questions concerning calories metabolism and protein

I'll take the protein question for you. Protein is composed of subunits called amino acids. If you've heard of enzymes -- which our cells use to survive -- these are a type of protein that our cells make. These and other proteins made and used by our cells are built from amino acids in the proteins we eat. Muscle tissue, for example, is packed with several large proteins (with names like actin, myosin, dystrophin, and tropomosin just to name four). Our red blood cells contain a large protein you may have heard of called hemoglobin which is used to carry oxygen around our bodies. A large amount of our dietary protein is NOT used for energy but rather is used by cells to build other proteins that we need.

When protein is used as an energy source by our cells, an amino group (this is a term from biochemistry) has to be removed from each amino acid being broken down for energy. This produces toxic waste in the form of substances like ammonia (highly nasty stuff which can be converted to less toxic urea which is released from the body in sweat (to a lesser degree) and urine (to a greater degree).

Bottom line is that it is hard to over-consume protein, even if you are relatively sedentary in your lifestyle. Full blown protein should really never end up in the urine (for reasons that are too complicated for this post...really the two worst things to see in large amounts in your urine are protein and blood cells because this indicates a serious kidney malfunction...) but when protein is used as an energy source extra nitrogenous waste (i.e. urea) ends up in your urine. Since dietary protein is so important for building other proteins in our cells, there is minimal chance of excess protein being converted to fat. (Carbs are a different story, but only when consumed to excess...and carbohydrates in the form of the simplest sugars start and fuel basic cellular metabolism, so cutting too much carbohydrates out of your diet prevents cells from effectively breaking down fats and forces the burning of proteins for fuel. Fats are used to store energy, as a source of energy, and like proteins are used by cells to build a host of important structures, including our cellular membranes and various signal molecules.)

This is probably a longer and more technical answer than you were looking for, but I teach anatomy, physiology, and cell biology to nursing and other students so I think it's important to be as accurate as possible in covering this.

Simple summary answer now: Hard to eat too much protein; protein is not going to be converted to fat or end up directly in the urine but when used excessively for energy contributes to production of toxic substances in our cells which end up in the urine. Real bottom line: of proteins, carbs, and fats, don't cut too much of any one out of your diet; your cells need all three!