Postprandial oxidative losses of dietary leucine depend on the time interval between consecutive meals: A model study with rats

Postprandial oxidative losses of egg white-bound [1-¹³C]-leucine were studied as ¹³C recovery in the breath of rats in relation to different time intervals between two meals. Male Wistar rats (n = 48; 68.3 ±5.9 g) divided into 4 groups (n = 12) were fed two meals a day (9:00 and 16:30; interval 7 h) of a 13.2% egg white-based diet for 30 min. After 14 days, 3 out of the 4 groups received the 2^nd meal at shorter time intervals of 3, 1, and 0 h. Two [¹³CO₂] breath tests (BT) were performed on days 19 and 40. The breath samples were analyzed for ¹³C Atom % (At %) enrichment by IRMS, and the results were expressed as the rate of ¹³C At % excess and cumulative recovery (% of dose). The 7 h interval group showed higher ¹³C cumulative recovery after the 2^nd meal during both the BT and after the 1^st meal on the day 40 BT compared with the 3, 1, and 0 h intervals. In groups with the 3, 1, and 0 h intervals, the cumulative recovery of ¹³C after the 2^nd meal was lower compared with the 1^st meal due to interaction between meals, which probably caused dilution of the tracer in the larger volume of feed in the rat's stomach. On day 40, all cumulative recovery values were higher than on day 19. An important finding of this study is that despite the differences in postprandial Leu oxidation among interval groups, the weight gain of all rats was similar.