Dietary protein, physiological condition and metabolic amino acid utilisation
1993
Weijs, P.J.M.
This thesis describes the investigated effects of the level of dietary protein intake and the physiological condition of the animal on the percental oxidation of leucine. This measure reflects which part of the free leucine pool was used for protein and energy metabolism. The employed technique consisted of a constant infusion of 14C-leucine and simultaneous collection of expired 14CO 2 . The aim of the study was to identify the causes and objectives of amino acid losses and therefore the metabolic basis for their requirements. The percental oxidation of leucine was decreased in the postabsorptive state by chronic protein restriction, growth and pregnancy, and was increased by a period of fasting, meal frequency and exercise. The transition from the postabsorptive to the postprandial state caused an increase in expired 14CO 2 . The percental oxidation in the postprandial state increased with the protein content of the meal. During different phases after the meal the percental oxidation was decreased by growth and pregnancy (2-4 h), chronic protein restriction (4-6 h), and training (6 h) and increased by the period of fasting (6 h). Several other aspects, such as the level of leucine intake, the use of tracer isotopomers, duration of tracer infusion, and the route of tracer administration were investigated. From these studies it was concluded that there is a large diurnal variation in amino acid losses, which have to be accounted for in the estimation of nutritional requirements.
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