Dose‐response of leucine oxidation with beef feeding in middle‐aged men

The current RDA for protein for older individuals is 0.8g/kg/day, however, some research has suggested this requirement may be higher. Our aim was to assess the acute effects of feeding and resistance exercise on leucine oxidation with graded quantities of ingested beef. Design 36 healthy older men (58.9 ± 5.2 yr, 1.75 ± 0.1 m, 82.6 ± 12.7 kg) reported to the laboratory in the post‐absorptive state. Catheters were inserted in an antecubital vein to infuse stable isotope labeled leucine ‐ [1‐ 13 C]. Subjects performed an intense bout of unilateral knee extension resistance exercise. After exercise, participants were randomly assigned to one of four feeding conditions, which included 0, 57, 113, or 170 g of beef. Protein synthesis and whole body leucine oxidation were measured over 4 h after exercise by collection of expired labeled CO 2 and plasma α‐ketoisocaproic acid and the reciprocal pool model. Results Leucine oxidation was significantly increased when 170 g of beef was ingested. This amount of dietary protein is in excess of what may be incorporated into tissue protein, which results in irreversible oxidation.