Nutrition During Pregnancy Part I: Weight Gain, Part II: Nutrient Supplements (1990) / Chapter Skim
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19 Protein and Amino Acids
19 Protein and Amino Acids
Pages 380-389
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From page 380... ...
Thus, net requirements for nonessential amino acids can be met both by dietary protein and by endogenous synthesis of amino acids. Ordinarily, the following amino acids are considered to be essential amino acids, because they cannot be synthesized by mammals: histidine, isoleucine, leucine, lysine, methionine + cystine, phenylalanine + tyrosine, threonine, tryptophan, and valine (N RC, 1989~.
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From page 381... ...
Developmental immaturity of biochemical pathways may also limit conversion of pairs of metabolically related essential amino acids, such as conversion of phenylalanine to tyrosine. In postnatal life, ingested protein is hydrolyzed to amino acids, which are absorbed and carried via the portal system to the liver.
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From page 382... ...
Because of the complexity of the transport processes and placental metabolism, it is difficult to predict the effect of altered maternal protein intake on fetal amino acid metabolism, both in terms of the total quantitative amino acid flux and in terms of relative changes in the fluxes of individual amino acids. The fetus must handle rapid entry of both exogenous and endogenous amino acids, and it must provide for the rapid accretion of new protein (Battaglia, 1986~.
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From page 383... ...
Some investigators have expressed technical concerns about using turnover measurements to estimate protein requirements during pregnancy (Fitch and King, 1987~. All human studies to date have used nonessential amino acids to measure the turnover of protein in pregnant women, further complicating the interpretation of these data.
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From page 384... ...
USUAL INTAKES As discussed in Chapter 13, usual protein intakes by pregnant women in the United States range from 75 to 110 g/day. The estimated average intakes of protein by low-income women enrolled in the Supplemental Food Program for Women, Infants, and Children (WIC)
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From page 385... ...
Studies in the developed world have also demonstrated minimal changes in birth weight as a result of protein supplementation. In the United Kingdom, protein-energy supplementation of pregnant Asian women in Birmingham led to significantly higher maternal weight gains than did energy supplements alone; however, only the supplement that contained vitamins in addition to protein and energy was associated with a significant increase in birth weight (Viegas et al, 1982a,b)
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From page 386... ...
~ summarize, in many studies, protein-energy supplements have been given to pregnant women in an effort to determine the effect on maternal and fetal outcomes. In many of them, no significant changes were found in either birth weight or gestational duration; in others, small changes from a 30- to 100-g increase in birth weight were observed.
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From page 387... ...
1988. Umbilical amino acid concentrations in appropriate and small for gestational age infants: a biochemical difference present in utero.
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From page 388... ...
1981. The Bacon Chow study: maternal nutritional supplementation and birth weight of offspring.
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From page 389... ...
1982b. Dietary protein energy supplementation of pregnant Asian mothers at Sorrento, Birmingham.
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