But, it seems to me that it is not. Isn't it obvious that you will not lose weight unless you eat calories than what you burn? If not, why not?

I ask this in a specific context. I have been lurking at HN for over a year and I love how people can get straightforward advice on new business ideas. So I want to get your opinion on my idea.

I want to start a service for people who want to lose weight. But I want to use technology (Twitter/Facebook/SMS) to help them. I want their friends to help them lose weight by pestering them when they are at a restaurant eating a big portion. Sort of like a "social weight loss" program.

What do you think of the idea? Ask me questions but also try to answer my question above. Thanks.

EDIT: tl;dr: Would it be useful if just before you eat, you SMS out what you are about to eat and get an estimated calory count back instantly via SMS?