Carbohydrate and fat may vary in their ability to support protein accretion and growth. If so, variations in the source of nonprotein energy might be used to therapeutic advantage in enterally fed low-birth-weight infants. To test the hypothesis that high-carbohydrate diets are more effective than isocaloric highfat diets in promoting growth and protein accretion, low-birthweight infants weighing 750 -1600 g at birth were randomized in a double blind study to receive one of five formulas differing only in the quantity and quality of nonprotein energy. Groups 1, 2, and control received 130 kcal·kg -1 ·d -1 with 35, 65, and 50% of the nonprotein energy as carbohydrate. Groups 3 and 4 received energy intake of 155 kcal·kg -1 ·d -1 with 35 and 65% of the nonprotein energy as carbohydrate. Protein intake of all groups was 4 g·kg -1 ·d -1 . Growth and metabolic responses were followed weekly, and macronutrient balances including 6-h indirect calorimetry were performed biweekly. Greater rates of weight gain and nitrogen retention were observed at high-carbohydrate intake compared with high-fat intake at both gross energy intakes. Greater rates of energy storage and an increase in skinfold thickness were observed in group 4 (high-energy highcarbohydrate diet) despite higher rates of energy expenditure. These data support the hypothesis that at isocaloric intakes, carbohydrate is more effective than fat in enhancing growth and protein accretion in enterally fed low-birth-weight infants. However, a diet with high-energy and high-carbohydrate content also results in increased fat deposition. The American Academy of Pediatrics has suggested that a logical goal for nutritional support of the preterm LBW infant is to achieve postnatal growth approximating that of a normal fetus of the same postconceptional age (1, 2). Attempts to achieve this goal by feeding enriched diets have been successful in supporting the intrauterine rate of weight gain (3-7), but invariably these diets lead to a disproportionate increase in body fat. The reasons for this postnatal failure to maintain the high fetal rates of protein accretion relative to fat deposition are unknown. One difference between fetal and neonatal life is the relatively greater dependence of the fetus on carbohydrate versus fat as an energy source. If the fetus is relatively more dependent on carbohydrate than fat, then it is possible that the same is true of the fetus ex utero, i.e. the preterm LBW infant. This reintroduces a question of long-standing concern in developmental nutrition, namely, do carbohydrate and fat differ in some fundamental way in their ability to support protein synthesis? Indeed, there is experimental evidence that supports the hypothesis that calorie for calorie, utilization of carbohydrate as an energy source is more effective than fat in supporting protein accretion (8 -11); other research, however, asserts that this effect is transient (12). In enterally fed LBW infants, this hypothesis remains untested.LBW infants are ideal subjects for studying th...

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IntroductionCare takers have long noted that low birth weight (LBW) infants seem more comfortable when cared for in the prone position. They also spend more time in quiet sleep (1-3) and often have improvements in ventilation (4) as compared to supine position. These perceptions attracted further interest with the recognition that sudden infant death syndrome (SIDS) was related to prone body positioning during sleep [5][6][7][8][9][10] and decreased with the introduction of public health measures designed to reduce the incidence of prone sleeping [11]. The very fact that supine position protects against SIDS is counterintuitive, but nonetheless true. Numerous physiological differences related to body position have been reported [1][2][3][4][12][13][14][15][16][17][18][19][20][21][22][23] and reviewed [24], and several hypotheses have been formulated to explain how these differences might render infants more vulnerable to SIDS. One prominent hypothesis relates SIDS to relative increases in body temperature [25][26][27][28][29][30][31][32][33][34], thought to be caused by less efficient heat dissipation in the prone position.Evidence consistent with this hypothesis includes the observation that the victims of SIDS are commonly found in unusually warm environments, often feel warm and/or diaphoretic when discovered, and exhibit higher than expected rectal temperatures at examination or autopsy [32,33]. In addition, SIDS victims have often been wrapped tightly in clothing/bedding and/ or a history of a recent febrile illness is often elicited [34].A detailed study of the interactions among body position, sleep states, heat production, surface temperature profiles and surface temperature gradients, and cardiorespiratory activity in LBW infants may provide important information concerning physiological disturbances that predispose to SIDS, a condition to which LBW infants are especially susceptible as they grow to infancy [6]. The primary objective of this study was to test the hypothesis that despite lower metabolic rate (heat production), prone body position during sleep is associated with systematic Send correspondence to: Rakesh Sahni, M.D. Department of Pediatrics, College of Physicians and Surgeons, Columbia University, 630 W. 168th Street, New York, NY 10032, Tel. (212) 305-8500, Fax: (212) 305-8796, E-mail: E-mail: rs62@columbia.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Author ManuscriptEarly Hum Dev. Author manuscript; available in PMC 2010 August 1. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript increases in ab...