Hi,
No clearly eating too much protein and too much fat will of course result in you putting on weight and/or fat.
Proteins can turn to glucose fairly easily as well.
As I said carbs are the #1 fuel for our bodies. Just by you moving around working, and generally being alive. Digesting/exercising and so on, your body needs to fuel your muscles and your brain and your organs. That's what generally people call minimum calories or RMR, basically what you need to keep your body ticking over.
Your body looks around for carbs stored as glycogen because the conversion process of carbs to energy is very very easy for the body to do (easier than converting fat and proteins to energy). SO there you have it, already, the body doesn't want to use the fat since the carbs are there happy to be used. Our bodies have designed to hold onto fat in case of famine, and lack of knowing when our next meal will present itself to us.... Bloody thing hasn't evolved yet.
Once the body has used the carbs (as you say the 20-30 mins usually), it has converted all the reamining glycogen in your muscles and your liver back into glucose and the body is on empty. Now it is forced to get it's energy from elsewhere so it turns to the fat cells. Hoorah!
Lipolysis (fat breakdown) and beta-oxidation occurs within the mitochondria. It's a cyclical process (citric acid cycle IIRC - don't quote me on that) where two carbons molecules are removed from the fatty acid every cycle into something called acetyl CoA, this oxidisation process carries through the Krebs cycle to produce ATP, CO2 , and water.
This hormonal response induces the fat cells to realease fatty acids and glycerol. These 2 compounds end up in the liver where they are turned into glucose our body's favourite energy source.
As we use up the glucose we start using more fat etc... The cycle continues. Clearly if you don't give your body enough carbs or fats to use it will start breaking down your muscles - however the old wives tale of your body using muscle first is wrong, if you eat well and not reliant on carbs this is what happens.
I can go into a more in depth explanation about metabolism in due course if it interests you - but I might do it in the main thread.
Does that help?