Protein Requirements of Healthy Pregnant Women during Early and Late Gestation Are Higher than Current Recommendations

Background: Adequate maternal dietary protein intake is necessary for healthy pregnancy. However, current protein intake recommendations for healthy pregnant women are based on factorial calculations of nitrogen balance data derived from nonpregnant adults. Thus, an estimate of protein requirements based on pregnancy-specific data is needed. Objective: The objective of this study was to determine protein requirements of healthy pregnant women at 11-20 (early) and 31-38 (late) wk of gestation through use of the indicator amino acid oxidation method. Methods: Twenty-nine healthy women (24-37 y) each randomly received a different test protein intake (range: 0.22-2.56g.kg(-1) .d(-1)) during each study day in early (n = 35 observations in 17 women) and late (n = 43 observations in 19 women) gestation; 7 women participated in both early and late gestation studies. The diets were isocaloric and provided energy at 1.7 x resting energy expenditure. Protein was given as a crystalline amino acid mixture based on egg protein composition, except phenylalanine and tyrosine, which were maintained constant across intakes. Protein requirements were determined by measuring the oxidation rate of L[1-C-13]phenylalanine to (CO2)-C-13 ((FCO2)-C-13). Breath and urine samples were collected at baseline and isotopic steady state. Linear regression crossover analysis identified a breakpoint (requirement) at minimal (FCO2)-C-13 in response to different protein intakes. Results: The estimated average requirement (EAR) for protein in early and late gestation was determined to be 1.22 (R-2 = 0.60; 95% Cl: 0.79, 1.66 g . kg(-1) .d(-1)) and 1.52 g . kg(-1) . d(-1) (R-2 = 0.63; 95% Cl: 1.28, 1.77 g . kg(-1) . d(-1)), respectively. Conclusions: These estimates are considerably higher than the EAR of 0.88g. kg(-1).d(-1) currently recommended by the Dietary Reference Intakes. To our knowledge, this study is the first to directly estimate gestational stage specific protein requirements in healthy pregnant women and suggests that current recommendations based on factorial calculations underestimate requirements.