I am very much a fan of Ajahn Brahm when it comes to this. In all of his talks that listened to (and there were many) he never mentioned "honesty" (in the sense of speaking factual correctness). He always talks about skillful speech. Also, he stresses that to him, the definition of truth is that which brings peace and harmony. If something leads to argument, to disagreement, to division, how can it be true? Following this argument, saying "you don't look fat in that at all" can be 'true'/skilfull even when it isn't a factual truth.
To me, I tend to focus on what the speech causes. If someone was nervous about doing something and then asks "did I do ok?" when they didn't, I may well say "yes" because this conveys that I have confidence in them, which is the truth, whereas saying "no" would convey that I did not have confidence in them, which would be false. However, this is a slippery slope and the way I see it, it needs to be balanced with humble, honest personal reflection to ensure the intention wasn't to deceive, just as the others have mentioned.
But the best advice is to just always eat pasta with sauce, you avoid the problem and it's much healthier and less gross as well!