Why does food never completely fulfill you until you have actually EATEN it?!
Answers:
This can be quite chemical - and not really too mysterious at all.
You learn from doing the Atkins diet that most people eat food which stimulates them to express a LOT of insulin. And insulin makes you hungry later - specifically craving junky foods.
What happens is that you eat foods having lots of highly glycemic stuff - carbs - sugars - starch. This stuff goes to your blood stream and turns to sugar right away - glucose. Then this calls out a LOT of insulin to deal with this. It has to get it out of the blood pretty quickly - so insulin will often over-react. Lots and lots is produced and dumped into your blood. It clears the blood quickly.... and later..... you have LOW BLOOD SUGAR - and you're "Hungry" again - you "need" more sugar - so you really want junk food - sugars - Taco Bell.
Anyway - this is the rollercoaster blood sugar problem you STOP when you do the Atkins diet. The cravings drop off very well - blood pressure, triglycerides, cholesterol drop off - and overall you have less chance of diabetes (unregulated blood sugar).
Think Atkins - it really is remarkable. get a used copy of "New Diet Revolution" off of Amazon Books. There's also a lot of Atkins food-help websites. Lots of doctors do Atkins these days as it's been shown to be quite healthy.