PROTEIN QUALITY AND QUANTITY IN PRETERM INFANTS ON THE SAME ENERGY INTAKE

Abstract

Whey predominant formulas cause less metabolic stress in LBW infants but their nutritional benefit as well as that of casein hydrolysate formulas seem limited to a better % nitrogen absorption. Fifteen LBW AGA infants weighing 1.3-1.6 kg were assigned to 3 isocaloric diets differing in the quantity and form of nitrogen delivered. Nitrogen was fed as whole proteins with a whey/casein ratio of 60/40(I), 20/80(II) or as a casein hydrolysate (III) at concentrations of 310, 240 and 314 mg/dl. A balance study was done between 21 and 30 d after birth. Energy intake was the same (150 kcal/kg/d) and the % fat absorption was unaffected by the presence of 40% MCT in I and III. In subjecs fed III, the % nitrogen absorbed (93.5±.8) was greater than in those fed either I (87.2±1.7) or II (87.8±.7). Nitrogen retention as mg/kg/d and as mg/kg/100 kcal metabolizable energy on I (481.6±30.4 and 170.4±8.3) and on III (505.7±34.8 and 179.0± 14.3) did not differ but was greater than on II (399.0±19.2 and 127.7±4.3). Daily weight gain from regained birth weight to 2200 g was the same on I (35.9±2.9) as on III (30.2±3.4) but lower on II (28.6±1.8). Height (cm/wk) and head circumference (cm/wk) monitored over 3 months also showed an advantage of I (1.05±.08 and .81±.04) and III (.90±.04 and .80±.03) over II (.84±.02 and .67±.04). These data suggest that on high energy intakes, protein quality may not affect nitrogen retention and growth unless the quantity of protein ingested falls below a critical level.

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