“长肥”常见的英文表达可以是 “gain weight” 或 “put on weight”，这两个短语都表示体重增加、变胖的意思。例如：
I've been eating too much lately and I've started to gain weight.（我最近吃得太多了，开始长肥了。）
She's worried about putting on weight after the holiday.（她担心假期后会变胖。）