title: Metabolic adaptation to feeding and fasting during lactation in humans.
abstract: The aim of these studies was to determine the metabolic adaptation to fasting and feeding during lactation. Normal lactating (L) and nonlactating (NL) women (n = 6 each) were studied using infusions of [U-13C]glucose and [2-13C]glycerol during: 1) a 24-h fast, and 2) ingestion of Sustacal (protocol 1). In addition, 8 L and 6 NL women were studied during infusion of [6,6-2H2]glucose and ingestion of a glucose meal containing [1-13C]glucose (protocol 2). Protocol 1: Glucose production rate (GPR) during fasting was 33% higher in the L women (12.5 +/- 1.0 vs. 9.4 +/- 0.5 micromol x kg(-1) x min(-1); P < 0.03). Fractional gluconeogenesis (GNG), GNG rate, glucose, lactate, beta- hydroxybutyrate, FFA, insulin, and C-peptide were similar in both groups during feeding and fasting, but glycogenolysis was 50% higher in fasting L women. Protocol 2: Although GPR was slightly increased in the L group (L, 1.8 +/- 0.2 micromol x kg(-1) x min(-1); NL, 1.2 +/- 0.2 micromol x kg(-1) x min(-1); P < 0.04), no other differences were observed in splanchnic and systemic metabolism of ingested glucose between L and NL women. Insulin concentrations were lower in L women compared with controls (L, 15 +/- 3 microU/ml; NL, 28 +/- 6 microU/ml; P = 0.05). In conclusion, the increased glucose demands of lactation are met by increased GPR as a result of increased glycogenolysis but not GNG or by increased use of FFA. During feeding, lactating women handle oral carbohydrates normally but have increased insulin sensitivity.
authors.affiliation: Department of Pediatrics, Children's Nutrition Research Center, United States Department of Agriculture/Agricultural Research Service, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Stelios
authors.initials: S
authors.lastname: Tigas
authors.forename: Agneta
authors.initials: A
authors.lastname: Sunehag
authors.forename: Morey W
authors.initials: MW
authors.lastname: Haymond
mesh_terms: D020155:3-Hydroxybutyric Acid / Q000097:blood; D000222:Adaptation, Physiological; D000328:Adult; D001786:Blood Glucose / Q000032:analysis; D002096:C-Peptide / Q000097:blood; D002247:Carbon Isotopes; D004435:Eating; D005215:Fasting; D005227:Fatty Acids / Q000097:blood; D005260:Female; D005934:Glucagon / Q000097:blood; D005947:Glucose / Q000008:administration & dosage / Q000378:metabolism; D005990:Glycerol / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000097:blood; D007774:Lactation; D019344:Lactic Acid / Q000096:biosynthesis / Q000097:blood; D008895:Milk, Human / Q000378:metabolism; D049590:Postpartum Period; D013997:Time Factors
chemical_list: D001786:Blood Glucose; D002096:C-Peptide; D002247:Carbon Isotopes; D005227:Fatty Acids; D007328:Insulin; D019344:Lactic Acid; D005934:Glucagon; D005947:Glucose; D005990:Glycerol; D020155:3-Hydroxybutyric Acid