Submitted to: Journal of Clinical Endocrinology and Metabolism
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/10/2001
Publication Date: 1/1/2002
Citation: Tigas,S., Suhehag,A., Haymond,M.W. 2002. Metabolic adaptation to feeding and fasting during lactation in humans. Journal of Clinical Endocrinology and Metabolism. 87(1):302-307. Interpretive Summary: The increased glucose demands of lactation are met by increased glucose production rate (GPR) as a result of increased glycogenolysis but not by gluconeogenesis or increased use of FFA. During feeding, lactating women handle oral carbohydrates normally but have increased insulin sensitivity. Many women increase their body fat mass with each consecutive pregnancy, because they are unable to lose this fat in the postpartum period regardless of breast-feeding or not. This progressive increase in body fat is associated with increased risks of diabetes mellitus, hypertension and macrovascular disease. By providing insight into some aspects of maternal metabolism during lactation, these data might have great importance in establishing sound dietary guidelines for the lactating woman.
Technical 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.