Abstract
To provide insight into the cause of metabolic acidosis (MA) observed in LBW infants fed high casein formulas, net acid balances (NAB) were preformed in infants (BW 900-1750g) fed formulas with a whey:casein ratio of either 18:82 (A; n=8) or 60:40 (B; n=8). Both provided 3.4g/kg.d of protein and 120 kcal/kg.d. Simultaneously, plasma and urinary amino acid (AA) concentrations including both bound and free cysteine concentrations (Malloy, et al, Anal. Biochem.112:407, 1981) were determined.
Neither growth nor nitrogen retention of the 2 groups differed. No infant in A or B developed MA and NAB did not differ (A=-1.61 mEq/kg.d; B=-1.72 mEq/kg.d). However, urinary organic acid excretion (OA), a component of net acid intake (NAI), was greater in A(1.81±0.3 mEq/kg.d vs 1.45±0.12 mEq/kg.d; p<0.05). Plasma {Tyr} but not other {AA} was higher in A(28.6±18.9 μm/d7 vs 11.5±2.7 μm/d7; p<0.05) suggesting that some of their greater OA was a tyr metabolite. Neither other NAI components nor net acid output components differed. Despite the difference in cys intake, neither plasma nor urinary bound or free {cys} differed. Urinary {tau} of B was higher (5.27±0.5 μm/kg.d vs 4.17±0.7 μm/kg.d; p<0.05) but only 1/5 that of infants fed human milk (Rassin, et al, Pediatr. 71:179, 1983).
These data provide new information concerning both the mechanism of MA that may occur in infants fed higher intakes of casein and the importance of cys intake. They do not provide strong support for the superiority of whey proteins when total protein intake is <3.4g/kg.d.
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Kashyap, S., Okamoto, E., Kanaya, S. et al. IMPORTANCE OF PROTEIN QUALITY IN FEEDING THE LOW BIRTH WEIGHT (LBW) INFANT. Pediatr Res 18 (Suppl 4), 201 (1984). https://doi.org/10.1203/00006450-198404001-00646
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DOI: https://doi.org/10.1203/00006450-198404001-00646