You just need to ask your friends up front for whatever would be most helpful. If that means saying something like: it would help me the most if you refrain from commenting in what or how much I am eating. I promise I will do my best, even though it may not look like it to you. - that would be okay. On the other hand, if you want your friends to help hold you accountable, its okay to ask for that too. Just ensure you don't make them responsible, what you eat or don't eat is up to you.
I hope you have a really wonderful vacation!!