Is it grammatically correct to say "the smartest thing I have done is stop junk food"?

Question

Could you tell me if it's correct and natural to say the following?

The smartest thing I have done is stop eating junk food.

If it's not, thend would it be more natural if I said this way?

The smartest thing I have done is stoping eating junk food.

Answer 1

The correct form is: "The smartest thing I have done is to stop eating junk food".

This is the infinitive form "to stop" used as a noun, also known as a gerund.

As an aside, "stopping" is the correct spelling of that word.