You've actually got that backwards... carbs are quick and easy to digest.
If you have a meal with a lot of simple carbs, however, without much fat/protein/fiber, then the sugars will get into your bloodstream very quickly (can cause a "sugar high"), and then when the sugar is gone, you will "crash." Basically, your body got momentarily used to having a lot of sugar, and when it ran out (because it's digested so quickly), the body needs time to adjust again.
If you have more complex carbs instead of simple carbs, and fiber mixed with some protein and fat, this doesn't happen, because the other stuff - especially the fat - slows down the absorption.
Sugar is more easily digested and more easily used for energy than fat. That's exactly why if you eat a lot of fat and sugar, the body burns the sugar... and, not needing the fat for fuel, just stores it away in your fat cells. It's easier than burning it.
The only way to stop the body from preferring sugar over fat is to give it something even easier to burn for energy, like alcohol.