. R. Legault, M. Rakobowchuk, M. B. Ducharme, and J.-M. Weber Effects of carbohydrate availability on sustained shivering II. Relating muscle recruitment to fuel selection J Appl Physiol, January 1, 2004; 96(1): 41 - 49. [Abstract] [Full Text] [PDF]