Fernstrom J D
University of Pittsburgh School of Medicine, PA 15213.
J Am Diet Assoc. 1994 Jan;94(1):71-7. doi: 10.1016/0002-8223(94)92045-1.
Two groups of amino acids--the aromatic and the acidic amino acids--are reputed to influence brain function when their ingestion in food changes the levels of these amino acids in the brain. The aromatic amino acids (tryptophan, tyrosine, phenylalanine) are the biosynthetic precursors for the neurotransmitters serotonin, dopamine, and norepinephrine. Single meals, depending on their protein content, can rapidly influence uptake of aromatic amino acid into the brain and, as a result, directly modify their conversion to neurotransmitters. Such alterations in the production of transmitters can directly modify their release from neurons and, thus, influence brain function. The acidic amino acids glutamate and aspartate are themselves brain neurotransmitters. However, they do not have ready access to the brain from the circulation or the diet. As a result, the ingestion of proteins, which are naturally rich in aspartate and glutamate, has no effect on the level of acidic amino acid in the brain (or, thus, on brain function by this mechanism). Nevertheless, the food additives monosodium glutamate and aspartame (which contains aspartate) have been reputed to raise the level of acidic amino acid in the brain (when ingested in enormous amounts), to modify brain function, and even to cause neuronal damage. Despite such claims, a substantial body of published evidence clearly indicates that the brain is not affected by ingestion of aspartame and is affected by glutamate only when the amino acid is administered alone in extremely large doses. Therefore, when consumed in the diet neither compound presents a risk to normal brain function.
两类氨基酸——芳香族氨基酸和酸性氨基酸——据说当它们在食物中的摄入量改变大脑中这些氨基酸的水平时，会影响大脑功能。芳香族氨基酸（色氨酸、酪氨酸、苯丙氨酸）是神经递质血清素、多巴胺和去甲肾上腺素的生物合成前体。单餐饮食，取决于其蛋白质含量，可迅速影响芳香族氨基酸进入大脑的摄取，结果直接改变它们向神经递质的转化。神经递质产生的这种改变可直接改变它们从神经元的释放，从而影响大脑功能。酸性氨基酸谷氨酸和天冬氨酸本身就是大脑神经递质。然而，它们无法从循环系统或饮食中轻易进入大脑。因此，摄入天然富含天冬氨酸和谷氨酸的蛋白质，对大脑中酸性氨基酸的水平（或通过这种机制对大脑功能）没有影响。尽管如此，食品添加剂味精和阿斯巴甜（含有天冬氨酸）据说（大量摄入时）会提高大脑中酸性氨基酸的水平，改变大脑功能，甚至导致神经元损伤。尽管有这些说法，但大量已发表的证据清楚地表明，大脑不受阿斯巴甜摄入的影响，只有当单独以极大量给予氨基酸时，大脑才会受谷氨酸的影响。因此，当在饮食中食用时，这两种化合物都不会对正常大脑功能构成风险。
