Leucine kinetics in reference to the effect of the feeding mode as three discrete meals

In a recent study, we observed that the 24-hour leucine oxidation measured when three equal meals providing a generous intake of leucine (similar to 9 0 mg . kg(-1) . d(-1)) are eaten during the day is 16% lower (P < .01) than that for the same diet given as 10 hourly, equal meals. We hypothesized th at the pattern of meal intake at a lower level of dietary leucine would aff ect the 24-hour rate of leucine oxidation and possibly improve the retentio n of dietary leucine. A total of 11 healthy adults participated in this inv estigation. The daily leucine intake was 182 mu mol . kg(-1) d(-1) (38 mg . kg(-1) d(-1)) given with an L-amino acid diet. All subjects received three discrete meals daily for 6 days prior to a 24-hour intravenous (IV) tracer infusion of L-[1-C-13]-leucine on day 7 (study 1). Four of these subjects participated in two additional studies of similar design, Study 2 involved giving [l-C-13]-leucine as a constant IV infusion together with tracer adde d to the amino acid mixture at each meal time. In study subjects received t he three meals with added [1-C-13]-leucine tracer while [H-2(3)]-leucine wa s given as a constant IV infusion. Total leucine oxidation in studies 1 and 2 was 238 +/- 66 and 231 +/- 85 mu mol . kg(-1) . d(-1), respectively. Leu cine balance was positive, amounting to 18% of the total (diet + tracer) in take. The estimated mean nitrogen balance was +8 mg . kg(-1) d(-1). Leucine oxidation was higher (P < .01) for breakfast than for the lunch meal. This difference was associated with lower insulin and higher plasma leucine con centrations at breakfast: versus lunch periods. The results from study 3 su ggest that the higher rate of leucine oxidation observed at breakfast as co mpared with lunch is not due to a difference in the immediate splanchnic fa te of absorbed leucine from each meal. In comparison to our previous small frequent-meal studies, the pattern of meal feeding influences overall leuci ne utilization at both generous and limiting leucine intakes. Hence, it is possible that the pattern of meal feeding may affect estimations of amino a cid requirements using the tracer-balance approach. Longer-term dietary stu dies will be needed to establish whether and the extent to which this is so . Copyright (C) 1999 by W.B. Saunders Company.