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UBC Theses and Dissertations

Determination of lysine requirements in healthy pregnant women using the indicator amino acid oxidation technique Payne, Magdalene


Perinatal nutrient status influences the health of both mother and child. Lysine, an essential amino acid found mainly in animal derived products, is the first limiting amino acid in plant proteins. Inadequate lysine intakes during pregnancy may impact foetal health in both the short and long-term. Current Dietary Reference Intakes (DRI) recommendations extrapolate lysine requirements during pregnancy from non-pregnant adult data and may underestimate true requirements. Moreover, these recommendations remain constant throughout pregnancy and do not reflect the dynamic metabolic adaptations that occur during gestation. This study aims to define a quantitative lysine requirement in healthy pregnant women and to determine whether lysine requirements vary between phases of gestation. Two phases of pregnancy (early gestation, 12-19 weeks; late gestation, 33-39 weeks) were studied using the indicator amino acid oxidation (IAAO) technique. Pregnant women (22-36y) consumed a diet containing a random lysine intake (range = 6 - 86 mg/kg/d) in a crystalline amino acid mixture based on egg protein profile. Diets were isonitrogenous with caloric and protein intakes maintained at 1.7 x resting energy expenditure and 1.5g/kg/d, respectively. Breath and urine samples were collected at baseline and isotopic steady state. Lysine requirements were determined by measuring oxidation of L-[1-¹³C]-phenylalanine to ¹³CO₂ (F¹³CO₂). Bi-phase linear regression crossover analysis was used to determine a breakpoint (estimated average requirement, EAR) in F¹³C₂ data. The breakpoint in early gestation (n=27) was determined to be 36.6 mg/kg/d (r² = 0.484, Upper 95% CI = 46.2), similar to current non-pregnant recommendations of 41mg/kg/d. The breakpoint in late gestation (n=36) was determined to be 50.3 mg/kg/d (r² = 0.664, Upper 95% CI = 60.4), and 25% higher than current DRI recommendations of 41 mg/kg/d. Urinary phenylalanine flux did not change in both early and late gestation due to lysine intake. These data are the first to directly define a quantitative requirement for lysine during human pregnancy and to account for gestational age, describing an increase in requirement as pregnancy progresses. We expect these results will have significant implications for setting recommendations globally where plant based diets are the primary source of protein and amino acids.

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