增肥在英语中可以用 "put on weight" 来表达。这个说法的来源可能是因为人们会在身上增加体重，就像把重物放在物体上一样。例如：

I've been trying to put on weight for the past few months, but it's been difficult.

After the birth of her child, she put on a lot of weight and struggled to lose it.

My doctor told me I need to put on weight to be healthy.

中文翻译如下：

我过去几个月一直在努力增肥，但是很难。

她的孩子出生后，体重增加了很多，很难减肥。

我的医生告诉我我需要增肥来保持健康。