"我长胖了" 英文可以表达为 "I have gained weight." 或 "I have put on weight."

这个短语的来源可能是源自于肉体上体重的增加，通常是指体重增加了一些磅或公斤。

下面是一些例句：

"I can't fit into my jeans anymore. I think I have gained weight." (我的牛仔裤穿不进去了。我想我长胖了。)
"I have put on a few pounds since I stopped going to the gym." (我停止去健身房后体重增加了几磅。)
"I'm trying to watch what I eat because I don't want to gain any more weight." (我在尽量注意自己吃的东西，因为我不想再长胖了。)