“你很瘦”用英语可以说："You are very thin."

这句话的来源是源自英语中描述人体健康状况的常用词汇。在英语中，“瘦”通常用 thin 来表示。

例句：

"She is very thin. She needs to eat more to gain weight." （她很瘦，她需要多吃点东西来增重。）

"He used to be thin, but now he has gained some weight and looks healthier." （他以前很瘦，但现在体重增加了一些，看起来更健康。）

"Being thin doesn't always mean that someone is unhealthy. Some people naturally have a thin body type." （瘦并不一定意味着有人不健康。有些人天生体型瘦。）