My roommate keeps on snacking. she's eating lots of vegetables but gives up eating rice. how can i help her to practise a healthy diet? she's 19.

Here's an idea: I'm glad you care. Nobody likes to be told what to do, especially when you're almost grown up. Actually, i'm glad she's doing vegetables -- many folks don't. Rice isn't essential and neither is the traditional 3 meals per day. If she's becoming obese she probably would like a good model. The best you can do is invite her to eat out with you and offer her / suggest healthy stuff.