Effect of cold exposure on fuel utilization in humans: plasma glucose, muscle glycogen, and lipids.
The relative roles of circulatory glucose, muscle glycogen, and lipids in shivering thermogenesis are unclear. Using a combination of indirect calorimetry and stable isotope methodology ([U-13C]glucose ingestion), we have quantified the oxidation rates of these substrates in men acutely exposed to cold for 2 h (liquid conditioned suit perfused with 10 degrees C water). Cold exposure stimulated heat production by 2.6-fold and increased the oxidation of plasma glucose from 39.4 +/- 2.4 to 93.9 +/- 5.5 mg/min (+138%), of muscle glycogen from 126.6 +/- 7.8 to 264.2 +/- 36.9 mg glucosyl units/min (+109%), and of lipids from 46.9 +/- 3.2 to 176.5 +/- 17.3 mg/min (+376%). Despite the observed increase in plasma glucose oxidation, this fuel only supplied 10% of the energy for heat generation. The major source of carbohydrate was muscle glycogen (75% of all glucose oxidized), and lipids produced as much heat as all other fuels combined. During prolonged, low-intensity shivering, we conclude that total heat production is unequally shared among lipids (50%), muscle glycogen (30%), plasma glucose (10%), and proteins (10%). Therefore, future research should focus on lipids and muscle glycogen that provide most of the energy for heat production.
Haman
François
F
Département de Biologie, Canada G9A 5H7.
Péronnet
François
F
Kenny
Glen P
GP
Massicotte
Denis
D
Lavoie
Carole
C
Scott
Chris
C
Weber
Jean-Michel
JM
D000328:Adult; D000465:Algorithms; D019540:Area Under Curve; D001786:Blood Glucose / Q000378:metabolism*; D001831:Body Temperature / Q000502:physiology; D001833:Body Temperature Regulation / Q000502:physiology; D002153:Calorimetry, Indirect; D003080:Cold Temperature; D005230:Fatty Acids, Nonesterified / Q000097:blood; D006003:Glycogen / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000097:blood; D019344:Lactic Acid / Q000097:blood; D050356:Lipid Metabolism; D015227:Lipid Peroxidation; D008297:Male; D008660:Metabolism / Q000502:physiology*; D018482:Muscle, Skeletal / Q000378:metabolism*; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000502:physiology
D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D019344:Lactic Acid; D006003:Glycogen