Why are some foods preferentially eaten at certain times of day?
rumtscho's answer is right (upvoted it), it's more custom than anything. In parts of Holland, they eat cheese at breakfast, quite a lot of it. Most Brits these days eat cereal grains of some sort, replacing the old, common breakfast of bacon and eggs. From a nutritional point of view, eating protein in the morning isn't a bad thing to do - it keeps you from feeling hungry for up to four hours, and if you suffer from that sluggish, I can't get going feeling when you get up, eating protein (preferably without carbohydrates such as bread) will help with that. The protein doesn't have to be eggs, can be fish, meat or cheese. Some dieticians argue that we eat the wrong way round - we should have our largest meal in the morning, then a good lunch, with a supper or tea which is significantly smaller than the other meals at the end of the day, on the understanding that you'll be active throughout the day, but not particularly active in the evening.