Verb to do

I do look fat.

The sentence is correct. Do makes the sentence more emphatic. Do is the present tense verb and look is an infinitive. Grammatically, look is the same infinitive as in these sentences:

I don't look old.
Do they look good?
He doesn't look young.

CB

Swizzkickz Can you have more than one verb to do in a sentence?e.g "i do look fat"

Yes. The verb "do" is an exception.
Bob flies kites.
Does he do it well?
Yes, indeed. He does do it well. He won the top prize in the kit-flying contest.
Do you do it too?

Swizzkickz can you have more than one verb to do in a sentence?e.g "i do look fat"

That's an odd question because I do look fat has only one 'do'. ???

You can have one emphatic auxiliary 'do', as in your sentence (do look), or you can have a sentence with both auxiliary 'do' and main verb 'do' (I do not do that.).