No matter how much sugar and starch you take into your body, it will either get used or stored. Every gram of sugar that enters your body begins to digest as soon as it hits the saliva. Saliva has an enzyme that breaks down starches and complex sugars. As the sugar and starch breaks down it is absobed through the eiptheilial tissues: gums, cheaks, esophgeal lining, stomach. If a sugar or starch makes it past the acid bath in your stomach it can even be absorbed through the small intestine. Starches and sugars break down into Glucose.
As sugar is taken into the bloodstream a proportionate amount of insulin is released into the bloodstream to deal with the increased sugar levels. The insulin is responsible to allowing cells to uptake the glucose into the cells. The glucose in the cells is immedietly used by the cells. Some of the energy from the glucose is used to aid in the storage of fat that was taken in with the sugar.
Any excess blood-glucose is filtered out into the liver where the excess sugar is turned into FAT (triglycerides).
So, to answer your question, the excess amounts of sugar that you intake, not only making you hyper, increase the insuling levels in your blood to an elevated state. The consquence of excess sugars in your blood lead to you liver catabolizing the sugars into trigylcerides. The extra insulin that is left in the blood will in turn create a 'sugar craving' that will tell your body that you are hungry even though you could be full.
Now, fat is not necessarily a bad thing, fat lines the axons of you nerve cells and makes up a majority of the linings of your cells. Without certain levels of fat in your blood you could risk the production of cells with irregular cell walls, compromising the lifespan of said cells. If you have ever seen anyone who was 'OCD' about fat and would not intake a half a gram a day, over a long period of time they do tend to have decreased health and may develop a sensitivity to fat, which in turn, could lead to diminished galbladder function.
All in all, it is unhealty to live off of any 'restrictive diet', if said restriction is a TOTAL restriction. Sodium restrictive diets can lead to electrolyte imbalance, and such.
Be smart, eat more protein, eat beneficial lipids (nut oils, olive oils, fish oils, Omega-3) avoid trans-fats like the devil! Drink plenty of water, and attempt to limit glycemic-(simple) sugars as much as possible. Simples sugars actually create a fenzy of metabolic activity that would take me many more pages to explain.
-SF