Higher weight at birth is related to decreased maternal amino acid oxidation during pregnancy

Background: Small size at birth is associated with cardiovascular disease in adult life. Decreased fetal growth may result from a limitation in the nutrient supply to the fetus. Net tissue deposition in the mother and fetus increases the demand for nitrogen, but because maternal consumption of protein does not increase, there must be a change in the partitioning of amino acids, away from oxidation and toward deposition.Objective: Our objective was to characterize amino acid oxidation in pregnancy and to investigate whether the relative partitioning of amino acids was related to fetal growth.Design: We determined amino acid oxidation as urea production in 25 women during mid (17–19 wk) and late (26–29 wk) gestation. Urea production was measured from urinary [15N-15N]urea excretion over 48 h after a single oral dose of [15N-15N]urea. We measured the infant’s size at birth.Results: For the group as a whole, urea excretion decreased and amino acid oxidation remained similar between mid and late pregnancy, but there was wide variation between the women. Heavier infants were born to the mothers in whom amino acid oxidation decreased the most during pregnancy (slope of regression line: -80 g · g N-1 · d-1; 95% CI: -129, -31; P = 0.003). After adjustment for length of gestation and the infant’s sex, the change in maternal amino acid oxidation explained 34% of the variation in birth weight.Conclusions: Amino acid oxidation varied widely between the women during pregnancy. Understanding the ability of a pregnant woman to adapt metabolically may have implications for establishing dietary recommendations in pregnancy

Relationship of maternal protein turnover and lean body mass during pregnancy and birth length

Epidemiological evidence shows that small size at birth is associated with an increased risk of developing cardiovascular and metabolic disease in adult life. We have examined the relationships between size at birth and maternal body composition and protein turnover in normal pregnant women. A group of 27 multiparous Caucasian women with singleton pregnancies were studied at around 18 and 28 weeks' gestation. Body composition was determined by anthropometry, and whole-body protein turnover was estimated by using a single oral dose of [15N]glycine and the end-product method. The baby's weight and length were measured within 48 h of birth. Mothers with a greater lean body mass had higher rates of protein turnover at 18 weeks' gestation. This association was largely accounted for by differences in the mother's visceral, rather than muscle, mass. Mothers who had higher protein turnover at 18 weeks' gestation had babies that were longer at birth. After adjustment for the duration of gestation and the baby's sex, 26% of the variation in length at birth was accounted for by maternal protein synthesis at 18 weeks' gestation. Maternal protein intake was not associated with the baby's birth length. Thus the mother's ability to nourish her fetus is influenced by her body composition and her rate of protein turnover. Dietary intake does not adequately characterize this ability

Cut-off points for anthropometric indices of adiposity: differential classification in a large population of young women

Anthropometric indices of adiposity include BMI, waist circumference and waist:height ratio. In the recruitment phase of a prospective cohort study carried out between 1998 and 2002 we studied a population sample of 11 786 white Caucasian non-pregnant women in Southampton, UK aged 20-34 years, and explored the extent to which proposed cut-off points for the three indices identified the same or different women and how these indices related to adiposity. Height, weight and waist circumference were measured and fat mass was estimated from skinfold thicknesses; fat mass index was calculated as fat mass/height1.65. Of the subjects, 4869 (42 %) women were overweight (BMI >/= 25 kg/m2) and 1849 (16 %) were obese (BMI >/= 30 kg/m2). A total of 890 (8 %) subjects were not overweight but had a waist circumference >/= 80 cm and 748 (6 %) subjects were overweight but had a waist circumference /= 0.5. Of the variation in fat mass index, 85 % was explained by BMI, 76 % by waist circumference and 75 % by waist:height ratio. Our findings demonstrate that many women are differentially classified depending on which index of adiposity is used. As each index captures different aspects of size in terms of adiposity, there is the need to determine how the three indices relate to function and how they can be of use in defining risk of ill health in women

Birth weight, weight at 1 y of age, and body composition in older men: findings from the Hertfordshire Cohort Study

Background: Size in early life is related to adult body mass index, and early environmental influences have been proposed to have lifelong consequences for obesity. However, body mass index also reflects fat-free mass, and few studies have examined the relation between size in early life and direct measures of body composition in older people. Objective: We investigated the associations of birth weight and weight at 1 y of age with body composition in older men. Design: We carried out a retrospective cohort study in Hertfordshire, United Kingdom. Men who were born between 1931 and 1939 and for whom there were records of birth weight and weight at 1 y of age (n = 737) participated in the study. The main outcome measures were adult body mass index, fat-free mass, and fat mass. Results: Birth weight was significantly and consistently positively associated with adult body mass index and fat-free mass but not with measures of adult fat mass. In contrast, weight at 1 y of age was associated with adult body mass index, fat-free mass, and fat mass. Conclusions: The consistently reported positive relation between birth weight and adult body mass index may reflect prenatal and maternal influences on fat-free mass rather than on fat mass in older people. The postnatal environment may be more influential than prenatal factors in the development of obesity in later life