Why are carbohydrates called the "first energy source of the body", but not "main energy source of the body"?

The energetics of biology dictate that carbohydrates are the "first" choice for a cell when given the choice between Carbohydrates, Fats, and Proteins to decompose and produce ATP for the cell to use. There are three main mechanisms to get a carbohydrate to a usable state: glycolysis, citric acid cycle, and the electron transport chain. Furthermore, the carbohydrates represent easier chemical formulations to decompose than say fats, which are made up of much more Carbon, Hydrogen, and Oxygen molecules.

Carbohydrates are called the "first energy source of the body" because they are readily available for immediate energy production. However, they are not the "main energy source of the body" because the body can also use fats and proteins for energy, especially during periods of low carbohydrate intake or prolonged physical activity.