Which tense can I use?

Question

Which is correct:

"I think you should go on a diet.You are putting on weight."

or

"I think you should go on a diet. You have put on weight."

Answer 1

Both of your sentences are correct and understandable, both mean the person has gained weight in the past.

"Putting" implies the person at this moment is still gaining weight, "have put" means the person has already gained whatever weight they were going to gain.