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UBC Theses and Dissertations

Determination of protein requirements of healthy pregnant women during early and late gestation using the indicator amino acid oxidation technique Stephens, Trina


Adequate maternal dietary protein (PRO) intake is necessary to support rapid tissue accretion during a healthy pregnancy. Both insufficient and excessive maternal PRO intake during pregnancy is associated with intrauterine growth restriction (IUGR) of the fetus. IUGR increases the risk of neonatal morbidity and mortality, and is associated with an increased risk of future health problems, including cardiovascular disease, kidney disease, obstructive airway disease, and obesity. However, current PRO intake recommendations for healthy pregnant women are based on factorial calculations of nitrogen balance data derived from non-pregnant adults. Thus, an estimate of PRO requirements based on pregnancy-specific data is needed. PRO requirements of healthy pregnant women at 11-20 (early) and 31-38 (late) weeks gestation were determined using the indicator amino acid oxidation (IAAO) method. Twenty-nine healthy women (age 24-37) each randomly received a different test PRO intake (range = 0.22-2.56 g/kg/day) during each study day in early (n=37) and late (n=44) gestation. The diets were isocaloric and provided energy at 1.7 X resting energy expenditure (REE). PRO was given as a crystalline amino acid mixture based on egg PRO composition, except phenylalanine and tyrosine, which were maintained constant across intakes. PRO requirements were determined by measuring the oxidation of L-[1-¹³C]phenylalanine to ¹³CO₂ (F¹³CO₂). Breath and urine samples were collected at baseline and isotopic steady state. Linear regression crossover analysis identified a breakpoint (requirement) at minimal F¹³CO₂ in response to different PRO intakes. The estimated average requirement (EAR) for PRO in early and late gestation was determined to be 1.22 and 1.52 g/kg/d, respectively. Both of these estimates are significantly greater than the EAR of 0.88 g/kg/d currently recommended by the Dietary Reference Intakes (DRI 2005). Our results indicate increased demand for PRO before 20 weeks gestation (on a gram per kilogram body weight basis), a consideration that has not been addressed by current DRI recommendations. This study is the first to directly estimate gestational PRO requirements in a population composed solely of healthy pregnant women, and suggests that current recommendations based on the nitrogen balance method and factorial calculations underestimate PRO requirements.

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