Jackson A A, Doherty J, de Benoist M H, Hibbert J, Persaud C
Department of Human Nutrition, University of Southampton.
Br J Nutr. 1990 Sep;64(2):371-85. doi: 10.1079/bjn19900039.
The kinetics of urea metabolism were measured in children recovering from severe malnutrition. For a period of up to 10 d they received one of four diets which provided 711 kJ (170 kcal)/kg per d. Two groups received a diet with a high protein:energy (P:E) ratio of 10-6% (HP), enriched with either fat (HP/F) or maize starch and sucrose (HP/C). Two groups received a diet with a low P:E ratio of 8.8% (LP), enriched with either fat (LP/F) or maize starch and sucrose (LP/C). The rate of weight gain on the HP diets was significantly greater than on the LP diets. There was no difference in urea production between any of the four diets: HP/F 1.23 (SE 0.12), HP/C 1.37 (SE 0.14), LP/F 1.64 (SE 0.22), LP/C 1.15 (SE 0.15) mmol nitrogen/kg per h. On the HP diets urea excretion was 0.77 (SE 0.07) mmol N/kg per h, 61% of production. There was significantly less urea excreted in the urine on diet LP/C than on LP/F (0.36 (SE 0.05) and 0.64 (SE 0.04) mmol N/kg per h respectively). A significantly greater percentage of the urea production was hydrolysed on the LP diets (61%) compared with the HP diets (39%), with the consequence that 50% of urea-N produced was available for synthetic activity on the LP diets compared with 30% on the HP diets. The increase in the urea hydrolysed on the LP diets was equivalent in magnitude to the decreased intake of N, so that overall intake plus hydrolysis did not differ between the LP and the HP diets. Crude N balance was similar on diets HP/F, HP/C and LP/C, but was significantly reduced on diet LP/F. These results show that there is an accommodation in urea kinetics during rapid catch-up weight gain, which becomes evident when the P:E ratio of the diet falls to 8.8%. It is proposed that, for a P:E ratio of 8.8%, protein is limiting for catch-up growth. When the intake has a P:E ratio of 8.8% the pattern of urea kinetics can be modified by the relative proportions of fat and carbohydrate in the diet. The measurement of urea kinetics provides a useful approach to the definition of the adequacy of the protein in the diet.
对严重营养不良恢复期儿童的尿素代谢动力学进行了测定。在长达10天的时间里，他们接受了四种饮食中的一种，这些饮食每天每千克提供711千焦（170千卡）的能量。两组接受高蛋白能量（P:E）比为10 - 6%的饮食（HP），分别富含脂肪（HP/F）或玉米淀粉和蔗糖（HP/C）。另外两组接受低P:E比为8.8%的饮食（LP），同样分别富含脂肪（LP/F）或玉米淀粉和蔗糖（LP/C）。HP饮食组的体重增加速率显著高于LP饮食组。四种饮食之间的尿素生成量没有差异：HP/F组为1.23（标准误0.12）、HP/C组为1.37（标准误0.14）、LP/F组为1.64（标准误0.22）、LP/C组为1.15（标准误0.15）毫摩尔氮/千克每小时。在HP饮食组中，尿素排泄量为0.77（标准误0.07）毫摩尔氮/千克每小时，占生成量的61%。LP/C饮食组尿液中排泄的尿素显著少于LP/F饮食组（分别为0.36（标准误0.05）和0.64（标准误0.04）毫摩尔氮/千克每小时）。与HP饮食组（39%）相比，LP饮食组中尿素生成被水解的比例显著更高（61%），结果是LP饮食组中50%的尿素氮可用于合成活动，而HP饮食组为30%。LP饮食组中水解的尿素增加量在幅度上与氮摄入量的减少量相当，因此LP和HP饮食组的总摄入量加水解量没有差异。HP/F、HP/C和LP/C饮食组的粗氮平衡相似，但LP/F饮食组的粗氮平衡显著降低。这些结果表明，在快速追赶生长期间尿素动力学存在适应性变化，当饮食的P:E比降至8.8%时变得明显。有人提出，对于P:E比为8.8%的情况，蛋白质是追赶生长的限制因素。当摄入量的P:E比为8.8%时，饮食中脂肪和碳水化合物的相对比例可以改变尿素动力学模式。尿素动力学的测定为确定饮食中蛋白质是否充足提供了一种有用的方法。
