Circadian rhythm. In many people their liver releases a bunch of glucose right before waking, something diabetics term the "dawn effect" and need to control for. This helps get the metabolism going first thing in the morning (at least, in non-diabetics) and delays the need for caloric intake until later in the day. This effect is easily witnessed if you check your blood glucose before bed and when you rise in the morning: for example earlier in the week mine was around 5.4 mmol/L (normal) at bed time and 8.6 mmol/L (high for fasting blood glucose) before breakfast the next day.

A normal person will need caloric replenishment during the day, especially later in the day before (typically) an 8 to 10 hour fast during the night.

So, small proteine-heavy breakfast, large balanced dinner in the evening with a smaller balanced mid-day meal in the middle.