建议使用官方纸质指南，查看对照完整题目
It was once believed that the brain was independent of metabolic processes occurring elsewhere in the body. In recent studies, however, we have discovered that the production and release in brain neurons of the neurotransmitter serotonin (neurotransmitters are compounds that neurons use to transmit signals to other cells) depend directly on the food that the body processes.
Our first studies sought to determine whether the increase in serotonin observed in rats given a large injection of the amino acid tryptophan might also occur after rats ate meals that change tryptophan levels in the blood. We found that, immediately after the rats began to eat, parallel elevations occurred in blood tryptophan, brain tryptophan, and brain serotonin levels. These findings suggested that the production and release of serotonin in brain neurons were normally coupled with blood-tryptophan increases. In later studies we found that injecting insulin into a rat’s bloodstream also caused parallel elevations in blood and brain tryptophan levels and in serotonin levels. We then decided to see whether the secretion of the animal’s own insulin similarly affected serotonin production. We gave the rats a carbohydrate-containing meal that we knew would elicit insulin secretion. As we had hypothesized, the blood tryptophan level and the concentrations of tryptophan and of serotonin in the brain increased after the meal.
Surprisingly, however, when we added a large amount of protein to the meal, brain tryptophan and serotonin levels fell.Since protein contains tryptophan, why should it depress brain tryptophan levels? The answer lies in the mechanism that provides blood tryptophan to the brain cells. This same mechanism also provides the brain cells with other amino acids found in protein, such as tyrosine and leucine. The consumption of protein increases blood concentration of the other amino acids much more, proportionately, than it does that of tryptophan. The more protein is in a meal, the lower is the ratio of the resulting blood-tryptophan concentration to the concentration of competing amino acids, and the more slowly is tryptophan provided to the brain. Thus the more protein in a meal, the less serotonin subsequently produced and released.
It can be inferred from the passage that which of the following would be LEAST likely to be a potential source of aid to a patient who was not adequately producing and releasing serotonin?
我有更好的解析 
暂无雷哥网文字解析
从题干可知，必须选择一个“降低”其S物质水平的选项，如此对其的帮助才最小。根据文章最后一句可知，摄入的蛋白质越多，随之产生和释放的S物质就越少
A正确，“几乎只含有蛋白质的食物”会迅速降低S物质的水平
B错误，含糖的食物会提高S物质的水平
C错误，胰岛素也会提高S物质的水平
D错误，其他氨基酸浓度越小表明蛋白质越少，S物质的水平就越高
E错误，理由同上
为什么定位在最后一句？第二段也讲了很多producing和releasing
0
0
回复
2019-09-25 20:14:08
并列 "sero ↓；potential aid ？ →意在sero ↑ → LEAST 与 sero负相关 "
0
0
回复
2019-07-24 16:25:52
文章最后一句：Thus the more protein in a meal, the less serotonin subsequently produced and released.
0
0
回复
2018-06-16 17:26:10
Meals consisting almost exclusively of protein 饭菜几乎完全由蛋白质组成 exclusively - 必应词典 美[ɪkˈsklusɪvli]英[ɪkˈskluːsɪvli] adv.仅仅；专门地；特定地；排外地 网络专有地；唯一地；独占地
0
0
回复
2016-04-04 20:27:06
科目：
阅读RC
来源：
OG16
1m55s
平均耗时
71.8%
平均正确率
该题由网友5WOcOWKo提供 上传GMAT题
分享
周末、晚班滚动开班 
24+35+35+6课时 
