"When we eat our meals, ideally we should eat like a King in the morning, a Prince at noon, and a pauper at night.  We eat such BIG meals at night because we are so hungry from not eating right all day and then we have a big dessert afterwards then go to bed!!  Hard to digest all that.

So ideally we should eat our biggest meal in the morning since we haven't eaten all night.  We are 'breaking our fast' in the morning therefore it is called breakfast."