Kim S H, Mauron J, Gleason R, Wurtman R
Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, 0239.
Int J Vitam Nutr Res. 1991;61(2):166-79.
In order to determine the spontaneous macronutrient choice of a normal rat population, we allowed growing animals to choose their food among three isocaloric diets: 5% protein - 40% carbohydrate; 45% protein - 40% carbohydrate and 5% protein - 70% carbohydrate, and we measured macronutrient intake, carbohydrate to protein (C/P) ratio and weight gain twice weekly during 9 weeks. At the end of the study, final body weight gain and fat accretion as well as brain serotonin content were measured. Protein consumption increased and fat intake decreased steadily during the assay (from 18.8 to 29 kcal% vs. 35.7 to 25.2 kcal%) whereas carbohydrate consumption remained constant (approx. 46 kcal%) ("carbohydrate homeostasis"), and as a consequence the C/P ratio dropped. There were great variations in total protein consumption between animals (13-32 kcal%) and an inverse relationship with fat intake because carbohydrate consumption was constant. Daily weight gain was negatively correlated with the corresponding C/P ratio, as were final weight gain and body fat content with the global C/P ratio characterizing the food choice of each rat. The concentrations of brain serotonin and 5-hydroxyindole acetic acid were rather uniform and did not show any correlations with any of the other variables. The percent food protein chosen by the animal determined the outcome of the trial at 9 weeks, i.e. food intake, weight gain and body fat accretion. In this experimental model, body fat accumulation is, therefore, directly linked to the protein content of the diet, inversely proportional to the fat level and not related to the carbohydrate content. Since the animals increase the proportion of protein in their food with age above basic nutritional requirements, it is postulated that the macronutrient choice of the rat is also determined by the need of the brain for a proper and balanced supply of neurotransmitter precursors adapted to the situation of each animal.
为了确定正常大鼠群体对常量营养素的自发选择，我们让生长中的动物在三种等热量饮食中选择食物：5%蛋白质 - 40%碳水化合物；45%蛋白质 - 40%碳水化合物和5%蛋白质 - 70%碳水化合物，并在9周内每周两次测量常量营养素摄入量、碳水化合物与蛋白质（C/P）比值和体重增加。在研究结束时，测量最终体重增加、脂肪堆积以及脑血清素含量。在实验过程中，蛋白质消耗量增加而脂肪摄入量稳步下降（从18.8至29千卡% 对比 35.7至25.2千卡%），而碳水化合物消耗量保持恒定（约46千卡%）（“碳水化合物稳态”），结果C/P比值下降。动物之间的总蛋白质消耗量存在很大差异（13 - 32千卡%），并且与脂肪摄入量呈负相关，因为碳水化合物消耗量是恒定的。每日体重增加与相应的C/P比值呈负相关，最终体重增加和体脂含量与表征每只大鼠食物选择的总体C/P比值也呈负相关。脑血清素和5 - 羟吲哚乙酸的浓度相当均匀，并且与任何其他变量均无相关性。动物选择的食物蛋白质百分比决定了9周试验的结果，即食物摄入量、体重增加和体脂堆积。因此，在这个实验模型中，体脂积累与饮食中的蛋白质含量直接相关，与脂肪水平成反比，与碳水化合物含量无关。由于动物随着年龄增长，在基本营养需求之上增加食物中蛋白质的比例，因此推测大鼠对常量营养素的选择也由大脑对适应每只动物情况的神经递质前体进行适当和平衡供应需求所决定。
