This kind of tea could act as an aid to digestion.

这种茶可以助消化。

act as:

1) do the work of; serve as 当作；充当

2) play the role of 担任……的角色

　　再如：
　　A trained dog can act as a guide to a blind person.
　　一条经过训练的狗可以给盲人当向导。

　　One of his friends acted as the gobetween in this business.
　　在这件事中，他的一个朋友充当了中间人。