How much protien can a person eat each day without it becoming toxic?

I have been looking at lowering the carbohydrates in my diet and replacing them with proteins, but there seems to be much disagreement as to what is a toxic amount, some websites even claim that having a carb free diet is harmless, whereas others claim eating only certain protein (such as that found in soy) has no toxicity level. As you can imagine this has left me without any idea if it is in fact safe to do so. Maybe somebody out there has actually used a high protein diet, if so what problems, if any, did it cause?