"发胖"用英语可以表示为"gain weight"或"put on weight"。
"Gain weight"是"增加体重"的
意思，来自动词"gain"，
意思是"获得，增加"，加上名词"weight"，
意思是"体重"，所以"gain weight"就是"增加体重"的
意思。
"Put on weight"也是"增加体重"的
意思，来自动词"put on"，
意思是"穿上，戴上"，加上名词"weight"，
意思是"体重"，所以"put on weight"就是"增加体重"的
意思。
下面是一些使用"gain weight"和"put on weight"的英文例句及其中文
翻译：
I've been eating too much junk food lately and have gained a lot of weight. (最近我吃了太多垃圾食品，体重增加了很多。)
I'm trying to put on weight because I'm too thin. (我在努力增加体重，因为我太瘦了。)
After having a baby, I put on a lot of weight that I couldn't lose. (生完宝宝后，我体重增加了很多，我没法减掉。)
I've been working out and eating healthy, but I still can't seem to gain weight. (我一直在锻炼身体，吃健康食品，但是我仍然不能增加体重。)
