Pinkie Pie is actually a pegasus.
Pinkie's wings move so fast that they can't be seen. (Like a hummingbird's, only faster.)
Pinkie's wings are moving at this super speed at all times, even when she's sleeping, thus requiring her vast intake of calories, namely sugar and sweets.
In fact, Pinkie's wings move so quickly, that they're slightly out of phase with the rest of reality, which is why they never hit anything.
Pinkie's Pinkie Sense is a result of a slight awareness of the momentary future in which her wings exist.

I believe that this theory can explain all of Pinkie's odd powers and abilities.
Feel free to leave comments below.