Eating habits

Most news stories and articles that are out these days talk about childhood obesity being at an all time high. In our home, with Isabelle, it's more like childhood starvation! My daughter Isabelle won't eat! Over the past 3 days she has not sat down to eat a meal at the table. She has to be hungry, I rarely let her have a snack. It's not as if we are offering foods that she would not like. She has turned down pizza, grapes, grilled cheese, spaghetti Os and more. She will drink things so I am satisfied for now knowing that she is getting milk, water and juice throughout the day. She doesn't claim to feel sick, she just doesn't want to eat. Today, I know she hates taking a nap so I told her it was eat or sleep and she chose to sleep. Does anyone think I should be worried? She is little,always has been, only weighing about 25lbs and she is almost 3, but she is also very active. In my logical thinking-I think if she is running around, she must be hungry burning the calories. I don't want to force the issue and come down on her for it, but I make it very clear that the meal is only offered once and there are no snacks or treats if she doesn't eat a good meal. How have you handled these situations or what would you try?