题目内容：

A Diet Without Enough Protein Can Cause Depression

Depression is a condition so common. 1. The World Health Organization (WHO) calls it “a leading cause of disability.” Difficulty in falling asleep, loss of appetite, and loss of ability to concentrate are just a few of the other effects of depression. While life events such as the loss of a spouse or a job may create a happening of depression, many cases come from within, such as people’s diet.

As is reported, both before and during a happening of depression, those with the condition show a “poor appetite”. 2. On the other hand, depression may be closely related to protein. Many cases of depression happen to those who don’t eat properly, which then result in lack of protein taken into the body.

3. It all comes down to amino acids (氨基酸). Proteins are made up of amino acids. Both the human brain and nervous system use amino acids as a substance that creates a signal from one brain cell to another or one nerve cell to another. With them communication between the cells becomes possible.

4. But eight of them, the “essential” ones for communication between the brain cells, must be eaten in one’s diet. So a diet which is lacking in protein lessens the signal being sent from one brain cell to the next during a thought. The process can lead to twisted signals, which can not only lead to depression, but also aggression. 5.

A. It happens with aggression.

B. It may lead to serious effects.

C. But how lack of protein occurs?

D. There are 20 different amino acids.

E. But what does protein have to do with depression?

F. The poor appetite itself can create a depressed mood.

G. This is why depression can often express itself as anger or aggression.