As discussed previously, glucose is stored in the body as glycogen. While glycogen provides a ready source of energy, lipids primarily function as an energy reserve. As you may recall, glycogen is quite bulky with heavy water content, thus the body cannot store too much for long. Alternatively, fats are packed together tightly without water and store far greater amounts of energy in a reduced space
Now I understand when decide to cutting, the fast fat (carbs) energy goes first and you have a small sensation of losing a little weight, but then after this period of fast energy burn, to burn the calories and really lose some fat "the compacted and dense fat" is harder, takes more time