Remember that we're discussing a case where the person asked you for your opinion.

The quoted hypothetical doesn't make clear if the information is asked for or volunteered. Nor does it make clear what it would mean to tell the truth: "Yes, that dress makes you look fat."; "That dress makes you look fat because you look fat in any dress because you're fat"; "You look fat in any dress and that's why men are not interested in you"; or something else.

Do you really think this is the case for good friends, or loved ones?

Probably not . . . but I don't think it affects my point, which is that a lot of the time, people express concern, and might even believe that they are acting out of concern, but actually they have other motivations.

And furthermore, do you in fact believe that not having the money for a gym membership is the important obstacle between an overweight person and an effective weight-less solution?

No I don't. But I'm skeptical that the lack of an additional reminder is an obstacle either.