Efficiency of utilization of wheat and milk protein in healthy adults and apparent lysine requirements determined by a single-meal [1-13C]leucine balance protocol.

Background: We recently reported better wheat-protein utilization and a higher apparent lysine requirement than would be predicted, because of adaptive mechanisms of lysine conservation. However, such findings may be subject to the feeding protocol of frequent small meals.

Objective: We used a [1-13C]leucine balance, large single-meal protocol to estimate the utilization of wheat and the consequent lysine requirements.

Human adult amino acid requirements: [1-13C]leucine balance evaluation of the efficiency of utilization and apparent requirements for wheat protein and lysine compared with those for milk protein in healthy adults.

Background: There is considerable debate about the human lysine requirement and the consequent nutritional value of wheat protein.

Objective: We used a novel [1-(13)C]leucine balance protocol to examine whether adaptive mechanisms to conserve lysine allow wheat to be utilized more efficiently than expected according to current estimates of lysine requirements and wheat utilization.

Design: Wheat and milk proteins were compared in 6 adults infused for 9 h with L-[1-(13)C]leucine in the postabsorptive state (0-3 h), who were fed half-hourly with low-protein (2% of energy, 3-6 h) and isoenergetic higher-protein (12-13% of energy, 6-9 h) meals providing maintenance energy intakes.

Variation in the apparent sensitivity of the insulin-mediated inhibition of proteolysis to amino acid supply determines the efficiency of protein utilization.

1. The variability between normal individuals in the efficiency of postprandial protein utilization (PPU), a determinant of the apparent protein requirement, was examined in relation to the relative responses of protein synthesis and proteolysis to protein feeding by means of [1-13C]leucine turnover and balance studies.2.

Aging, protein requirements, and protein turnover.

Current protein requirements for the elderly derive from 1985 FAO/WHO/UNU recommendations of no change with age in adults: i.e., 0.

Protein requirements and ageing: metabolic demand and efficiency of utilization.

The protein requirements of the elderly were investigated with [13C]leucine balance studies of metabolic demand, the efficiency of postprandial protein utilization (PPU) and the consequent apparent protein requirement. Ten elderly subjects aged 68-91 years (five men and five women) and ten young adult subjects aged 21-31 years (five men and five women) were infused with L-[1-13C]leucine for 9 h commencing in the postabsorptive state (0-3 h), continuing during the half-hourly feeding of low-protein meals (LP; protein 3% energy, 3-6 h), and during similar feeding of isoenergetic higher protein meals (HP; protein 15% energy, 6-9 h). Leucine oxidation and balance were determined from plasma [1-13C]-alpha-ketoisocaproate enrichment and expired 13CO2 excretion measured during the 3rd hour of each 3 h period.