People can and will sabotage you. Some do it out of jealousy, some do it out of ignorance and some don't even know they're doing it. The most common thing I hear is, "Oh! You're still doing that diet?" Most people seem to assume that you'll fail or that it's a fad you're going through.

To me, it seems that some people don't like when others are successful at something they've failed at, so they immediately try to bring the other person down.

"So-and-so did that diet and gained all the weight back!"

"I heard that diet was dangerous and could kill you!"

"There's no way you can eat like that for the rest of your life!"

"You've lost too much weight already! That must be unhealthy."

"Here, try this. Just one won't hurt you!"