There's a lot of misconceptions about starvation mode; it's not about eating a certain number of calories, even. It's not even about a single day of poor choices. It's much more complicated than that.
One day isn't going to hurt you. It's a pattern of poor choices over time that can lead to slowed metabolism. IF it happens, it happens, but you don't want to make a habit of it. It's still important to get the nutrition you need, because you'll feel like crud if you don't.
Here's a thread that will help you understand what starvation mode is (and isn't.) Scroll down to Coach Dean's response. www.sparkpeople.com/myspark/messageboard.a
I keep asking them to make this an expert answer; they don't even have to do much, just add it!