Urea and plasma protein differ in natural 15N abundance up to 10%. The origin of this difference is the branched nitrogen metabolism in the liver. One main branch is the protein synthesis pathway, the other the urea synthesis pathway. By this branching 15N of precursor amino acids is depleted in urea while it is enriched in protein. With the 15N abundance of precursor amino acids, which may be taken from jejunum tissue, utilization of amino acids in liver metabolism can be calculated from isotope discrimination in either pathway. This was investigated by feeding different proteins to rats. When feeding high quality protein (whey protein) utilization of amino acids in liver metabolism at requirement intake was better than at zero protein intake (> 85% vs. 70%). From this we conclude that the pattern of amino acids available from the metabolic pool at zero protein intake is characterized by an imbalance. This endogenous imbalance can be complemented by exogenous dietary amino acids so that nitrogen excretion may even be smaller than the so-called "obligatory" losses of intakes not exceeding requirement. Thus, the quality of dietary protein is reflected not only by N balance. It also may be quantified by analysis of isotope discrimination in nitrogen metabolism of the liver. In addition, the quality of amino acid pattern available from the metabolic pool is indicated by this method.

The aim of the current study was to assess phase angle (PA) and bioelectrical impedance vectors (BIVA) in adolescent (n = 105, 12-19 y) and adult (n = 90, 20-50 y) male athletes practicing varied sports modalities. Bioelectrical impedance analysis (BIA) was performed with a single-frequency tetrapolar impedance analyzer after the athletes had fasted overnight for 8 h. PA and BIVA were determined from BIA data. PA presented correlations (P < .01) with body-mass index (r = .58) in all athletes and also with age in adolescent (r = .63) and adult (r = -.27) athletes. Compared with adults, adolescent athletes presented lower PA and higher frequency of PA below the 5th percentile of a reference population (P < .001). The adolescents with low PA were mostly football and basketball players. The BIVA confidence ellipses of adult and adolescent athletes were different (P < .001) between them and from their respective reference populations and were closer than those of adult and adolescent nonathletes. About 80% of the athletes were in the 95th percentile of BIVA tolerance ellipses and in quadrants consistent with adequate body cell mass and total body water. The adolescent athletes outside the 95th percentile ellipse were all football and basketball players who showed indications of decreased water retention and body cell mass and of increased water retention, respectively. PA and BIVA ellipses showed that the intense training routine of the athletes changed functional and hydration parameters and that the magnitude of these changes in adolescents may depend on the sport modality practiced.

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The effect of heat treatment of germinated soybean, lupin, and black bean on chemical composition and protein utilization in rats was evaluated. Heat treatment caused complete inactivation of trypsin inhibitors whereas it did not affect phytic acid levels. Proximate components, minerals, and amino acids did not change, but low molecular weight sugars were affected by heat treatment differently for each germinated legume. The sugar digestibility ratio (total digestible sugars/total nondigestible sugars) in germinated black beans doubled after heat treatment. True protein digestibility (TD) increased with heat treatment only in germinated soybean. Net protein utilization was markedly improved (20%) with heat treatment in germinated soybean and lupin. Utilizable protein of heat-treated germinated legumes was 289, 236, and 132 g/kg of legume dry weight for soybean, lupin, and black bean, respectively. Supplementation with methionine did not alter TD but improved all other indices of protein utilization in the germinated legumes, particularly in black bean. All three germinated legumes become equivalent in protein quality when heating and supplementation with methionine are combined with germination. The use of germinated heat-treated soybean, lupin, and black bean on their own and/or as food ingredients is nutritionally advantageous due to the low content of nondigestible oligosaccharides and the high protein utilization.

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The placental transfer of retinol and β-carotene was assessed based on maternal serum, cord serum and placental levels at term parturition in women with adequate (n = 15; serum retinol > 20 μg/dl) and subadequate (n = 16; serum retinol ≤ 20 μg/dl) vitamin-A status. There was no difference in retinol and β-carotene levels in placenta and cord serum between these groups. However, differences in the relation of maternal, placental and cord blood components were observed between women with adequate and subadequate vitamin-A status. In women with subadequate status, circulating fetal retinol levels correlated with placental retinol levels, and maternal serum β-carotene correlated with placental retinol. Within this group, maternal serum β-carotene and cord serum retinol correlated significantly in women with serum retinol levels lower than 15 μg/dl. These results suggest that β-carotene may be a precursor of retinol in placenta and that this conversion may depend on the nutritional status of the mother, being particularly effective in a more depleted state.