put on weight意思是发胖。
同义词：
gain weight增重/变胖
get fat长胖
fill out长胖
flesh up长胖
例句：
That's terrible for your health. It's easy to gain weight that way.
那对你的健康很不好。那样很容易长胖。
Chocolate does contain large quantities of energy, so if you eat too much of it, you can put on weight.
巧克力确实含有高度热量，所以如果你吃太多，你的体重会增加。