Eat a lot of vegetables and fruit
The problem is that your body wants to have it easy, like he is used to. It's easy to get energy from carbs and sugar, but if your eating lean chicken breast and vegetables for examples (my favourite lunch :) )your body has to work. But he doesn't want to. So he is annoying you until your eating something from which it's easy to get energy from.
Don't let your body win. He gets what he need, he's just like a naughty child :P
(I hope I've translated everything right I'm not really sure about the carbs maybe someone with a better english can correct me if that's not right )
But I think you still got the overall message.